The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadr...The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadruple inclusion and triangular inclusion） under lowvelocity impact loading. By recording the caustic spots of crack tips at different moments during the crack propagation, the variation regulations of dynamic stress intensity factors（ DSIF） and crack growth velocity with respect to time are obtained. The experimental results showthat the resistance effects to crack growth are varied with different shapes of inclusions in specimens, and the quadruple inclusion＇s effect is more apparent. The distortion degree of caustic spots is affected by the shapes of inclusions as well, and the situation is more serious for cylinder and quadruple inclusions. The overall values of DSIFs of triangular inclusion specimen are greater than the others, and the crack growth velocities, characteristic sizes and DSIFs showprocesses of fluctuations because of the disturbance of reflection waves in specimens. The results provide an experimental basis for the analysis of strength and impact-resistance ability in structures with deformity inclusions.展开更多
The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabric...The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.展开更多
Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadwa...Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.展开更多
We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected causti...We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.展开更多
Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are...Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are developed. The dynamic caustics are analyzed for the crack propagating along the interface between two bonded dissimilar materials. The variation of the caustic configurations is shown with the velocity change of the running crack and the ratio change of the stress intensity factors. Two characteristic dimensions are proposed that are not only practically measurable from optical caustic contours but also suitable to represent the behavior of transient caustics.展开更多
The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a...The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a drop hammer system. Caustics information recorded in films illustrated the histories of both crack length and stress intensity factor. The dynamic fracture toughness and crack growth velocity of TA15ELI with lath-like microstructure were determined to be 279 MPa.m1/2 and 32.6 m/s, respectively. SEM fractograph analysis showed a mixed feature of mainly plastic mode for TA 15ELI alloy in dynamic mode-II fracture. Shear localization was observed in the vicinity of the crack initiation area.展开更多
An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using...An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using reflected caustics in combination with the stress freezing and stress releasing technique. The results of this experimental method coincided favorably with the theoretical analysis results of Tweed and Rooke.展开更多
Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation z...Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area.展开更多
In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics ...In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics of drops with an equatorial radius a = 50 μm, 100 μm, 200 μm, and 500 μm are studied at the same drop/beam ratios (i.e. γ the ratio between the droplet equatorial radius and the Gaussian beam waist) using concentric illumination with a Gaussian beam, and the effect of droplet size on the optical caustics is analyzed. The curvature of the rainbow fringe and the evolution of the cusp caustics position, in this case, are obtained;the diameter range of droplet shape (ellipsoid) measured by Gaussian beam illumination is broadened. Based on this model, the effects of the relative positions d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics of the droplet when the center of the Gaussian beam deviates from the droplet center (the center of the Gaussian beam waist is on the same y-axis as the droplet center) are discussed. The optical caustics of the droplet when the center of the Gaussian beam is off the droplet center (the center of the Gaussian beam waist is on the z-axis with the droplet center) are also discussed. The effects of the relative positions of the center of the beam waist and the droplet center d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics are also discussed. A method of measuring droplet shape with Gaussian beam illumination is proposed when the beam waist center is coaxial with the droplet center.展开更多
Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at ...Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at the University Hospital of Brazzaville. Patients and Methods: Prospective study was conducted from January 2014 to December 2015 in the Pediatric Departments of the UHB and centers of digestive endoscopy in Brazzaville. All children who ingested a caustic product and hospitalized were included after obtaining parental’s consent. The studied parameters were: Age, sex, nature and quantity of the caustic, the family’s attitude, clinical signs, endoscopic results according to Zagar’s classification, therapeutic modalities and evolution. Results: 8292 children were hospitalized and 68 because of the ingestion of caustic, a frequency of 0.8%. The average age was 23.6 months [2 months - 16 years]. The male sex was predominant (57.4%). Ingestion was accidental in 88.2% and voluntary in 11.8%. Factors favoring ingestion were storage methods (81.5%) and parental’s inattention or negligence (10.8%). Bleach was the most incriminated caustic (54.4%) followed by caustic soda (29.4%). The estimated quantity ingested was assumed to be minimal in 61.7%. Unsuitable acts were practiced by the family before the medical consultation in 66.1%. The dominant symptoms were digestive (47%) and neurological (25%). The average time to perform endoscopy was 48 hours in 88.2%. Endoscopy revealed lesions in 51.7%, the different stages were I (12 cases), II (16 cases) and III (3 cases). The mains factors of gravity were inappropriate gestures (85%) and the non-respect of the fasting (9%). Proton pump inhibitors were used in 50%. The evolution was favorable for in 73.5%. Conclusion: Ingestion of caustics by children is most often accidental favored by the inadequate packaging and storage. Prevention is about educating people in order to reduce their frequency.展开更多
While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors....While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors.These caustic surfaces,described in a closed form,are also developable surfaces of the same type as the original mirror surface.We provide efficient,algorithmic computation to find the caustic surface of each of the three types of developable surfaces(cone,cylinder,and tangent surface of a spatial curve).We also provide a potential application of the results in contemporary free-form architecture design.展开更多
The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic ...The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic caustic method. The experimental results indicate that the fluctuation of crack propagation velocity v first increases and then decreases in the crack propagation process. During the process of crack propagating into the inclusion area, the fracture resistance effect of the circular inclusion is the most significant and the effects of triangular and square inclusions are less obvious. The stress intensity factor near the crack tip increases during the propagation process and reaches its maximum value when the crack tip is close to the inclusions. The crack tip’s dynamic stress intensity factor （ DSIF） decreases when the crack exceeds the middle area of the double inclusions. These results provide an experimental basis and scientific foundation to strengthen the evaluation and fracture analysis of the structure containing deformity inclusions.展开更多
Caustic ingestion is a relatively rare but potentially catastrophic gastroentero-logical emergency.Upper gastrointestinal(GI)endoscopy is currently regarded as the gold standard modality not only to assess the depth a...Caustic ingestion is a relatively rare but potentially catastrophic gastroentero-logical emergency.Upper gastrointestinal(GI)endoscopy is currently regarded as the gold standard modality not only to assess the depth and the extension of GI caustic injury,but also to guide the appropriate treatment.Intriguingly,contrast-enhanced computed tomography(CECT)has recently emerged as a promising non-invasive and more accurate alternative to endoscopy in this setting.However,to date,evidence concerning the role of CECT as an alternative or complementary diagnostic tool to endoscopy in caustic ingestion is still limited.The aim of our review was to summarize and discuss the current evidence concerning the role of CECT in the emergency diagnosis of caustic ingestion and its value in assessing injury severity among non-pediatric patients.展开更多
Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic ...Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic endoscopy practice, explaining use of traditional as well as new and innovative techniques, for diagnosis and treatment of diseases in the paediatric upper gastrointestinal tract.展开更多
The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carr...The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carried out for two loading rates. By measuring the characteristic dimensions of the shadow spots during the caustic experiments, the dynamic SIFs are calculated for different loading rates. The experimental results indicate that the dynamic fracture toughness Kid increases remarkably with increasing loading rate, and the crack grows faster under the high-velocity impact. Moreover, by examining the crack growth routes and the fracture surfaces, it is shown that the loading rate also greatly affects the failure mechanisms at micro-scale.展开更多
Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photo...Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.展开更多
AIM:To report our experience in the surgical management of severe injuries of the gastrointestinal tract due to corrosive ingestion.METHODS:A retrospective review of patients who underwent emergency surgery for severe...AIM:To report our experience in the surgical management of severe injuries of the gastrointestinal tract due to corrosive ingestion.METHODS:A retrospective review of patients who underwent emergency surgery for severe gastrointestinal injuries following corrosive ingestion between 1983 and 2010 was carried out.Data was extracted from a prospectively maintained esophageal disease database.Severe corrosive injuries were defined as full thickness necrosis with perforation of the esophagus or the stomach(with or without involvement of the adjacent viscera) with resultant mediastinitis or peritonitis.RESULTS:Between 1983 and 2010,209 patients with corrosive injury of the esophagus were managed.Of these,13(6.2%) patients underwent emergency surgery for severe corrosive injury.The median age of the patients was 22 years and the median interval between ingestion of the corrosive substance and surgery was 24 h.The surgical procedures done included esophagogastrectomy alone(n = 6),esophagogastrectomy withduodenectomy(n = 4),esophagogastrectomy with pancreaticoduodenectomy(n = 1),esophagogastrectomy with splenectomy(n = 1) and distal gastrectomy with duodenectomy(n = 1).Two patients died in the postoperative period and one after discharge awaiting the second surgery.The factors significantly predictive of mortality following such an injury included renal failure at the time of initial presentation,presence of metabolic acidosis,delay of more than 24 h between corrosive ingestion and surgery,and corrosive induced adjacent organ injury(pancreatic)(P < 0.001,0.02,0.005 and 0.015 respectively).Ten patients underwent subsequent surgery for restoration of the alimentary tract continuity with a colonic pull-up(n = 8) and gastrojejunostomy(n = 1).In one patient,the attempted colon pull-up failed due to extensive scarring of the mesocolon.The median follow up(following restoration of continuity of the gastrointestinal tract) was 36.5 mo.One patient developed dysphagia due to a stricture at the anastomotic site,which was successfully managed by dilatation.Another patient developed severe aspiration,necessitating laryngeal inlet closure and permanent tracheostomy,and 3 patients complained of occasional regurgitation.CONCLUSION:Management of severe corrosive injury involves prompt resuscitation and urgent surgical debridement.Although the subsequent restoration of continuity may be complicated and may not always be possible,long term outcomes are acceptable in the majority.展开更多
Esophagogastric stricture is the troublesome long-term complication of corrosive ingestion with a significant adverse impact on the quality of life.Surgery remains the mainstay of therapy in patients where endoscopic ...Esophagogastric stricture is the troublesome long-term complication of corrosive ingestion with a significant adverse impact on the quality of life.Surgery remains the mainstay of therapy in patients where endoscopic treatment is not feasible or fails to dilate the stricture.Conventional surgical management of esophageal stricture is open esophageal bypass using gastric or colon conduit.Colon is the commonly used esophageal substitute,particularly in those with high pharyngoesophageal strictures and in patients with accompanying gastric strictures.Traditionally colon bypass is performed using an open technique that requires a long midline incision from the xiphisternum to the suprapubic area,with adverse cosmetic outcomes and long-term complications like an incisional hernia.As most of the affected patients are in the second or third decade of life minimally invasive approach is an attractive proposition.However,minimally invasive surgery for corrosive esophagogastric stricture is slow to evolve due to the complex nature of the surgical procedure.With advancements in laparoscopic skills and instrumentation,the feasibility and safety of minimally invasive surgery in corrosive esophagogastric stricture have been documented.Initial series have mainly used a laparoscopic-assisted approach,whereas more recent studies have shown the safety of a total laparoscopic approach.The changing trend from laparoscopic assisted procedure to a totally minimally invasive technique for corrosive esophagogastric stricture should be carefully disseminated to preclude adverse longterm outcomes.Also,well-designed trials with long-term follow-ups are required to document the superiority of minimally invasive surgery for corrosive esophagogastric stricture.The present review focuses on the challenges and changing trends in the minimally invasive treatment of corrosive esophagogastric stricture.展开更多
An underground roadway usually contains defects of various types,and when the roadway is subjected to external loading,the locations of those defects influence the roadway by differing degrees.In this study,to study h...An underground roadway usually contains defects of various types,and when the roadway is subjected to external loading,the locations of those defects influence the roadway by differing degrees.In this study,to study how the locations of defects affect crack propagation in a roadway,specimens with tunnel-type voids were made using polymethyl methacrylate,and the stress wave produced by a bullet impacting an incident rod was used as the impact load.Meanwhile,the variations in crack speed,displacement,and dynamic stress intensity factor during crack propagation were obtained using an experimental system of digital laser dynamic caustics,and the commercial software ABAQUS was used for numerical simulations.From the experiments and numerical simulations,the crack propagation path was verified and the impact fracture behavior of a semicircular-arch roadway with different defect positions was presented.The results show that when the pre-fabricated crack is on the central axis of the sample,the crack propagation is purely mode I;when the pre-fabricated crack is 5 mm from the central axis,the crack propagation alternates between mode I and a mixture of modes I and II;when the pre-fabricated crack is at the edge of the semicircular-arch roadway,the crack propagation follows the I-II mixed mode.展开更多
基金The National Natural Science Foundation of China(No.51374210,51134025)the 111 Project(No.B14006)
文摘The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadruple inclusion and triangular inclusion） under lowvelocity impact loading. By recording the caustic spots of crack tips at different moments during the crack propagation, the variation regulations of dynamic stress intensity factors（ DSIF） and crack growth velocity with respect to time are obtained. The experimental results showthat the resistance effects to crack growth are varied with different shapes of inclusions in specimens, and the quadruple inclusion＇s effect is more apparent. The distortion degree of caustic spots is affected by the shapes of inclusions as well, and the situation is more serious for cylinder and quadruple inclusions. The overall values of DSIFs of triangular inclusion specimen are greater than the others, and the crack growth velocities, characteristic sizes and DSIFs showprocesses of fluctuations because of the disturbance of reflection waves in specimens. The results provide an experimental basis for the analysis of strength and impact-resistance ability in structures with deformity inclusions.
基金The Ph.D.Programs Foundation of Ministry of Education of China(No.20120023120020)the National Natural Science Foundation of China(No.51404273)
文摘The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.
基金provided by the National Natural Science Foundation of China (Nos. 51274204 and 51134025)National Key Basic Research Program (No. 2010CB732002)The Ministry of Education Program for New Century Excellent Talents to Support Project of China (No. NCET-12-0965)
文摘Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.
基金the support of the National Natural Science Foundation of China (Grant No.50774086 and 50874109)
文摘We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.
基金The project supported by the National Natural Science Foundation of Chinathe Scientific Commission of Yunnan Province of China
文摘Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are developed. The dynamic caustics are analyzed for the crack propagating along the interface between two bonded dissimilar materials. The variation of the caustic configurations is shown with the velocity change of the running crack and the ratio change of the stress intensity factors. Two characteristic dimensions are proposed that are not only practically measurable from optical caustic contours but also suitable to represent the behavior of transient caustics.
文摘The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a drop hammer system. Caustics information recorded in films illustrated the histories of both crack length and stress intensity factor. The dynamic fracture toughness and crack growth velocity of TA15ELI with lath-like microstructure were determined to be 279 MPa.m1/2 and 32.6 m/s, respectively. SEM fractograph analysis showed a mixed feature of mainly plastic mode for TA 15ELI alloy in dynamic mode-II fracture. Shear localization was observed in the vicinity of the crack initiation area.
文摘An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using reflected caustics in combination with the stress freezing and stress releasing technique. The results of this experimental method coincided favorably with the theoretical analysis results of Tweed and Rooke.
基金Key project from China Seismological Bureau (9691309020301)and State Natural Sciences Foundation of China (19732060 and 46764010
文摘Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area.
文摘In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics of drops with an equatorial radius a = 50 μm, 100 μm, 200 μm, and 500 μm are studied at the same drop/beam ratios (i.e. γ the ratio between the droplet equatorial radius and the Gaussian beam waist) using concentric illumination with a Gaussian beam, and the effect of droplet size on the optical caustics is analyzed. The curvature of the rainbow fringe and the evolution of the cusp caustics position, in this case, are obtained;the diameter range of droplet shape (ellipsoid) measured by Gaussian beam illumination is broadened. Based on this model, the effects of the relative positions d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics of the droplet when the center of the Gaussian beam deviates from the droplet center (the center of the Gaussian beam waist is on the same y-axis as the droplet center) are discussed. The optical caustics of the droplet when the center of the Gaussian beam is off the droplet center (the center of the Gaussian beam waist is on the z-axis with the droplet center) are also discussed. The effects of the relative positions of the center of the beam waist and the droplet center d = 0, 0.5y<sub>R</sub>, and y<sub>R</sub> on the optical caustics are also discussed. A method of measuring droplet shape with Gaussian beam illumination is proposed when the beam waist center is coaxial with the droplet center.
文摘Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at the University Hospital of Brazzaville. Patients and Methods: Prospective study was conducted from January 2014 to December 2015 in the Pediatric Departments of the UHB and centers of digestive endoscopy in Brazzaville. All children who ingested a caustic product and hospitalized were included after obtaining parental’s consent. The studied parameters were: Age, sex, nature and quantity of the caustic, the family’s attitude, clinical signs, endoscopic results according to Zagar’s classification, therapeutic modalities and evolution. Results: 8292 children were hospitalized and 68 because of the ingestion of caustic, a frequency of 0.8%. The average age was 23.6 months [2 months - 16 years]. The male sex was predominant (57.4%). Ingestion was accidental in 88.2% and voluntary in 11.8%. Factors favoring ingestion were storage methods (81.5%) and parental’s inattention or negligence (10.8%). Bleach was the most incriminated caustic (54.4%) followed by caustic soda (29.4%). The estimated quantity ingested was assumed to be minimal in 61.7%. Unsuitable acts were practiced by the family before the medical consultation in 66.1%. The dominant symptoms were digestive (47%) and neurological (25%). The average time to perform endoscopy was 48 hours in 88.2%. Endoscopy revealed lesions in 51.7%, the different stages were I (12 cases), II (16 cases) and III (3 cases). The mains factors of gravity were inappropriate gestures (85%) and the non-respect of the fasting (9%). Proton pump inhibitors were used in 50%. The evolution was favorable for in 73.5%. Conclusion: Ingestion of caustics by children is most often accidental favored by the inadequate packaging and storage. Prevention is about educating people in order to reduce their frequency.
基金Project supported by the European Union and the European Social Fund(No.EFOP-3.6.3-VEKOP-16-2017-00002).Open Access funding provided by European Union and the European Social Fund。
文摘While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors.These caustic surfaces,described in a closed form,are also developable surfaces of the same type as the original mirror surface.We provide efficient,algorithmic computation to find the caustic surface of each of the three types of developable surfaces(cone,cylinder,and tangent surface of a spatial curve).We also provide a potential application of the results in contemporary free-form architecture design.
基金The National Basic Research Program of China(973 Program)(No.2011CB606105)the National Natural Science Foundation of China(No.51374210,51134025)
文摘The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic caustic method. The experimental results indicate that the fluctuation of crack propagation velocity v first increases and then decreases in the crack propagation process. During the process of crack propagating into the inclusion area, the fracture resistance effect of the circular inclusion is the most significant and the effects of triangular and square inclusions are less obvious. The stress intensity factor near the crack tip increases during the propagation process and reaches its maximum value when the crack tip is close to the inclusions. The crack tip’s dynamic stress intensity factor （ DSIF） decreases when the crack exceeds the middle area of the double inclusions. These results provide an experimental basis and scientific foundation to strengthen the evaluation and fracture analysis of the structure containing deformity inclusions.
文摘Caustic ingestion is a relatively rare but potentially catastrophic gastroentero-logical emergency.Upper gastrointestinal(GI)endoscopy is currently regarded as the gold standard modality not only to assess the depth and the extension of GI caustic injury,but also to guide the appropriate treatment.Intriguingly,contrast-enhanced computed tomography(CECT)has recently emerged as a promising non-invasive and more accurate alternative to endoscopy in this setting.However,to date,evidence concerning the role of CECT as an alternative or complementary diagnostic tool to endoscopy in caustic ingestion is still limited.The aim of our review was to summarize and discuss the current evidence concerning the role of CECT in the emergency diagnosis of caustic ingestion and its value in assessing injury severity among non-pediatric patients.
文摘Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic endoscopy practice, explaining use of traditional as well as new and innovative techniques, for diagnosis and treatment of diseases in the paediatric upper gastrointestinal tract.
基金supported by the National Natural Science Foundation of China (No.10672002).
文摘The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carried out for two loading rates. By measuring the characteristic dimensions of the shadow spots during the caustic experiments, the dynamic SIFs are calculated for different loading rates. The experimental results indicate that the dynamic fracture toughness Kid increases remarkably with increasing loading rate, and the crack grows faster under the high-velocity impact. Moreover, by examining the crack growth routes and the fracture surfaces, it is shown that the loading rate also greatly affects the failure mechanisms at micro-scale.
基金The project supported by the National Natural Science Foundation of Chinathe Scientific Commussion of Yunnan Province of China
文摘Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.
文摘AIM:To report our experience in the surgical management of severe injuries of the gastrointestinal tract due to corrosive ingestion.METHODS:A retrospective review of patients who underwent emergency surgery for severe gastrointestinal injuries following corrosive ingestion between 1983 and 2010 was carried out.Data was extracted from a prospectively maintained esophageal disease database.Severe corrosive injuries were defined as full thickness necrosis with perforation of the esophagus or the stomach(with or without involvement of the adjacent viscera) with resultant mediastinitis or peritonitis.RESULTS:Between 1983 and 2010,209 patients with corrosive injury of the esophagus were managed.Of these,13(6.2%) patients underwent emergency surgery for severe corrosive injury.The median age of the patients was 22 years and the median interval between ingestion of the corrosive substance and surgery was 24 h.The surgical procedures done included esophagogastrectomy alone(n = 6),esophagogastrectomy withduodenectomy(n = 4),esophagogastrectomy with pancreaticoduodenectomy(n = 1),esophagogastrectomy with splenectomy(n = 1) and distal gastrectomy with duodenectomy(n = 1).Two patients died in the postoperative period and one after discharge awaiting the second surgery.The factors significantly predictive of mortality following such an injury included renal failure at the time of initial presentation,presence of metabolic acidosis,delay of more than 24 h between corrosive ingestion and surgery,and corrosive induced adjacent organ injury(pancreatic)(P < 0.001,0.02,0.005 and 0.015 respectively).Ten patients underwent subsequent surgery for restoration of the alimentary tract continuity with a colonic pull-up(n = 8) and gastrojejunostomy(n = 1).In one patient,the attempted colon pull-up failed due to extensive scarring of the mesocolon.The median follow up(following restoration of continuity of the gastrointestinal tract) was 36.5 mo.One patient developed dysphagia due to a stricture at the anastomotic site,which was successfully managed by dilatation.Another patient developed severe aspiration,necessitating laryngeal inlet closure and permanent tracheostomy,and 3 patients complained of occasional regurgitation.CONCLUSION:Management of severe corrosive injury involves prompt resuscitation and urgent surgical debridement.Although the subsequent restoration of continuity may be complicated and may not always be possible,long term outcomes are acceptable in the majority.
文摘Esophagogastric stricture is the troublesome long-term complication of corrosive ingestion with a significant adverse impact on the quality of life.Surgery remains the mainstay of therapy in patients where endoscopic treatment is not feasible or fails to dilate the stricture.Conventional surgical management of esophageal stricture is open esophageal bypass using gastric or colon conduit.Colon is the commonly used esophageal substitute,particularly in those with high pharyngoesophageal strictures and in patients with accompanying gastric strictures.Traditionally colon bypass is performed using an open technique that requires a long midline incision from the xiphisternum to the suprapubic area,with adverse cosmetic outcomes and long-term complications like an incisional hernia.As most of the affected patients are in the second or third decade of life minimally invasive approach is an attractive proposition.However,minimally invasive surgery for corrosive esophagogastric stricture is slow to evolve due to the complex nature of the surgical procedure.With advancements in laparoscopic skills and instrumentation,the feasibility and safety of minimally invasive surgery in corrosive esophagogastric stricture have been documented.Initial series have mainly used a laparoscopic-assisted approach,whereas more recent studies have shown the safety of a total laparoscopic approach.The changing trend from laparoscopic assisted procedure to a totally minimally invasive technique for corrosive esophagogastric stricture should be carefully disseminated to preclude adverse longterm outcomes.Also,well-designed trials with long-term follow-ups are required to document the superiority of minimally invasive surgery for corrosive esophagogastric stricture.The present review focuses on the challenges and changing trends in the minimally invasive treatment of corrosive esophagogastric stricture.
基金This work was financed by the State Key Development Program for Basic Research of China(2016YFC0600903)the National Natural Science Foundation of China(51774287).
文摘An underground roadway usually contains defects of various types,and when the roadway is subjected to external loading,the locations of those defects influence the roadway by differing degrees.In this study,to study how the locations of defects affect crack propagation in a roadway,specimens with tunnel-type voids were made using polymethyl methacrylate,and the stress wave produced by a bullet impacting an incident rod was used as the impact load.Meanwhile,the variations in crack speed,displacement,and dynamic stress intensity factor during crack propagation were obtained using an experimental system of digital laser dynamic caustics,and the commercial software ABAQUS was used for numerical simulations.From the experiments and numerical simulations,the crack propagation path was verified and the impact fracture behavior of a semicircular-arch roadway with different defect positions was presented.The results show that when the pre-fabricated crack is on the central axis of the sample,the crack propagation is purely mode I;when the pre-fabricated crack is 5 mm from the central axis,the crack propagation alternates between mode I and a mixture of modes I and II;when the pre-fabricated crack is at the edge of the semicircular-arch roadway,the crack propagation follows the I-II mixed mode.
