The fracture behaviours and notch effects of single-edge-notched(SEN)and double-edge-notched(DEN)2D carbon fibre reinforced carbon matrix composites(C/Cs)were discussed and compared.The fracture behaviours of DEN and ...The fracture behaviours and notch effects of single-edge-notched(SEN)and double-edge-notched(DEN)2D carbon fibre reinforced carbon matrix composites(C/Cs)were discussed and compared.The fracture behaviours of DEN and SEN were performed by tensile and bending load-displacement relationships,and the effects of notch depth on notch sensitivity were determined by DEN specimens.The results from mechanical tests indicated that the SEN exhibited a brittle behaviour with linear elasticity,while the DEN exhibited a ductile behaviour with nonlinearity.It was also found that increasing notch depth and decreasing ligament width can lead to a higher ultimate tensile strength of DEN.On the other hand,the digital image correlation(DIC)method and acoustic emission(AE)system were also applied during the mechanical tests to study the local mechanical characteristics of shear damage,strain concentration and fracture behaviour of 2D C/Cs.The results revealed the mechanisms of notch insensitivity and explained the differences in fracture behaviours between SEN and DEN.展开更多
In this study, the optimal weight designs of steel truss towers are determined, considering the notch effect. Thus, the impact of discontinuities in the cross-sections of steel elements on the total weight of the stru...In this study, the optimal weight designs of steel truss towers are determined, considering the notch effect. Thus, the impact of discontinuities in the cross-sections of steel elements on the total weight of the structure is revealed. For this purpose, the optimal weight designs of different truss towers analyzed by other researchers in previous years are reexamined using Particle Swarm Optimization and Firefly Algorithm. The main program where finite element analyses and optimization algorithms are encoded has been developed in MATLAB. Displacement, stress, geometric, and section height constraints are used in optimization methods. The effectiveness of these methods has been demonstrated by comparing both the results in the literature and with each other under un-notched conditions. Subsequently, considering the notch effect on the tension bar with the highest stress capacity in each structure, the impact of stress concentration on the minimum weight sizing of the structure is investigated using these proven methods. When the analysis results of both cases are examined, it is observed that the optimum weights of all structures under the notch effect have slightly increased. The stress concentration around the notch severely raises the nominal stress in the cross-section. In this case, the cross-section becomes insufficient due to the overcapacity, requiring larger profiles. The structure’s weight shows an increasing trend depending on the number of notched elements and the severity of stress concentration. Additionally, SAP2000 software is utilized for numerical simulations of the structures under identical conditions, enhancing the research content and providing further support for the comprehensive design optimization analyses. Consequently, minimizing the adverse effects of notches through careful material selection, proper manufacturing and assembly techniques, and regular maintenance is essential. The effects of notches should be considered in structural analysis and design, with measures taken to mitigate these effects when necessary.展开更多
Floating offshore wind turbine platforms typically use stiffened tubular joints at the connections between columns and braces.These joints are prone to fatigue due to complex weld geometries and the additional stress ...Floating offshore wind turbine platforms typically use stiffened tubular joints at the connections between columns and braces.These joints are prone to fatigue due to complex weld geometries and the additional stress concentrations caused by the stiffeners.Existing hot-spot stress approaches may be inadequate for analysing these joints because they do not simultaneously address weld-toe and weld-root failures.To address these limitations,this study evaluates the fatigue strength of stiffened tubular joints using the effective notch strain approach and the structural strain approach.Both methods account for fatigue at the weld toe and weld root and can be applied to both low-cycle fatigue(LCF)and high-cycle fatigue(HCF)regimes.Reanalyzes of a series of fatigue-tested specimens confirm the effectiveness of both approaches.The stiffener-shell fillet weld root is identified as the most critical fatigue location,which is consistent with fractographic observations.Although the brace-to-shell weld root exhibits lower stress levels in finite element(FE)models,weld quality was determined to be a crucial factor in fatigue failure.Furthermore,the results emphasise the importance of material plasticity in the LCF regime and demonstrate that full weld penetration significantly enhances fatigue strength.These findings provide valuable insights for the fatigue design of stiffened tubular joints in floating offshore wind turbine platforms.展开更多
Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of ...Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of load carrying cruciform joints inships is investigated using Effective Notch Stress (ENS) approach. A fictitious notch of 1 mm radius is introduced at theweld root and toe and fatigue stress is evaluated. The effect of weld leg length (l) and weld penetration depth (p) on ENS atweld root and toe are determined. The critical weld leg length (lcr) at which fatigue failure transitions from weld root toweld toe is investigated. An approximation formula for determination of the critical weld leg length considering weldpenetration depth (p) is proposed.展开更多
深反应离子刻蚀(DRIE)工艺在目前的硅微机械高深宽比结构加工中应用十分广泛。在SOI硅片DRIE刻蚀过程中,存在着一些被认为对刻蚀速率和结构轮廓不利的效应,如横向刻蚀(Notching)效应。通过在结构旁布置牺牲结构-硅岛,利用Notching效应...深反应离子刻蚀(DRIE)工艺在目前的硅微机械高深宽比结构加工中应用十分广泛。在SOI硅片DRIE刻蚀过程中,存在着一些被认为对刻蚀速率和结构轮廓不利的效应,如横向刻蚀(Notching)效应。通过在结构旁布置牺牲结构-硅岛,利用Notching效应加工出以悬空硅作为敏感单元的风速仪,其响应时间常数和电阻温度系数TCR(Temperature Coefficient of Resistant)分别为1.08μs和4 738×10-6/℃。正如所描述的,对于特定的微机械应用,Notching效应可以转变为一种加工优势,提高了微加工过程中的变化性。展开更多
A series of low cycle fatigue and creepfatigue tests on smooth specimens and notched specimens were performed with a high temperature alloy used in the manufacture of aeroengine turbine discs. The cyclic stressstrain ...A series of low cycle fatigue and creepfatigue tests on smooth specimens and notched specimens were performed with a high temperature alloy used in the manufacture of aeroengine turbine discs. The cyclic stressstrain behavior and fracture characteristics of the notched specimens were emphatically investigated. A comparison of fatigue behavior between smooth and notched specimens was done and lifetime of notched specimens was evaluated. At the same temperature, the fatiguecreep lives of the smooth specimens are far greater than that of the notched specimens.展开更多
An interesting phenomenon of dual S-N fatigue behavior is investigated in a metastable β titanium alloy,Ti-7 Mo-3 Nb-3 Cr-3 Al notched cylindrical specimens with an elastic stress concentration factor of Kt=3.Fractog...An interesting phenomenon of dual S-N fatigue behavior is investigated in a metastable β titanium alloy,Ti-7 Mo-3 Nb-3 Cr-3 Al notched cylindrical specimens with an elastic stress concentration factor of Kt=3.Fractographic studies revealed all specimens,and irrespective of lifetime,failed from the specimen surface because of stress concentration occurs at the notch root.Typically,the short-life-distribution is usually associated with surface-failure-without-facets and the long-life-distribution generally occurs due to surface-failure-with-facets.This competing failure leads to increasing the variability in fatigue lifetime and further facilitates the difficulty in prediction of fatigue lifetime.Crack-initiation area characterization was conducted by using mechanical grinding,focused ion beam milling and subsequent electron backscattered diffraction(EBSD) analysis of the 2 D section across faceted grains.Results show that the α_p particles(especially the elongated α_p particles) well-oriented for basal slip activation is a preferential fatigue-critical microstructural configuration.Additionally,the β+α_s matrix has a higher KAM value than the α_p particles in fatigued microstructures and significant dislocation activity in the form of dislocation tangles is observed in α_p boundaries.展开更多
In engineering applications,the notch effect and size effect significantly influence the evaluation of fatigue performance in components,necessitating special attention in life prediction.This study proposes a new pro...In engineering applications,the notch effect and size effect significantly influence the evaluation of fatigue performance in components,necessitating special attention in life prediction.This study proposes a new probabilistic model,based on the theory of critical distance(TCD),to predict fatigue life,with the aim of quantitatively assessing the impact of notch effect and size effect.The stress distribution on the critical plane is first characterized using a sixth-order multinomial function,and the relative stress gradient function is utilized to calculate the value of the critical distance.Furthermore,the effect of the ratio of shear strain to normal strain on fatigue life under multiaxial loading is considered.Additionally,the integration of the Weibull distribution into the TCD is employed for conducting probabilistic modeling of fatigue life.Finally,fatigue experiments are conducted on notched specimens of Q355D steel,demonstrating that the life prediction results under 50%survival probability are superior to the traditional TCD method.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.52072356 and 52032011)。
文摘The fracture behaviours and notch effects of single-edge-notched(SEN)and double-edge-notched(DEN)2D carbon fibre reinforced carbon matrix composites(C/Cs)were discussed and compared.The fracture behaviours of DEN and SEN were performed by tensile and bending load-displacement relationships,and the effects of notch depth on notch sensitivity were determined by DEN specimens.The results from mechanical tests indicated that the SEN exhibited a brittle behaviour with linear elasticity,while the DEN exhibited a ductile behaviour with nonlinearity.It was also found that increasing notch depth and decreasing ligament width can lead to a higher ultimate tensile strength of DEN.On the other hand,the digital image correlation(DIC)method and acoustic emission(AE)system were also applied during the mechanical tests to study the local mechanical characteristics of shear damage,strain concentration and fracture behaviour of 2D C/Cs.The results revealed the mechanisms of notch insensitivity and explained the differences in fracture behaviours between SEN and DEN.
文摘In this study, the optimal weight designs of steel truss towers are determined, considering the notch effect. Thus, the impact of discontinuities in the cross-sections of steel elements on the total weight of the structure is revealed. For this purpose, the optimal weight designs of different truss towers analyzed by other researchers in previous years are reexamined using Particle Swarm Optimization and Firefly Algorithm. The main program where finite element analyses and optimization algorithms are encoded has been developed in MATLAB. Displacement, stress, geometric, and section height constraints are used in optimization methods. The effectiveness of these methods has been demonstrated by comparing both the results in the literature and with each other under un-notched conditions. Subsequently, considering the notch effect on the tension bar with the highest stress capacity in each structure, the impact of stress concentration on the minimum weight sizing of the structure is investigated using these proven methods. When the analysis results of both cases are examined, it is observed that the optimum weights of all structures under the notch effect have slightly increased. The stress concentration around the notch severely raises the nominal stress in the cross-section. In this case, the cross-section becomes insufficient due to the overcapacity, requiring larger profiles. The structure’s weight shows an increasing trend depending on the number of notched elements and the severity of stress concentration. Additionally, SAP2000 software is utilized for numerical simulations of the structures under identical conditions, enhancing the research content and providing further support for the comprehensive design optimization analyses. Consequently, minimizing the adverse effects of notches through careful material selection, proper manufacturing and assembly techniques, and regular maintenance is essential. The effects of notches should be considered in structural analysis and design, with measures taken to mitigate these effects when necessary.
基金supported by the National Natural Science Foundation of China(Grant No.52101350).
文摘Floating offshore wind turbine platforms typically use stiffened tubular joints at the connections between columns and braces.These joints are prone to fatigue due to complex weld geometries and the additional stress concentrations caused by the stiffeners.Existing hot-spot stress approaches may be inadequate for analysing these joints because they do not simultaneously address weld-toe and weld-root failures.To address these limitations,this study evaluates the fatigue strength of stiffened tubular joints using the effective notch strain approach and the structural strain approach.Both methods account for fatigue at the weld toe and weld root and can be applied to both low-cycle fatigue(LCF)and high-cycle fatigue(HCF)regimes.Reanalyzes of a series of fatigue-tested specimens confirm the effectiveness of both approaches.The stiffener-shell fillet weld root is identified as the most critical fatigue location,which is consistent with fractographic observations.Although the brace-to-shell weld root exhibits lower stress levels in finite element(FE)models,weld quality was determined to be a crucial factor in fatigue failure.Furthermore,the results emphasise the importance of material plasticity in the LCF regime and demonstrate that full weld penetration significantly enhances fatigue strength.These findings provide valuable insights for the fatigue design of stiffened tubular joints in floating offshore wind turbine platforms.
文摘Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of load carrying cruciform joints inships is investigated using Effective Notch Stress (ENS) approach. A fictitious notch of 1 mm radius is introduced at theweld root and toe and fatigue stress is evaluated. The effect of weld leg length (l) and weld penetration depth (p) on ENS atweld root and toe are determined. The critical weld leg length (lcr) at which fatigue failure transitions from weld root toweld toe is investigated. An approximation formula for determination of the critical weld leg length considering weldpenetration depth (p) is proposed.
文摘深反应离子刻蚀(DRIE)工艺在目前的硅微机械高深宽比结构加工中应用十分广泛。在SOI硅片DRIE刻蚀过程中,存在着一些被认为对刻蚀速率和结构轮廓不利的效应,如横向刻蚀(Notching)效应。通过在结构旁布置牺牲结构-硅岛,利用Notching效应加工出以悬空硅作为敏感单元的风速仪,其响应时间常数和电阻温度系数TCR(Temperature Coefficient of Resistant)分别为1.08μs和4 738×10-6/℃。正如所描述的,对于特定的微机械应用,Notching效应可以转变为一种加工优势,提高了微加工过程中的变化性。
文摘A series of low cycle fatigue and creepfatigue tests on smooth specimens and notched specimens were performed with a high temperature alloy used in the manufacture of aeroengine turbine discs. The cyclic stressstrain behavior and fracture characteristics of the notched specimens were emphatically investigated. A comparison of fatigue behavior between smooth and notched specimens was done and lifetime of notched specimens was evaluated. At the same temperature, the fatiguecreep lives of the smooth specimens are far greater than that of the notched specimens.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0701303)National Natural Science Foundation of China (No. 51801156)Natural Science Basic Research Plan in Shaanxi Province of China (No. 2019JM-584)。
文摘An interesting phenomenon of dual S-N fatigue behavior is investigated in a metastable β titanium alloy,Ti-7 Mo-3 Nb-3 Cr-3 Al notched cylindrical specimens with an elastic stress concentration factor of Kt=3.Fractographic studies revealed all specimens,and irrespective of lifetime,failed from the specimen surface because of stress concentration occurs at the notch root.Typically,the short-life-distribution is usually associated with surface-failure-without-facets and the long-life-distribution generally occurs due to surface-failure-with-facets.This competing failure leads to increasing the variability in fatigue lifetime and further facilitates the difficulty in prediction of fatigue lifetime.Crack-initiation area characterization was conducted by using mechanical grinding,focused ion beam milling and subsequent electron backscattered diffraction(EBSD) analysis of the 2 D section across faceted grains.Results show that the α_p particles(especially the elongated α_p particles) well-oriented for basal slip activation is a preferential fatigue-critical microstructural configuration.Additionally,the β+α_s matrix has a higher KAM value than the α_p particles in fatigued microstructures and significant dislocation activity in the form of dislocation tangles is observed in α_p boundaries.
基金supported by the National Natural Science Foundation of China(Grant Number 52365016)Gansu Province Young Doctor Fund Project(Grant Number 2023QB-030)Lanzhou University of Technology Graduate Research Exploration Project.
文摘In engineering applications,the notch effect and size effect significantly influence the evaluation of fatigue performance in components,necessitating special attention in life prediction.This study proposes a new probabilistic model,based on the theory of critical distance(TCD),to predict fatigue life,with the aim of quantitatively assessing the impact of notch effect and size effect.The stress distribution on the critical plane is first characterized using a sixth-order multinomial function,and the relative stress gradient function is utilized to calculate the value of the critical distance.Furthermore,the effect of the ratio of shear strain to normal strain on fatigue life under multiaxial loading is considered.Additionally,the integration of the Weibull distribution into the TCD is employed for conducting probabilistic modeling of fatigue life.Finally,fatigue experiments are conducted on notched specimens of Q355D steel,demonstrating that the life prediction results under 50%survival probability are superior to the traditional TCD method.
