Iron （Fe） has a low solid solubility in aluminum （Al）, and it usually forms Fe-rich intermetallic compounds. Scandium （Sc） is an element that can act as a grain refiner, modify the eutectic silicon and change th...Iron （Fe） has a low solid solubility in aluminum （Al）, and it usually forms Fe-rich intermetallic compounds. Scandium （Sc） is an element that can act as a grain refiner, modify the eutectic silicon and change the morphology of Fe-rich intermetallic compounds at the same time. The present work was conducted to study the effect of Sc on the mechanical properties of Al-7Si-0.3Mg. The alloy was prepared by squeeze casting at two levels of Fe （0.2 and 0.4 wt%） and three levels of Sc （0 wt%, 0.2 wt% and 0.4 wt%）. Sc is found to increase the mechanical properties of the alloy, including its hardness, yield strength and ultimate tensile strength. At 0.2 wt% Fe, adding Sc increases the strength while maintaining good elongation. At 0.4 wt% Fe, adding Sc increases the strength but decreases the elongation slightly. The distributions and morphologies of intermetallic compounds and eutectic silicon affect the elongation. Both Fe-rich intermetallic compounds and Sc-rich intermetallic compounds act as crack initiation sites. The 0.2 wt% Fe ＋ 0.2 wt% Sc alloy has the lowest amount of these intermetallic compounds, and eutectic silicon is small and fibrous. So, it has the highest elongation.展开更多
The effect of Sc on precipitation hardening of AlSi6Mg was studied.Zr was previously reported that it increased the effectiveness of Sc in wrought aluminum in many areas so Zr was also used together with Sc in this st...The effect of Sc on precipitation hardening of AlSi6Mg was studied.Zr was previously reported that it increased the effectiveness of Sc in wrought aluminum in many areas so Zr was also used together with Sc in this study. Different levels of Sc and Zr additions were added to AlSi6Mg before casting in the permanent mold.The samples were precipitation hardened at different aging temperatures and for various aging time before testing for tensile strength and hardness.It was found that Sc addition into Al6SiMg can change its response to age hardening.Additions of Sc and Sc with Zr increased both yield strength and hardness for both aging temperatures.In addition,Sc was found to modify eutectic Si to obtain fibrous morphology.This effect of Sc on eutectic silicon modification has never been reported before.展开更多
This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that differ...This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.展开更多
FeNiCrCoSi_(x) and FeNiCrCoTi_(x)(x=0,0.3,0.6,and 0.9 wt.%)high entropy alloys(HEAs)were prepared via the powder metallurgy technique.A homogenous distribution of the elements in all alloys due to the formation of a s...FeNiCrCoSi_(x) and FeNiCrCoTi_(x)(x=0,0.3,0.6,and 0.9 wt.%)high entropy alloys(HEAs)were prepared via the powder metallurgy technique.A homogenous distribution of the elements in all alloys due to the formation of a solid solution phase is observed.The density and hardness of the prepared HEAs are improved by Si and Ti additions,compared to FeNiCrCo HEA.The wear rate of the prepared alloys was studied at different loads and the results indicate that the alloys that contain 0.3 wt.%Si and 0.9 wt.%Ti have the lowest wear rates.X-ray diffraction,SEM,and EDX were used to understand the phases,grain sizes,and microstructures in different investigated HEAs.The effects of Si and Ti content on the corrosion behavior and surface morphologies of sintered FeNiCrCoSi_(x) and FeNiCrCoTi_(x) HEAs were studied by immersion in H_(2)SO_(4),HNO_(3),and HCl solutions.Uniform corrosion and localized pitting are observed in different sizes in the corrosive media used.Because of the smaller pit size and the reduced pit density,the FeNiCrCoSi_(0.3) HEA has an excellent microstructure.展开更多
In laparoscopic surgery, the surgeons are equipped with the suitable tools for the surgery, while the laparoscope is used to capture the operation environment and displays it on a monitor. This paper presents the math...In laparoscopic surgery, the surgeons are equipped with the suitable tools for the surgery, while the laparoscope is used to capture the operation environment and displays it on a monitor. This paper presents the mathematical kinematic position modeling of the laparoscopic tools used for autonomous positioning of a laparoscope in such operations. These models are obtained using Denavit-Hartenberg (D-H) Notations and Homogenous Transformation Matrix (HTM). The laparoscopic tools are considered as six degrees of freedom (DOF) mechanisms while the laparoscope has four DOF. The 3D loop closure equation is used to obtain the laparoscope kinematic position models in terms of those of the laparoscopic tools. These models are used to simulate and align the laparoscope camera with the surgeon’s laparoscopic Tools Center Points (TCP). The obtained results show the smooth positioning of the laparoscope camera for better visu-alization of laparoscopic surgery environments.展开更多
In recent years,additive manufacturing(AM)has gained popularity in the aerospace,automobile,and medical industries due to its ability to produce complex profiles with minimal tolerances.Micro-milling is recommended fo...In recent years,additive manufacturing(AM)has gained popularity in the aerospace,automobile,and medical industries due to its ability to produce complex profiles with minimal tolerances.Micro-milling is recommended for machining AM-based parts to improve surface quality and form accuracy.Therefore,the machinability of a titanium alloy(Ti6Al4V)manufactured using selective laser melting(SLM)is explored and compared to that of wrought Ti6Al4V in micro-milling.The experimental results reveal the surface topology,chip morphology,burr formation,and tool wear characteristics of both samples.The micro-milling of AM-based Ti6Al4V generates a surface roughness of 19.2 nm,which is 13.9%lower than that of wrought workpieces,and this component exhibits less tool wear.SLM-based Ti6Al4V produces continuous chips,while wrought Ti6Al4V yields relatively short chips.Additionally,SLM-fabricated Ti6Al4V exhibits smaller burrs after micro-milling than wrought Ti6Al4V.Despite the higher hardness of SLM-based Ti6Al4V,it demonstrates better machinability than wrought Ti6Al4V,resulting in better surface quality with lower tool wear levels and shorter burr heights.This study provides valuable insights into future research on postprocessing AM-based titanium parts,especially using micro-milling.展开更多
Nickel Titanium alloy (Nitinol) is characterized by its good mechanical properties, good damping properties in addition to its distinctive shape-memory effect and superelasticity effect besides its great bio-mechanica...Nickel Titanium alloy (Nitinol) is characterized by its good mechanical properties, good damping properties in addition to its distinctive shape-memory effect and superelasticity effect besides its great bio-mechanical compatibility and corrosion resistance. These properties have empowered its applications, particularly within the bio-medical and aerospace industry. Despite these exceptional properties, the manufacturing of Nitinol by conventional methods is exceptionally troublesome and costly and consequently must be inspected. Therefore, additive manufacturing specifically laser-based ones were used recently. In this research, the effect of processing parameters of laser cladding/laser direct deposition on Nitinol’s Microstructure, Hardness and Clad Dimensions was evaluated. Systematic characterization of Nitinol samples was done utilizing Optical Microscopy and Vickers hardness tester. Samples of Nitinol were synthesized with different processing parameters using laser cladding and its properties were investigated and compared to one another to get the optimum processing parameters to synthesize a near net shape, fully dense Nitinol component with reliable properties. The results showed that there’s a processing parameter window at which the alloy possesses its best mechanical and functional properties which were of Laser power of value 1.25 Kw, Scan speed of 1.5 m/min and powder deposition rate of 1.5/1.5 RPM, these conditions resulted in the formation of martensite phase which is responsible for its functional properties with 40% volume fraction and a hardness value of 598 HV.展开更多
Microstructure development is well accepted to have a major effect on mechanical properties during its services. One of the most interesting ways to improve mechanical properties is to reduce secondary dendrite arm sp...Microstructure development is well accepted to have a major effect on mechanical properties during its services. One of the most interesting ways to improve mechanical properties is to reduce secondary dendrite arm spacing （SDAS）.SDAS also plays an important role in controlling and providing the well distributed and fine microstructure resulting in better tensile strength and elongation.To reduce SDAS,it is commonly known by increasing cooling rate and increasing interface instability by limited-soluble alloy addition.It is,however, unclear that how both cooling rate and limited-soluble alloy,e.g.Sb,relate to each other.This may be the reason that the limited-soluble alloy may not effectively reduce SDAS.To better understand this phenomenon, influences of Sb on solid/liquid interface instability using columnar to equiaxed transition （CET） were studied in the directionally solidification experiment.From macrographs and micrographs,it was observed that at 0.06-0.18 wt pct Sb the CET min,CET max,CET zone and %CET area gradually increased.The increases of CET max and CET zone in samples with 0.06 to 0.18 wt pct Sb addition results from recalesced zone.On the other hand,the variations of CET max and CET zone in samples with 0.24 to 0.30 wt pct Sb results from equiaxed grain formations that prohibit the growth of columnar grain and latent heat from intermetallic phase solidified.展开更多
This paper presents a multi-objective production planning model for a factory operating under a multi-product, and multi-period environment using the lexicographic (pre-emptive) procedure. The model objectives are to ...This paper presents a multi-objective production planning model for a factory operating under a multi-product, and multi-period environment using the lexicographic (pre-emptive) procedure. The model objectives are to maximize the profit, minimize the total cost, and maximize the Overall Service Level (OSL) of the customers. The system consists of three potential suppliers that serve the factory to serve three customers/distributors. The performance of the developed model is illustrated using a verification example. Discussion of the results proved the efficacy of the model. Also, the effect of the deviation percentages on the different objectives is discussed.展开更多
Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected...Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected by the boundaries between layers of different materials or same material but in different states （solid or liquid or gas）. This paper investigates the effects of ultrasound （US） on the surface of the solidified weld which has been subjected to ultrasonic vibrations of 20 kHz frequency during laser welding. Vibrations due to ultrasound normally exert a very high force which is usually hundred or thousand times the gravity. The transverse waves will also cause movement of molten material in the weld. As the surface of the weld beads were of interest and not the mechanical properties and the microstructure, investigation of bead on plate welds were found to be sufficient. High carbon steel plate was held at one end by the ultrasonic horn through which ultrasound was injected. A bead on plate weld using a CO2 laser （1 kW） was then performed along the center of the plate using three different welding speeds namely, 400, 1200 and 2000 mm per minute. The ultrasonic powers selected were 3 W and 6 W respectively for each welding speed as higher acoustical power was causing ejection of molten metal from the pool during welding. 3D surface measurements and analysis were then made on a section of length 20 mm using a Talysurf machine. The results show that the surface of the weld was affected to different extent depending on the positions being considered in the weld. Some regions were similar to the reference weld whereas some specific regions were heavily disrupted with deep valleys followed by high peak/s. This shows that US vibration of weld pools, even at very small acoustical power, is a more complex problem than other similar processes such as casting because of the very small volume of molten metal involved.展开更多
To attain an enhanced combination of mechanical properties for low alloyed steel, the current study has been made to fulfill that growing need in the industry. Its results are introduced within this paper. One step Qu...To attain an enhanced combination of mechanical properties for low alloyed steel, the current study has been made to fulfill that growing need in the industry. Its results are introduced within this paper. One step Quenching and Partitioning (Q&P) heat treatment has been applied on Niobium-based microalloyed steel alloy with 0.2 %C, in the form of 2 mm thickness sheets. The target of this study is to investigate the viability of applying that significantly recommended, results-wise, heat treatment on the highly well-suited alloy steel samples, to achieve the main target of enhanced properties. A single temperature of 275°C was used as quenching and Partitioning temperature. Four Partitioning periods (30, 200, 500, and 1000 Seconds) were used for soaking at the same temperature. The results were analyzed in the light of microstructural investigation and mechanical testing. All applied cycles did not enhance the strength but moderately improved the ductility and toughness, mainly caused by the slightly high soaking temperature used. Niobium impact of grain refining was apparent through all cycles. The cycle of 500 Seconds Partitioning time obtained optimum values at that particular temperature. The 1000 Seconds Cycle obtained the worst combination of properties. A set of recommendations are set. More research is required at this point, where a lower Partitioning temperature is advised. In the light of the applied combination of parameters, the Partitioning period at such temperature is advised to be between 500 and 1000 Seconds. A high probability that periods closer to 500 than 1000 Seconds will produce better results. More research is needed between those two values of Partitioning time to precisely determine the optimum time at that temperature on that specific alloy.展开更多
Form error measurement is a critical exercise in providing measures for the quality control in the precision manufacturing industry.Coordinate measuring machine （CMM） is one of the automated systems used in the accu...Form error measurement is a critical exercise in providing measures for the quality control in the precision manufacturing industry.Coordinate measuring machine （CMM） is one of the automated systems used in the accurate and precise dimensional measurements and geometrical form.This paper aims to study the effect of dynamic original unforeseeable errors at different undulations per revolution （UPR） of standard artifact measurement using selected two types of CMM touchtriggering stylus.Stylus-type and stylus-speed parameters were adopted and utilized throughout the course of experiment.The results are analyzed using fast Fourier transformation to obtain foreseeable geometrical errors due to CMM machine structure and stylus scanning speeds.The results of experiment successfully indicate that the number of UPR plays an important role in determining the CMM accuracy level of the roundness measurement result.Some specific error equations for stylus system and machine structure responses have been postulated and analysed to empirically predict the accuracy of PRISMOBridge-CMM-type at National Institute for Standards （NIS） in egypt.展开更多
In this study,we attempted to characterise the effects of date-palm fibre(DPF)and a date-palm fibre/sheep wool hybrid in polyester to enhance high-performance and low-cost composite materials that can be used in insul...In this study,we attempted to characterise the effects of date-palm fibre(DPF)and a date-palm fibre/sheep wool hybrid in polyester to enhance high-performance and low-cost composite materials that can be used in insulation building systems,automotive parts,and home furniture.The DPF was treated using 5%NaOH solution;and the sheep wool was cleaned with 50℃hot water and detergents.The composite specimens were prepared with different fibre contents(0%,10%,20%,30%(w))using a compression moulding technique.The effect of fibre reinforcement was analysed in terms of the mechanical properties(tensile,flexural,impact,and hardness)and composite density.Additionally,scanning electron microscopy(SEM)was performed on the fibres before and after treatment,and the fractured surfaces of all composite specimens were examined after tensile testing.The results showed that the 20%DPF/sheep wool hybrid reinforced polyester produced the best results.The ultimate tensile strength and modulus were 27 MPa and 3.69GPa,respectively.The ultimate flexural strength and flexural modulus were 35.4 and 2507 MPa,respectively.The impact strength was 39.5 kJ/m^(2)and the hardness was 64 HB.The density decreased to the lowest value of 1.02 g/cm^(3)with the 30%DPF/sheep wool hybrid.The SEM showed good adhesion and interfacial bonding between DPF/sheep wool hybrid fibres and the polyester matrix,particularly at 20%fibre content.展开更多
In this research study,Bambusa ssp,the utilized species of bamboo,was rendered into a more versatile construction material in the form of laminates.The laminated specimens were manufactured using simplified processing...In this research study,Bambusa ssp,the utilized species of bamboo,was rendered into a more versatile construction material in the form of laminates.The laminated specimens were manufactured using simplified processing methods according to the ASTM D3039 and ASTM D143 standards.Polyvinyl acetate was the adhesive used between the 2-ply laminate.The mechanical properties of the specimens were evaluated through tensile,compressive and bending strength tests according to set standards on the Testometric M500-50AT Universal Testing Machine.The tensile strength of laminated bamboo was comparable to that of redwood,spruce,cedar and pine.The ratio of compressive strength of parallel to perpendicularfibers in compressive tests was in a close range to that of poplar,fir and pine.The correlation in compressive strength values between bamboo and wood confirmed the inherent anisotropic nature of both plant materials.展开更多
Bamboo in its raw state is difficult to incorporate in complex structures due to its tubular shape. In this research article, a novel approach to connect bamboo was designed and evaluated in order to integrate sustain...Bamboo in its raw state is difficult to incorporate in complex structures due to its tubular shape. In this research article, a novel approach to connect bamboo was designed and evaluated in order to integrate sustainable material into modern structures. Several bamboo joints for culm connection were designed based on strength and durability under various loading capacity. The conceptual joints were manufactured and subjected to destructive testing on the Universal Testing Machine, Testometric M500-50AT. From the mechanical properties generated, final modifications and refinements were incorporated into the joint design. Self-drilling metal screw joints were found to be the strongest with a maximum resisting force of around 11 kN in compression and 10 kN in tension. Riveted joints were the second strongest joint, while tightening ring joints, the weakest among the three, could only resist a peak load of 747 N in tension. The joints, designed with metal fittings, proved to be more practical for utilization in assembly design.展开更多
The study examines the impact of microstructure and polymethyl methacrylate(PMMA)grafting on the degradability of Zn–Mg alloys.The mechanical properties ofa Zn alloy containing 0.68 wt%Mg and extruded at 200◦C are en...The study examines the impact of microstructure and polymethyl methacrylate(PMMA)grafting on the degradability of Zn–Mg alloys.The mechanical properties ofa Zn alloy containing 0.68 wt%Mg and extruded at 200◦C are enhanced for degradable load-bearing applications,addressing a crucial need in the field.The materialexhibits a bimodal grain size distribution that is random texture,consisting of secondary phases,grains,and sub-grains.With an elongation to failure of 16%,theyield and ultimate tensile strengths are 325.9 and 414.5 MPa,respectively,and the compressive yield strength is 450.5 MPa.The“grafting-from”method was used to coat a few micrometers thick of PMMA on both bulk and scaffold Zn alloys to mitigate the corrosion rate.The last one is aporous structure,with a porosity of 65.8%,considered as in the first approach of an orthopedic implant.After being immersed for 720 h,the PMMA-grafted bulkalloy’s corrosion rate decreased from 0.43 to 0.25 mm/y.Similarly,the scaffold alloy’s corrosion rate reduced from 1.24 to 0.49 mm/y.These results indicate that themethod employed could be used for future orthopedic applications.展开更多
基金financially supported by the Royal Golden Jubilee Ph.D.Program (No.PHD/0285/2552)the King Mongkut's University of Technology Thonburi,National Metal and Materials Technology Center (No.MT-B-58-MET-07-265-I)
文摘Iron （Fe） has a low solid solubility in aluminum （Al）, and it usually forms Fe-rich intermetallic compounds. Scandium （Sc） is an element that can act as a grain refiner, modify the eutectic silicon and change the morphology of Fe-rich intermetallic compounds at the same time. The present work was conducted to study the effect of Sc on the mechanical properties of Al-7Si-0.3Mg. The alloy was prepared by squeeze casting at two levels of Fe （0.2 and 0.4 wt%） and three levels of Sc （0 wt%, 0.2 wt% and 0.4 wt%）. Sc is found to increase the mechanical properties of the alloy, including its hardness, yield strength and ultimate tensile strength. At 0.2 wt% Fe, adding Sc increases the strength while maintaining good elongation. At 0.4 wt% Fe, adding Sc increases the strength but decreases the elongation slightly. The distributions and morphologies of intermetallic compounds and eutectic silicon affect the elongation. Both Fe-rich intermetallic compounds and Sc-rich intermetallic compounds act as crack initiation sites. The 0.2 wt% Fe ＋ 0.2 wt% Sc alloy has the lowest amount of these intermetallic compounds, and eutectic silicon is small and fibrous. So, it has the highest elongation.
文摘The effect of Sc on precipitation hardening of AlSi6Mg was studied.Zr was previously reported that it increased the effectiveness of Sc in wrought aluminum in many areas so Zr was also used together with Sc in this study. Different levels of Sc and Zr additions were added to AlSi6Mg before casting in the permanent mold.The samples were precipitation hardened at different aging temperatures and for various aging time before testing for tensile strength and hardness.It was found that Sc addition into Al6SiMg can change its response to age hardening.Additions of Sc and Sc with Zr increased both yield strength and hardness for both aging temperatures.In addition,Sc was found to modify eutectic Si to obtain fibrous morphology.This effect of Sc on eutectic silicon modification has never been reported before.
文摘This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.
文摘FeNiCrCoSi_(x) and FeNiCrCoTi_(x)(x=0,0.3,0.6,and 0.9 wt.%)high entropy alloys(HEAs)were prepared via the powder metallurgy technique.A homogenous distribution of the elements in all alloys due to the formation of a solid solution phase is observed.The density and hardness of the prepared HEAs are improved by Si and Ti additions,compared to FeNiCrCo HEA.The wear rate of the prepared alloys was studied at different loads and the results indicate that the alloys that contain 0.3 wt.%Si and 0.9 wt.%Ti have the lowest wear rates.X-ray diffraction,SEM,and EDX were used to understand the phases,grain sizes,and microstructures in different investigated HEAs.The effects of Si and Ti content on the corrosion behavior and surface morphologies of sintered FeNiCrCoSi_(x) and FeNiCrCoTi_(x) HEAs were studied by immersion in H_(2)SO_(4),HNO_(3),and HCl solutions.Uniform corrosion and localized pitting are observed in different sizes in the corrosive media used.Because of the smaller pit size and the reduced pit density,the FeNiCrCoSi_(0.3) HEA has an excellent microstructure.
文摘In laparoscopic surgery, the surgeons are equipped with the suitable tools for the surgery, while the laparoscope is used to capture the operation environment and displays it on a monitor. This paper presents the mathematical kinematic position modeling of the laparoscopic tools used for autonomous positioning of a laparoscope in such operations. These models are obtained using Denavit-Hartenberg (D-H) Notations and Homogenous Transformation Matrix (HTM). The laparoscopic tools are considered as six degrees of freedom (DOF) mechanisms while the laparoscope has four DOF. The 3D loop closure equation is used to obtain the laparoscope kinematic position models in terms of those of the laparoscopic tools. These models are used to simulate and align the laparoscope camera with the surgeon’s laparoscopic Tools Center Points (TCP). The obtained results show the smooth positioning of the laparoscope camera for better visu-alization of laparoscopic surgery environments.
基金Supported by the Research Grants Council of the Hong Kong Special Administrative Region of China(Grant No.15221322)National Natural Science Foundation of China(Grant No.U19A20104)+1 种基金Shenzhen Municipal Science and Technology Program(Grant No.JCYJ20210324131214039)State Key Laboratory of Ultra-precision Machining Technology and the Research Committee of The Hong Kong Polytechnic University of China(Project Code:RHD5)。
文摘In recent years,additive manufacturing(AM)has gained popularity in the aerospace,automobile,and medical industries due to its ability to produce complex profiles with minimal tolerances.Micro-milling is recommended for machining AM-based parts to improve surface quality and form accuracy.Therefore,the machinability of a titanium alloy(Ti6Al4V)manufactured using selective laser melting(SLM)is explored and compared to that of wrought Ti6Al4V in micro-milling.The experimental results reveal the surface topology,chip morphology,burr formation,and tool wear characteristics of both samples.The micro-milling of AM-based Ti6Al4V generates a surface roughness of 19.2 nm,which is 13.9%lower than that of wrought workpieces,and this component exhibits less tool wear.SLM-based Ti6Al4V produces continuous chips,while wrought Ti6Al4V yields relatively short chips.Additionally,SLM-fabricated Ti6Al4V exhibits smaller burrs after micro-milling than wrought Ti6Al4V.Despite the higher hardness of SLM-based Ti6Al4V,it demonstrates better machinability than wrought Ti6Al4V,resulting in better surface quality with lower tool wear levels and shorter burr heights.This study provides valuable insights into future research on postprocessing AM-based titanium parts,especially using micro-milling.
文摘Nickel Titanium alloy (Nitinol) is characterized by its good mechanical properties, good damping properties in addition to its distinctive shape-memory effect and superelasticity effect besides its great bio-mechanical compatibility and corrosion resistance. These properties have empowered its applications, particularly within the bio-medical and aerospace industry. Despite these exceptional properties, the manufacturing of Nitinol by conventional methods is exceptionally troublesome and costly and consequently must be inspected. Therefore, additive manufacturing specifically laser-based ones were used recently. In this research, the effect of processing parameters of laser cladding/laser direct deposition on Nitinol’s Microstructure, Hardness and Clad Dimensions was evaluated. Systematic characterization of Nitinol samples was done utilizing Optical Microscopy and Vickers hardness tester. Samples of Nitinol were synthesized with different processing parameters using laser cladding and its properties were investigated and compared to one another to get the optimum processing parameters to synthesize a near net shape, fully dense Nitinol component with reliable properties. The results showed that there’s a processing parameter window at which the alloy possesses its best mechanical and functional properties which were of Laser power of value 1.25 Kw, Scan speed of 1.5 m/min and powder deposition rate of 1.5/1.5 RPM, these conditions resulted in the formation of martensite phase which is responsible for its functional properties with 40% volume fraction and a hardness value of 598 HV.
文摘Microstructure development is well accepted to have a major effect on mechanical properties during its services. One of the most interesting ways to improve mechanical properties is to reduce secondary dendrite arm spacing （SDAS）.SDAS also plays an important role in controlling and providing the well distributed and fine microstructure resulting in better tensile strength and elongation.To reduce SDAS,it is commonly known by increasing cooling rate and increasing interface instability by limited-soluble alloy addition.It is,however, unclear that how both cooling rate and limited-soluble alloy,e.g.Sb,relate to each other.This may be the reason that the limited-soluble alloy may not effectively reduce SDAS.To better understand this phenomenon, influences of Sb on solid/liquid interface instability using columnar to equiaxed transition （CET） were studied in the directionally solidification experiment.From macrographs and micrographs,it was observed that at 0.06-0.18 wt pct Sb the CET min,CET max,CET zone and %CET area gradually increased.The increases of CET max and CET zone in samples with 0.06 to 0.18 wt pct Sb addition results from recalesced zone.On the other hand,the variations of CET max and CET zone in samples with 0.24 to 0.30 wt pct Sb results from equiaxed grain formations that prohibit the growth of columnar grain and latent heat from intermetallic phase solidified.
文摘This paper presents a multi-objective production planning model for a factory operating under a multi-product, and multi-period environment using the lexicographic (pre-emptive) procedure. The model objectives are to maximize the profit, minimize the total cost, and maximize the Overall Service Level (OSL) of the customers. The system consists of three potential suppliers that serve the factory to serve three customers/distributors. The performance of the developed model is illustrated using a verification example. Discussion of the results proved the efficacy of the model. Also, the effect of the deviation percentages on the different objectives is discussed.
文摘Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected by the boundaries between layers of different materials or same material but in different states （solid or liquid or gas）. This paper investigates the effects of ultrasound （US） on the surface of the solidified weld which has been subjected to ultrasonic vibrations of 20 kHz frequency during laser welding. Vibrations due to ultrasound normally exert a very high force which is usually hundred or thousand times the gravity. The transverse waves will also cause movement of molten material in the weld. As the surface of the weld beads were of interest and not the mechanical properties and the microstructure, investigation of bead on plate welds were found to be sufficient. High carbon steel plate was held at one end by the ultrasonic horn through which ultrasound was injected. A bead on plate weld using a CO2 laser （1 kW） was then performed along the center of the plate using three different welding speeds namely, 400, 1200 and 2000 mm per minute. The ultrasonic powers selected were 3 W and 6 W respectively for each welding speed as higher acoustical power was causing ejection of molten metal from the pool during welding. 3D surface measurements and analysis were then made on a section of length 20 mm using a Talysurf machine. The results show that the surface of the weld was affected to different extent depending on the positions being considered in the weld. Some regions were similar to the reference weld whereas some specific regions were heavily disrupted with deep valleys followed by high peak/s. This shows that US vibration of weld pools, even at very small acoustical power, is a more complex problem than other similar processes such as casting because of the very small volume of molten metal involved.
文摘To attain an enhanced combination of mechanical properties for low alloyed steel, the current study has been made to fulfill that growing need in the industry. Its results are introduced within this paper. One step Quenching and Partitioning (Q&P) heat treatment has been applied on Niobium-based microalloyed steel alloy with 0.2 %C, in the form of 2 mm thickness sheets. The target of this study is to investigate the viability of applying that significantly recommended, results-wise, heat treatment on the highly well-suited alloy steel samples, to achieve the main target of enhanced properties. A single temperature of 275°C was used as quenching and Partitioning temperature. Four Partitioning periods (30, 200, 500, and 1000 Seconds) were used for soaking at the same temperature. The results were analyzed in the light of microstructural investigation and mechanical testing. All applied cycles did not enhance the strength but moderately improved the ductility and toughness, mainly caused by the slightly high soaking temperature used. Niobium impact of grain refining was apparent through all cycles. The cycle of 500 Seconds Partitioning time obtained optimum values at that particular temperature. The 1000 Seconds Cycle obtained the worst combination of properties. A set of recommendations are set. More research is required at this point, where a lower Partitioning temperature is advised. In the light of the applied combination of parameters, the Partitioning period at such temperature is advised to be between 500 and 1000 Seconds. A high probability that periods closer to 500 than 1000 Seconds will produce better results. More research is needed between those two values of Partitioning time to precisely determine the optimum time at that temperature on that specific alloy.
文摘Form error measurement is a critical exercise in providing measures for the quality control in the precision manufacturing industry.Coordinate measuring machine （CMM） is one of the automated systems used in the accurate and precise dimensional measurements and geometrical form.This paper aims to study the effect of dynamic original unforeseeable errors at different undulations per revolution （UPR） of standard artifact measurement using selected two types of CMM touchtriggering stylus.Stylus-type and stylus-speed parameters were adopted and utilized throughout the course of experiment.The results are analyzed using fast Fourier transformation to obtain foreseeable geometrical errors due to CMM machine structure and stylus scanning speeds.The results of experiment successfully indicate that the number of UPR plays an important role in determining the CMM accuracy level of the roundness measurement result.Some specific error equations for stylus system and machine structure responses have been postulated and analysed to empirically predict the accuracy of PRISMOBridge-CMM-type at National Institute for Standards （NIS） in egypt.
文摘In this study,we attempted to characterise the effects of date-palm fibre(DPF)and a date-palm fibre/sheep wool hybrid in polyester to enhance high-performance and low-cost composite materials that can be used in insulation building systems,automotive parts,and home furniture.The DPF was treated using 5%NaOH solution;and the sheep wool was cleaned with 50℃hot water and detergents.The composite specimens were prepared with different fibre contents(0%,10%,20%,30%(w))using a compression moulding technique.The effect of fibre reinforcement was analysed in terms of the mechanical properties(tensile,flexural,impact,and hardness)and composite density.Additionally,scanning electron microscopy(SEM)was performed on the fibres before and after treatment,and the fractured surfaces of all composite specimens were examined after tensile testing.The results showed that the 20%DPF/sheep wool hybrid reinforced polyester produced the best results.The ultimate tensile strength and modulus were 27 MPa and 3.69GPa,respectively.The ultimate flexural strength and flexural modulus were 35.4 and 2507 MPa,respectively.The impact strength was 39.5 kJ/m^(2)and the hardness was 64 HB.The density decreased to the lowest value of 1.02 g/cm^(3)with the 30%DPF/sheep wool hybrid.The SEM showed good adhesion and interfacial bonding between DPF/sheep wool hybrid fibres and the polyester matrix,particularly at 20%fibre content.
文摘In this research study,Bambusa ssp,the utilized species of bamboo,was rendered into a more versatile construction material in the form of laminates.The laminated specimens were manufactured using simplified processing methods according to the ASTM D3039 and ASTM D143 standards.Polyvinyl acetate was the adhesive used between the 2-ply laminate.The mechanical properties of the specimens were evaluated through tensile,compressive and bending strength tests according to set standards on the Testometric M500-50AT Universal Testing Machine.The tensile strength of laminated bamboo was comparable to that of redwood,spruce,cedar and pine.The ratio of compressive strength of parallel to perpendicularfibers in compressive tests was in a close range to that of poplar,fir and pine.The correlation in compressive strength values between bamboo and wood confirmed the inherent anisotropic nature of both plant materials.
文摘Bamboo in its raw state is difficult to incorporate in complex structures due to its tubular shape. In this research article, a novel approach to connect bamboo was designed and evaluated in order to integrate sustainable material into modern structures. Several bamboo joints for culm connection were designed based on strength and durability under various loading capacity. The conceptual joints were manufactured and subjected to destructive testing on the Universal Testing Machine, Testometric M500-50AT. From the mechanical properties generated, final modifications and refinements were incorporated into the joint design. Self-drilling metal screw joints were found to be the strongest with a maximum resisting force of around 11 kN in compression and 10 kN in tension. Riveted joints were the second strongest joint, while tightening ring joints, the weakest among the three, could only resist a peak load of 747 N in tension. The joints, designed with metal fittings, proved to be more practical for utilization in assembly design.
文摘The study examines the impact of microstructure and polymethyl methacrylate(PMMA)grafting on the degradability of Zn–Mg alloys.The mechanical properties ofa Zn alloy containing 0.68 wt%Mg and extruded at 200◦C are enhanced for degradable load-bearing applications,addressing a crucial need in the field.The materialexhibits a bimodal grain size distribution that is random texture,consisting of secondary phases,grains,and sub-grains.With an elongation to failure of 16%,theyield and ultimate tensile strengths are 325.9 and 414.5 MPa,respectively,and the compressive yield strength is 450.5 MPa.The“grafting-from”method was used to coat a few micrometers thick of PMMA on both bulk and scaffold Zn alloys to mitigate the corrosion rate.The last one is aporous structure,with a porosity of 65.8%,considered as in the first approach of an orthopedic implant.After being immersed for 720 h,the PMMA-grafted bulkalloy’s corrosion rate decreased from 0.43 to 0.25 mm/y.Similarly,the scaffold alloy’s corrosion rate reduced from 1.24 to 0.49 mm/y.These results indicate that themethod employed could be used for future orthopedic applications.
