Enhancing mechanical properties and avoiding cracks by simulation of quenching connecting rods

If the service load onto a part is heavy, e.g. for the connecting rods of high-power diesel engine, high mechanical properties are critically required. When quenched in oil, it cannot meet the requirements. While quenching it in aqueous polymer quenchant or water, the mechanical properties could be higher than that required but cracking would occasionally happen. In order to obtain the expected mechanical properties and avoid cracking by quenching and tempering, the heat transfer coefficients of quenchants were measured and calculated, and the quenching process of connecting rods was simulated by using finite element method so that its processing parameters were determined. The results show that the mechanical properties of the treated rods have been enhanced and cracks were avoided.     

Influence of the concentration of carbon nanotubes on electrical conductivity of magnetically aligned MWCNT–polypyrrole composites

The goal of this work is to study the effect of high magnetic pulses on electrical property of carbon nanotube–polypyrrole (CNT–PPy) composites with different CNT concentrations. CNT–PPy composites are produced in fractions of 1, 5 and 9 wt%. During the polymerization process, the CNTs are homogeneously dispersed throughout the polymer matrix in an ultrasonic bath. Nanocomposite rods are prepared. After exposure to 30 magnetic pulses, the resistivity of the rods is measured. The surface conductivity of thin tablets of composites is studied by 4-probe technique. The magnitude of the pulsed magnetic field is 10 Tesla with time duration of 1.5 ms. The results show that after applying 30 magnetic pulses, the electrical resistivity of the composites decreases depending on the concentration of CNTs in the composites. The orientation of CNTs is probed by atomic force microscopy (AFM) technique. AFM images approved alignment of CNT–polymer fibres in the magnetic field. We found that the enhancement in the electrical properties of CNT–PPy composites is due to rearrangement and alignment of CNTs in a high magnetic field. The stability of nano-composites is studied by Fourier transform infrared spectroscopy.     

Microstructure and Compression Strength of Novel TRIP‐Steel/Mg‐PSZ Composites

Novel composites on basis of austenitic stainless TRIP‐steel as matrix with reinforcements of Mg‐PSZ are presented. Compact rods were produced by cold isostatic pressing and sintering, square honeycomb samples by the ceramic extrusion technique. The samples are characterized by optical and scanning electron microscopy before and after deformation, showing the microstructure and the deformation‐ induced martensite formation. The mechanical properties of samples with 5 vol% zirconia are superior compared to zirconia‐free samples and composites with higher zirconia contents in terms of bending and compression tests. The honeycomb samples exhibit extraordinary high specific energy absorption in compression.     

Moisture absorption of unidirectional hybrid composites

Unidirectional hybrid composite rods were conditioned in humid air to investigate the sorption kinetics and the effects of moisture on mechanical and physical properties. Sorption curves were obtained for both hybrid and non-hybrid composite rods to determine characteristic parameters, including the diffusion coefficient (D) and the maximum moisture uptake (M_∞). The moisture uptake for the hybrid composites generally exhibited Fickian behavior (no hybridization effects), behaving much like non-hybrid composites. A two-dimensional diffusion model was employed to calculate moisture diffusivities in the longitudinal direction. Interfaces and thermally-induced residual stresses affected the moisture diffusion. In addition, the effect of hygrothermal aging on glass transition temperature (T_g), short beam shear strength (SBS), and tensile strength was determined for hygrothermal exposure at 60 °C and 85% relative humidity (RH). Property retention and reversibility of property degradation were also measured. Microscopic inspection revealed no evidence of damage.     

Influence of testing method on mechanical properties of ceramic matrix composites

Mechanical properties of a monolithic zircon and zircon-matrix composites reinforced with silicon carbide monofilaments and/or whiskers were measured in three-point flexure and uniaxial tension modes to study the influence of testing methods on mechanical behaviour. A number of composite characteristics, such as the first-matrix cracking stress and strain, the ultimate composite strength and strain, and the modulus were obtained from the load-deflection behaviour in flexure and tension tests. The results indicated that the modulus values and the qualitative dependence of mechanical properties on composite parameters were similar in flexure and tension tests. In contrast, all of the other mechanical properties of the monolithic and composites were different in tests performed in flexure and tension modes. Typically, the first-matrix cracking stress and strain were higher in flexure tests than in tension tests, and these stress and strain values were independent of the filament-matrix interfacial properties. Similarly, the ultimate strengths of the monolithic and composites were higher in flexure than in tension, and these strengths were independent of interfacial properties. Therefore, the mechanical properties of composites obtained in flexure should not be used for a quantitative comparison with the predictions of micromechanical models, which are derived under the assumption of a uniform tensile stress. However, the flexure data are perfectly valid in demonstrating the qualitative dependence of mechanical properties on composite parameters.     

Characterization and biodegradability of polypropylene composites using agricultural residues and waste fish

The objective of this research was to study the potential of waste agricultural residues such as rice-husk fiber (RHF), bagasse fiber (BF), and waste fish (WF) as reinforcing and biodegradable agents for thermoplastic composites. Addition of maleic anhydride grafted polypropylene (MAPP) as coupling agent was performed to promote polymer/fiber interfacial adhesion. Several composites with various polypropylene (PP) as polymer matrix, RHF, BF, WF, and MAPP contents were fabricated by melt compounding in a twin-screw extruder and then by injection molding. The resulting composites were evaluated through mechanical properties in terms of tensile, flexural, elongation at break and Izod notched impact following ASTM procedures. Biodegradability of the composites was measured using soil burial test in order to study the rates of biodegradation of the composites. In general, the addition of RHF and BF promoted an increase in the mechanical properties, except impact strength, compared with the neat PP. According to the results, WF did not have reinforcing effect on the mechanical properties, while it could considerably improve the biodegradation of the composites. It was found that the composites with high content of WF had higher degradation rate. Except impact strength, all mechanical properties were found to enhance with increase in cellulosic fiber loading In addition, mechanical properties and biodegradability of the composites made up using RHF was superior to those of the composites fabricated with BF, due to its morphological (aspect ratio) characteristics.     

Compressive and Tensile Behaviours of PLLA Matrix Composites Reinforced with Randomly Dispersed Flax Fibres

Nowadays, the ecological footprint of a material is becoming tremendously important. The Poly l-Lactide Acid (PLLA) matrix composites reinforced by randomly scattered flax fibres have mechanical properties similar to polyester/glass composites [1], lower environmental impacts and can be compost at the end of their lives. In this study, the mechanical characterization of biocomposites has been pushed further with the determination of the compressive and tensile properties. Furthermore, the mechanical properties of single flax fibres have been measured and implemented in a micro-mechanical estimation of the composite elastic modulus. Tensile and compressive stiffness determined by the mechanical analyses show very good correlations with the mathematical estimation.     

Cytocompatibility,degradation, mechanical property retention and ion release profiles for phosphate glass fibre reinforced composite rods

Fibre reinforced composites have recently received much attention as potential bone fracture fixation applications. Bioresorbable composites based on poly lactic acid (PLA) and phosphate based glass fibre were investigated according to ion release, degradation, biocompatibility and mechanical retention profiles. The phosphate based glass fibres used in this study had the composition of 40P₂O₅–24MgO–16CaO–16Na₂O–4Fe₂O₃ in mol% (P40). The degradation and ion release profiles for the composites showed similar trends with the amount of sodium and orthophosphate ions released being greater than the other cations and anions investigated. This was attributed to low Dietzal's field strength for the Na⁺ in comparison with Mg^2 + and Ca^2 + and breakdown of longer chain polyphosphates into orthophosphate ions. P40 composites exhibited good biocompatibility to human mesenchymal stem cells (MSCs), which was suggested to be due to the low degradation rate of P40 fibres. After 63 days immersion in PBS at 37 °C, the P40 composite rods lost ~ 1.1% of mass. The wet flexural, shear and compressive strengths for P40 UD rods were ~ 70%, ~ 80% and ~ 50% of their initial dry values after 3 days of degradation, whereas the flexural modulus, shear and compressive strengths were ~ 70%, ~ 80%, and ~ 65% respectively. Subsequently, the mechanical properties remained stable for the duration of the study at 63 days. The initial decrease in mechanical properties was attributed to a combination of the plasticisation effect of water and degradation of the fibre–matrix interface, with the subsequent linear behaviour being attributed to the chemical durability of P40 fibres. P40 composite rods showed low degradation and ion release rates, good biocompatibility and maintained mechanical properties similar to cortical bone for the duration of the study. Therefore, P40 composite rods have huge potential as resorbable intramedullary nails or rods.     

Thermal stability and flammability of coconut fiber reinforced poly(lactic acid) composites

This study examined the mechanical and thermophysical behavior of green composites. In the preparation procedure of the composite, a plasma treatment was applied to the surface of the coconut fibers to improve the interfacial adhesion between the fibers and matrix. The coconut fiber-reinforced PLA composites were prepared using the commingled yarn method. The mechanical properties of the composites, such as tensile strength, Young’s modulus, and elongation at break were examined, and the shrinkage and flame retardant properties of the specimens were measured. From these experiments, the effect of the plasma treatment on the mechanical and thermophysical behavior of the coconut fibers/PLA composites was identified. In addition, morphological analysis was performed using scanning electron microscopy.     

AZ31镁合金棒材循环扭转变形及其对力学性能的影响

在室温条件下,对AZ31镁合金挤压棒材进行循环扭转变形,测试了扭转变形过程的力学性能以及变形后的微观组织和织构特征,并对扭转变形对镁合金棒材的力学性能影响进行了分析。结果表明:镁合金棒材在循环扭转过程中得到了严格对称的应力-应变滞回线,并且随着循环周期的增加,由于加工硬化和内部微裂纹扩展的共同影响,应力-应变滞回线上的应力峰值呈现先增加后减小的特征。在最大扭转角分别为60°和90°条件下,应力峰值出现在第四周期。镁合金棒材扭转变形后的晶粒中出现大量的拉伸孪晶带,孪晶启动使晶粒的 C 轴转向棒材轴线方向。镁合金棒材扭转变形后的力学性能测试结果显示,循环扭转变形明显提高了镁合金棒材压缩变形的屈服强度,其值由扭转前的约100MPa最大提高至约200MPa。     

The effect of interfacial adhesion and morphology on the mechanical properties of polypropylene composites containing different acid surface treated sepiolites

The study of the microstructure of polymeric composites and its relationship to mechanical properties, are of great importance. In the present study vv8 have carried out a study of the microstructure of polymeric composites of polypropylene and different sepiolites treated with organic acids, in order to determine the mesophase produced around We filler particles and its relationship with the mechanical properties of the composites. This study was made using scanning electron microscopy, differential Scanning calorimetry and mechanical tests.     

碳纳米管增强镁基复合材料导热性能研究

镁及其合金是目前最轻的金属结构材料,合金化虽然提升了镁合金的力学性能,但导致其导热性能严重下降,限制了镁合金的应用。碳纳米管(CNTs)因具有优异的力学、热学等性能,是最理想的增强体之一,可以用于改善镁合金的力学性能和热学性能。采用粉末冶金法分别以纯Mg、Mg-9Al合金、Mg-6Zn合金为基体制备了不同CNTs含量的镁基复合材料,利用光学显微镜、扫描电子显微镜、透射电子显微镜对复合材料微观组织、基体与增强体界面及析出相进行表征,并对复合材料的拉伸性能和热学性能进行测试。研究结果表明,当CNTs质量分数不超过1.0%时,可提高纯镁基复合材料的导热性能,力学性能仅有稍微降低;将CNTs添加到Mg-9Al合金中,可以促进纳米尺度β-Mg 17 Al 12相在CNTs周围析出,降低了Al在Mg基体中的固溶度,使CNTs/Mg-9Al复合材料的导热性能有所提高。此外,在CNTs/Mg-6Zn复合材料界面处存在C原子和Mg原子的相互嵌入区,这种嵌入型界面不仅有利于复合材料力学性能的提高,也使CNTs起到加速电子移动的“桥”的作用,有利于该复合材料热导率的提高。当CNTs质量分数为0.6%时,CNTs/Mg-6Zn复合材料具有较为优异的热学性能和力学性能,其热导率为127.0 W/(m·K),抗拉强度为303.0 MPa,屈服强度为204.0 MPa,伸长率为5.0%。     

碳毡及编织结构碳/碳复合材料常温力学性能研究

为研究两种不同预制体增强的碳/碳(C/C)复合材料的损伤破坏机制差别,将为该材料应用于结构件提供依据,对碳毡及2.5D编织结构增强的C/C复合材料的常温弯曲、剪切、压缩性能进行了测试,并用扫描电镜观察其断面形貌,对C/C复合材料在静态载荷下的力学性能及损伤破坏行为进行研究,探讨有关因素对材料性能和损伤破坏的影响.研究结果表明:两种不同增强体的C/C复合材料的断裂机理存在很大差异,且密度对C/C复合材料的常温力学性能有较大的影响.     

Aluminium nitride–molybdenum ceramic matrix composites: influence of molybdenum concentration on the mechanical properties

Aluminium nitride–molybdenum ceramic matrix composites are produced by hotpressing a mixture of two powders. Mechanical properties of a series of samples are measured in order to study the effect of molybdenum phase on the behaviour of composite. Three-point bend strength increases from a value of 270 MPa for pure aluminium nitride to 571 MPa for a composite containing 40% by volume of metallic phase. Fracture toughness measured by the single-edged precracked beam (SEPB) technique, is also increased as a function of molybdenum concentration. From 2.3 MPam^1/2 for pure AlN we obtain a value of 6.9 MPam^1/2 in the case of composite containing 40% by volume of metallic phase. This very important increase in the mechanical properties of AIN-Mo composites is attributed to higher mechanical properties of molybdenum and an adherent interface between AIN and Mo grains. This revised version was published online in November 2006 with corrections to the Cover Date.     

PVDF对芳纶无纺布/环氧树脂共固化复合材料力学和阻尼性能的影响

为评价热塑性结晶聚合物聚偏二氟乙烯(PVDF)对共固化复合材料动态力学和阻尼性能的影响,首先,将PVDF负载到芳纶无纺布(ANF)上,采用共固化工艺制备了PVDF-ANF/环氧树脂(EP)结构阻尼复合材料。然后,利用动态机械分析仪测试了PVDF-ANF/EP复合材料的损耗因子、损耗模量和储能模量的温度谱;通过弯曲强度、弯曲模量和层间剪切强度的测试评价了复合材料的静态力学性能;通过单悬臂梁振动实验测试了复合材料的共振频率及自由振动衰减曲线,并计算了损耗因子;通过I型、II型层间断裂韧性实验及断面微观形貌的观察研究了复合材料的断裂韧性及增韧机制。最后,对复合材料的微观结构进行分析,探讨了其兼具力学性能和阻尼性能的结构内因。结果表明:通过在ANF表面负载PVDF,可在不引起复合材料力学性能明显下降的前提下,进一步提高PVDF-ANF/EP复合材料的阻尼性能和层间断裂韧性,复合材料的损耗因子提高了33.3%,I型和II型断裂韧性分别提高了168%和208%。     

Micromechanics models for mechanical and thermomechanical properties of 3D through-the-thickness angle interlock woven composites

In this paper, a laminate block modeling approach for three-dimensional (3D) through-the-thickness angle interlock woven composites is used to develop one finite element analysis (FEA) model and two analytical models, namely the “ZXY model” and the “ZYX model”. These models can be used to determine the mechanical properties and the coefficients of thermal expansion for 3D through-the-thickness angle interlock woven composites. A parametric study shows that there is good agreement between these FEA and analytical models. The parametric study also demonstrates the effects of the fiber volume fraction of the warp weaver (i.e., z yarn) and the space between two adjacent filler yarns on the mechanical properties and the coefficients of thermal expansion. Finally, the present models are found to correlate reasonably well with the predicted and measured results available in the literature.     

AZ80 and ZC71/SiC/12p closed die forgings for automotive applications: technical and economic assessment of possible mass production

Abstract

In this study, redesigning for equal functional properties and rapid prototyping of hot forged automotive parts based on commercially available wrought magnesium alloys (AZ80) and composites (AZ80/SiC/12p) were performed. To achieve the same functional properties in a forged automotive component irrespective of the structural material selected, an automotive connecting rod, mass produced in aluminium alloy 6061, was redesigned to use wrought magnesium alloy (AZ80A) and particle reinforced magnesium alloy matrix composite (ZC71/SiC/12p). By applying conventional hot forging technology, prototype connecting rods were forged, trimmed, and heat-treated on a semiindustrial scale. The microstructure of both as extruded and hot forged specimens was examined and the tensile properties of AZ80, ZC71/SiC/12p, 6061 and 6061/SiC/15p test bars machined from hot forged connecting rods were measured. Weight reduction in the redesigned connecting rods was determined and the substitution of magnesium and aluminium based materials for steel was compared in terms of cost.     

Effect of reinforcing layer on shape fixity and time-dependent deployment in shape-memory polymer textile composites

The purpose of the present study is to model shape fixity and time-dependent deployment in shape-memory polymer composites (SMPCs) and to evaluate the effect of textiles’ tensile and bending moduli on these properties. We constructed an SMPC model by combining SMP layers and a reinforcing layer. We also considered the thermo-viscoelasticity of SMP and the difference in values between the tensile and bending moduli of the reinforcing layer. Employing this model, we simulated deployment under pure bending conditions. Comparison with experimental results confirmed that our proposed model is able to simulate shape fixity and time-dependent deployment in SMPCs. We also confirmed that the bending modulus is an important factor for shape fixity and time-dependent deployment, whereas the tensile modulus has nothing to do with these properties.     

Influence of cooling condition on properties of extruded aluminum alloy matrix composites

This paper discusses the influence of applying water cooling after extrusion on the stability of mechanical properties on the AA6061-7.5 vol. % SiC composite rods cross section. The materials were prepared via powder metallurgy processing using extrusion with a reversibly rotating die at the last technological stage. The mechanical properties, texture and microstructure of composites were analyzed following the experiment. In both deformed samples the XRD measurements indicated that the <111> was the predominant orientation, which, however, was weaker towards the edge of the specimen. Moreover, some differences in microhardness between the center and the edge of water cooled rod were observed.     

Improvement of wear resistance behaviour of laser metal deposited Ti6Al4V/Mo composites

Titanium and its alloys are materials found to exhibit wonderful properties such as its lightweight and, excellent mechanical properties – tensile strength and toughness even at elevated temperatures, extraordinary corrosion resistance behaviour and ability to withstand high temperatures. These unique properties have made Ti6Al4V attractive for a range of industrial applications. Some of the successful applications include medical implants and prosthesis, connecting rods for automotive, aerospace, oil and gas, sports equipment, gas turbine engines and space crafts. However, the high cost and poor wear resistance of Ti6Al4V limits its use for specific applications. This study investigates the wear resistance of the laser deposited Ti6Al4V composite and its enhancement with molybdenum. In this study, the Ti6Al4V/Mo composites were produced, the effect of influencing process parameter was investigated, and the produced Ti6Al4V‐Mo composites were further examined through various tests. The results revealed that the Ti6Al4V/Mo composite produced at varying laser powers had improved wear resistant when compared to the Ti6Al4V substrate. A direct correlation between the wear resistance and hardness was also observed.