金属玻璃基复合材料的微结构效应

基于自由体积理论和Ramberg-Osgood模型,并利用ABAQUS软件,建立颗粒随机分布代表性体积单元模型,模拟了Ti_(64.5)Zr_(14.5)V_(18.5)Cu_(2.5)颗粒增韧Ti基金属玻璃基复合材料在单轴拉伸状态下的微结构效应,讨论了颗粒的体积分数、团聚数目、长径比、定位取向和界面对金属玻璃韧性的影响。结果表明:提高颗粒体积分数能显著提高复合材料的塑性,但部分牺牲了复合材料的强度;增大颗粒长径比能够增强复合材料的塑性和屈服强度;使颗粒的取向与荷载方向成90°或0°,不仅增强了复合材料的塑性,而且与其他排布相比也增强了复合材料的强度;减少团聚数目至2个以下,能明显减少金属玻璃基复合材料的塑性和强度的损失,使团聚中颗粒与荷载成90°,却能改善复合材料的塑性和强度;在颗粒增韧金属玻璃基复合材料中加入零厚度界面,能观察到在主剪切带上颗粒和基体在界面处脱粘,得到与实验现象更加吻合的结果。通过上述的研究能够很好地理解复合材料的微结构效应,并有利于材料的设计。     

不同温度和应变率下Wf/BMG的力学性能

本文对纤维体积百分含量(Vf)为60%的钨丝增强Zr41.25Ti13.75Ni10Cu12.5Be22.5大块非晶基体复合材料(Wt/BMG)的力学性能进行了试验研究,测得该材料在77K到473K温度变化范围内的动静态应力应变曲线.发现其流动应力具有明显的正应变率敏感性;随着试验环境温度的升高,材料的弹性模量、屈服应力不断降低,材料的最终塑性应变值则呈升高趋势;Wf/BMG的断裂模式主要为剪切和纵向劈裂及二者的复合,具体形式受钨丝和基体界面的结合强度影响;钨丝的加入限制剪切带的传播,在界面处形成多条剪切带是复合材料塑性提高的主要原因;Wf/BMG的屈服与基体中由于绝热加热降低粘性而形成的剪切带有关,环境温度和非晶基体玻璃转变温度之差则直接影响剪切带的生成,使得Wf/BMG的屈服极限具有一定的温度敏感性.     

数值模拟SiCp/Al复合材料的微观结构对力学性能的影响

本文运用有限元法模拟了SiC颗粒体积分数和颗粒尺寸对SiCp/Al复合材料弹性模量、屈服强度、延伸率的影响。为了建立与真实显微结构相似的复合材料模型,假定任意尺寸的SiC颗粒随机地分布在SiCp/Al复合材料中。计算结果表明:SiC颗粒体积分数对复合材料的力学性能的影响更加显著。随着体积分数的增加,SiCp/Al复合材料的弹性模量和屈服强度逐渐增加;而其延伸率会相应降低。其应力应变曲线由韧性材料的特性向脆性材料的特性逐渐过渡。相反,当平均颗粒尺寸在一定的范围内变化时,颗粒尺寸对其应力-应变曲线的影响并不显著。     

单向纤维增强陶瓷基复合材料单轴拉伸行为

采用细观力学方法对单向纤维增强陶瓷基复合材料的单轴拉伸应力-应变行为进行了研究。采用Budiansky-Hutchinson-Evans（BHE）剪滞模型分析了复合材料出现损伤时的细观应力场,结合临界基体应变能准则、应变能释放率准则以及Curtin统计模型三种单一失效模型分别描述陶瓷基复合材料基体开裂、界面脱粘以及纤维失效三种损伤机制,确定了基体裂纹间隔、界面脱粘长度和纤维失效体积分数。将剪滞模型与3种单一失效模型相结合,对各个损伤阶段的应力-应变曲线进行模拟,建立了准确的复合材料强韧性预测模型,并讨论了界面参数和纤维韦布尔模量对复合材料损伤以及应力-应变曲线的影响。与室温下陶瓷基复合材料单轴拉伸试验数据进行了对比,各个损伤阶段的应力-应变、失效强度及应变与试验数据吻合较好。     

TiNi形状记忆合金低速冲击性能的数值模拟

采用有限元法数值模拟了TiNi形状记忆合金(SMA)的低速冲击性能。考察马氏体相变过程中不同伪弹性模量和弹性应变极限对TiNi合金低速冲击性能的影响。结果表明,随着冲击速度的增加,4种材料的最大接触载荷和位移量都呈线性增加趋势;冲击速度相同时,3种不同伪弹性模量TiNi合金试样的最大接触载荷和位移量近似相等且都低于45#钢,TiNi合金试样产生的最大Von Mises应力和最大塑性应变都低于45#钢;超弹性模量为2.9GPa的TiNi合金产生的最大Von Mises应力和最大塑性应变均最低。TiNi形状记忆合金较低的超弹性模量和较大的弹性应变极限能够减小冲击过程中的最大Von Mises应力,抑制高塑性应变的产生并使塑性变形区域减小,从而提高TiNi合金的抗冲击性能。     

界面弹塑性对原位SiCp/7075Al复合材料弹性模量影响的数值分析

界面把载荷从基体传递到增强体是复合材料弹性变形阶段的重要强化机制。应用ABAQUS有限元软件模拟分析了界面弹塑性对原位SiCp/7075Al复合材料弹性模量的影响规律,结果表明:界面与基体所需的模量比值与颗粒体积分数有关,并不局限于20%~30%;随着界面弹性模量的增大,基体塑性变形量增大,复合材料塑性性能变差;颗粒体积分数大时,界面/基体模量比取满足增强效果的最小值即可;颗粒体积分数越大,界面性能对复合材料的弹性模量的影响越显著,界面弹塑性比基体弹塑性对复合材料弹性模量的影响更明显,并且界面弹塑性会明显地降低颗粒体积分数比较大的复合材料的弹性模量。     

正交铺设陶瓷基复合材料单轴拉伸行为

采用细观力学方法对正交铺设陶瓷基复合材料单轴拉伸应力-应变行为进行了研究。采用剪滞模型分析了复合材料出现损伤时的细观应力场。采用断裂力学方法、 临界基体应变能准则、 应变能释放率准则及Curtin统计模型4种单一失效模型确定了90°铺层横向裂纹间距、 0°铺层基体裂纹间距、 纤维/基体界面脱粘长度和纤维失效体积分数。将剪滞模型与4种单一损伤模型结合, 对各损伤阶段应力-应变曲线进行了模拟, 建立了复合材料强韧性预测模型。与室温下正交铺设陶瓷基复合材料单轴拉伸应力-应变曲线进行了对比, 各个损伤阶段的应力-应变、 失效强度及应变与试验数据吻合较好。分析了90°铺层横向断裂能、 0°铺层纤维/基体界面剪应力、 界面脱粘能、 纤维Weibull模量对复合材料损伤及拉伸应力-应变曲线的影响。      

SiC颗粒增强铝基复合材料冲击拉伸力学性能的试验研究

对ＳｉＣ颗粒增强铝基复合材料在应变速率为１５０～１０００ｓ＾－１范围内的冲击拉伸力学性能进行了试验研究，得到了材料从弹塑变形直至断裂的完整的应力应变曲线，结果表明ＳｉＣ颗粒增强铝基复合材料是一种应变率敏感材料，随着应变速率的提高，材料的屈服应力，破坏应力以及破坏应变均为相应提高，断口分析表明，ＳｉＣｐ／Ａｌ的破坏形式的比较复杂，是一种颗粒的脆性破坏与铝合金基体的韧性破坏共存，强界面与弱界面共存的混     

高体积分数 SiC P / Al复合材料的拉伸、 压缩与弯曲特性

对高体积分数碳化硅颗粒增强铝基(SiC P/ Al)复合材料的拉伸、 压缩和三点弯曲特性进行了实验研究。结果表明 : 高体积分数 SiC P/ Al 复合材料与低体积分数 SiC P/ Al复合材料相比 , 没有明显的线性屈服阶段。进一步的加载2卸载实验表明 , 在外载荷作用下 , 材料宏观上呈现一种类似金属材料的塑性 , 卸载后留有较大的残余应变 , 再次加载时沿上次卸载路线上升 , 而且拉应力导致的残余应变大于压应力。三点弯曲时材料内部产生残余塑性变形的潜力最大 , 切线模量更稳定。宏观断口分析表明 , 金属基体的非均匀分布导致产生局部渐进的微屈服 ,是使材料性能宏观上类似塑性材料的主要原因。制备过程中的残余应力和基体内部的微缺陷是拉应力比压应力产生更大残余应变的主要原因。     

颗粒增强复合材料刚塑性细观损伤本构模型的验证

验证已建立的刚性颗粒增强复合材料刚塑性细观损伤本构理论的合理性和可靠性。将上述本构理论的数值计算结果与SiC颗粒增强的铝基复合材料单轴拉伸实验结果进行比较。结果表明:由此本构模型得到的应力-应变理论曲线与拉伸实验所得的应力-应变曲线基本吻合,从而验证了该本构模型的合理性和可靠性。因此已建立的刚塑性细观损伤本构模型可用于数值计算,在一定程度上可预测颗粒增强复合材料的力学特性。在此基础上对大、小颗粒增强复合材料的延展性、空洞和颗粒体积分数演化规律等作了讨论。      

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically.

Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly.

This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.     

Insight into the Effects of Reinforcement Shape on Achieving Continuous Martensite Transformation in Phase Transforming Matrix Composites

A continuous martensite transformation is indispensable for achieving large linear superelasticity and low modulus in phase transforming metal-based composites. However, determining how to accurately condition the residual martensite in a shape memory alloy matrix though the reinforcement shape to achieve continuous martensite transformation has been a challenge. Here, we take the finite element method to perform a comparative study of the effects of nanoinclusion shape on the interaction and martensite phase transformation in this new composite. Two typical samples are compared: one reinforced by metallic nanowires and the other by nanoparticles. We find that the residual martensite within the shape memory alloy matrix after a pretreatment can be tailored by the reinforcement shape. In particular, our results show that the shape memory alloy matrix can retain enough residual martensite phases to achieve continuous martensite transformation in the subsequent loading when the aspect ratio of nanoreinforcement is larger than 20. In contrast, the composites reinforced with spherical or low aspect ratio reinforcement show a typical nonlinear superelasticity as a result of a low stress transfer-induced discontinuous martensite transformation within the shape memory alloy matrix.     

Interfacial stress distribution between bovine dentine and resin composite in dentine bonding systems

In finite element stress analysis, the principal interfacial stress at a tensile bond strength of 10 MPa during tensile loading was estimated for the resin composite/dentine material including the bonding area with elastic moduli of 0.03, 0.3, 3.0 and 12.0 GPa assumed in this study. Interfacial stress along the resin composite/bonding area interface or bonding area/dentine interface increased with increasing elastic modulus. The interfacial stress distributed non-uniformly and locally at the most sensitive sites, that is, the edge of the resin composite/bonding area interface with the lowest elastic modulus (0.03 GPa) and the edge of bonding area/dentine interfaces with other elastic modulus values (0.3, 3.0 and 12.0 GPa). The maximum value of interfacial stress increased linearly with increasing elastic modulus of bonding area from 0.03 to 12.0 GPa. This study showed that the distribution of interfacial stress was highly non-uniform along the interfaces of the bonded areas in dentinal adhesives.     

Failure behavior of Cu–Ti–Zr-based bulk metallic glass alloys

Microstructure fracture and mechanical properties of Cu-based bulk metallic glass alloys were investigated. Centrifugal casting into copper molds were used to manufacture basic Cu₄₇Ti₃₃Zr₁₁Ni₉, and modified Cu₄₇Ti₃₃Zr₁₁Ni₇Si₁Sn₁ alloys. Although the alloys show an amorphous structure, TEM images revealed the formation of nanoparticles. At room temperature compression tests reveal fracture strength of 2000 MPa, elastic modulus of 127 GPa, and 1.8% fracture strain for the unmodified basic alloy. Whereas the modified alloy exhibits a fracture strength of 2179 MPa, elastic modulus reaches 123 GPa, and 2.4% fracture strain. So, with the addition of 1 at.% Si and Sn, the fracture strength improves by 9% and the fracture strain improves by 25%, but the fracture behavior under compression conditions exhibits a conical shape similar to that produced by tensile testing of ductile alloys. A proposed fracture mechanism explaining the formation of the conical fracture surface was adopted. The formation of homogeneously distributed nano-size (2–5 nm) precipitates changes the mode of fracture of the metallic glass from single to multiple shear plane modes leading to the conical shape fracture surface morphology.     

Making metallic glasses plastic by control of residual stress

Metallic glasses, now that many compositions can be made in bulk, are of interest for structural applications exploiting their yield stress and yield strain, which are exceptionally high for metallic materials. Their applicability is limited by their near-zero tensile ductility resulting from work-softening and shear localization. Even though metallic glasses can show extensive local plasticity, macroscopically they can effectively be brittle, and much current research is directed at improving their general plasticity. In conventional engineering materials as diverse as silicate glasses and metallic alloys, we can improve mechanical properties by the controlled introduction of compressive surface stresses. Here we demonstrate that we can controllably induce such residual stresses in a bulk metallic glass, and that they improve the mechanical performance, in particular the plasticity, but that the mechanisms underlying the improvements are distinct from those operating in conventional materials.     

承受各种循环加载的TiNi形状记忆合金的超弹性变形行为

TiNi形状记忆合金由于其优良的机械性能、抗腐蚀能力和生物适应性得到广泛的使用。超弹性是TiNi形状记忆合金重要的力学性能之一。本文通过实验研究了不同加载速率和不同实验温度下承受完全循环加载以及部分加载卸载的TiNi形状记忆合金超弹性变形行为。分析了循环变形期间马氏体相变应力和弹性模量变化的特性。研究表明在完全循环加载过程中，由于残余应变的存在，马氏体相变应力随循环增加而减小。马氏体相变应力的变化量（即残余应力）与残余应变成线形关系。对于受过循环变形的机械训练的TiNi形状记忆合金，研究了部分加载和卸载情况下其超弹性变形，分析了相变开始与结束的应力特性。     

Effects of particle plasticity characteristics on local interface stress in particle reinforced composite during uniaxial tension

For elastoplastic particle reinforced metal matrix composites, failure may originate from interface debonding between the particles and the matrix, both elastoplastic and matrix fracture near the interface. To calculate the stress and strain distribution in these regions, a single reinforcing particle axisymmetric unit cell model is used in this article. The nodes at the interface of the particle and the matrix are tied. The development of interfacial decohesion is not modelled. Finite element modelling is used, to reveal the effects of particle strain hardening rate, yield stress and elastic modulus on the interfacial traction vector (or stress vector), interface deformation and the stress distribution within the unit cell, when the composite is under uniaxial tension. The results show that the stress distribution and the interface deformation are sensitive to the strain hardening rate and the yield stress of the particle. With increasing particle strain hardening rate and yield stress, the interfacial traction vector and internal stress distribution vary in larger ranges, the maximum interfacial traction vector and the maximum internal stress both increase, while the interface deformation decreases. In contrast, the particle elastic modulus has little effect on the interfacial traction vector, internal stress and interface deformation.     

Pseudo-ductility in intermingled carbon/glass hybrid composites with highly aligned discontinuous fibres

The aim of this research is to manufacture intermingled hybrid composites using aligned discontinuous fibres to achieve pseudo-ductility. Hybrid composites, made with different types of fibres that provide a balanced suite of modulus, strength and ductility, allow avoiding catastrophic failure that is a key limitation of composites. Two different material combinations of high strength carbon/E-glass and high modulus carbon/E-glass were selected. Several highly aligned and well dispersed short fibre hybrid composites with different carbon/glass ratios were manufactured and tested in tension in order to investigate the carbon ratio effect on the stress–strain curve. Good pseudo-ductile responses were obtained from the high modulus carbon/E-glass composites due to the fragmentation of the carbon fibres. The experimental results were also compared with an analytical solution. The intermingled hybrid composite with 0.25 relative carbon ratio gave the maximum pseudo-ductile strain, 1.1%, with a 110 GPa tensile modulus. Moreover, the initial modulus of the intermingled hybrids with 0.4 relative carbon ratio is 134 GPa, 3.5 times higher than that of E-glass/epoxy composites. The stress–strain curve shows a clear “yield point” at 441 MPa and a well dispersed and gradual damage process.     

Evaluation of grain refiners influence on the mechanical properties in a CuAlBe shape memory alloy by ultrasonic and mechanical tensile testing

This work carried out a non-destructive evaluation of grain size influence on the mechanical properties of a CuAlBe shape memory alloy with and without grain refiners. Ultrasonic signal processing, considering only the longitudinal velocity, was used for the non-destructive evaluation. Therefore, the average modulus of elasticity values found for the CuAlBe shape memory alloy was 45.7 GPa and 57.3 GPa with and without grain refiners, respectively. The corresponding values obtained by conventional mechanical tensile testing were equal to 43.2 GPa and 52.6 GPa, respectively. Additionally the mechanical tensile testing verified that the addition of grain refiners increases the stress of the alloy but has a slight effect on the alloy’s ductility. Thus, the modulus of elasticity and consequently the ultrasonic velocity, as well as the stress and strain values of CuAlBe alloy are fully dependent on its grain size. The ultrasonic analysis shows that this alloy is an excellent sound, vibration and mechanical wave absorber, presenting a high attenuation coefficient related to the wave scattering through the grains. In addition, the ultrasonic signal processing method used here confirms its main advantages of fastness and reliability.