高应变率对AM60镁合金力学性能的影响

分别采用静态拉伸试验机和冲击拉伸试验机测定了AM60压铸镁合金在不同应变率下(0.000 1,0.01,300和1 400 S-1)的拉伸力学性能,重点分析了高应变率对合金力学性能的影响,并用扫描电镜(SEM)对拉伸断口进行了分析.结果表明:在应变率很低和很高时,合金的屈服强度、抗拉强度随着应变率的增加变化不大;从静态和动态(高应变率)结果综合比较来看,应变率对强度和断后伸长率有一定的影响,而弹性模量则对应变率不敏感;另外,动态和静态的断裂方式基本相同,都是以准解理断裂为主,局部区域呈沿晶断裂,局部区域存在典型的缩松断裂形貌.     

无机填料对ABS材料FDM试件的力学性能影响

以丙烯腈-丁二烯-苯乙烯(ABS)为基体,以HGB、GF、ZnO、TiO和Al₂O₃为改性填料,制备五种改性ABS复合材料,进而利用熔融沉积成型(FDM)3D技术打印复合材料试件,测定试件的力学性能,并绘制应力应变曲线,然后进行不同改性材料拉伸强度、杨氏模量及断裂伸长率等力学性能分析。结果表明,与纯ABS材料相比,HGB的填充会导致ABS试件杨氏模量增加,但拉伸强度和断裂伸长率降低;GF的填充能够同时增加ABS试件的拉伸强度、杨氏模量及断裂伸长率;ZnO、TiO及Al₂O₃等纳米颗粒的填充均使ABS试件的拉伸强度、杨氏模量和断裂伸长率增强,其中TiO对ABS拉伸强度的增强效果最好,拉伸强度增加高达35.33%。     

TiAl金属间化合物基合金压缩断裂行为

通过对压缩试样的加载-卸载以及加载-卸载-再加载等试验和相应的裂纹观察、断口观察,详细研究TiM金属间化合物基合金压缩断裂行为.研究结果表明:压缩预加载产生的损伤对压缩断裂行为没有影响,然而对后续的拉伸断裂行为则产生影响,一定程度上大大降低其拉伸断裂应力.对全层和双态组织来说,剪切开裂首先产生于顶面或底面,在压缩试验中顶面和底面的切应力是主要的控制因素.最终的断裂是由顶面和底面产生的剪切裂纹扩展到试样中部并相互连接而诱发.对于双态组织(Duplex,DP)和全层组织(Fully lamellar.FL)来说,纵向开裂的形成原因不同.压缩和拉伸性能的巨大差异是由于其断裂机理不同引起,拉伸试验断裂主要是由正应力控制,然而压缩试验中断裂主要是由切应力控制.     

低碳马氏体延迟断裂特性的研究

金属材料在一定的环境(介质、温度等)条件中,在静拉伸应力作用下,取决于时间的断裂过程,称为延迟断裂(或迟后破坏)。延迟断裂又称应力腐蚀断裂、氢脆断裂或静疲劳等。目前这个领域的名称尚未有统一的命名。延迟断裂是一种极为危险的脆性断裂,几乎所有合金在特定的环境中都可能发生延迟断裂,随着工业     

原位自生TiC与TiB增强钛基复合材料的组织和力学性能

通过真空自耗熔炼、锻造、退火等工艺制备得到不同含量原位自生Ti C、Ti B,以及Ti C+Ti B(体积比1∶1)钛基复合材料,研究了其显微组织、室温和高温(300℃)拉伸性能以及室温压缩性能,并分析了室温拉伸时Ti C和Ti B强化作用之间的耦合关系。结果表明:复合材料的基体组织为变形α组织,Ti C呈细小等轴状和略微粗大椭球状,Ti B呈短纤维状;当增强体总体积分数相同时,Ti C+Ti B的强化效果高于Ti C或Ti B的,且随着增强体体积分数的提高而增强,但复合材料的塑性明显下降;复合材料室温拉伸断裂方式主要是增强体的承载断裂,而高温拉伸时的断裂方式包括增强体的承载断裂和部分Ti B短纤维与基体的脱黏;室温拉伸时,Ti C与Ti B的强化作用与细晶强化作用间满足耦合系数1.5的叠加关系。     

DP780冷轧热镀锌钢板点焊接头的高速拉伸性能

利用拉伸试验设备对1.2mm厚DP780冷轧热镀锌钢板点焊接头分别进行了准静态拉伸和高速拉伸试验,分析了点焊接头的高速拉伸特性,并与母材的进行了对比。结果表明:在准静态拉伸和高速拉伸时,点焊接头试样分别在一侧母材和过渡弧处发生断裂;准静态拉伸时的最大拉伸力为9.90kN,随着应变速率的增大,最大拉伸力逐渐增大,在应变速率为500s~(-1)时达到11.50kN;当应变为0.20~0.25时,点焊接头发生断裂失效,而此时仍处于母材的安全有效区间内。     

酸性介质中双相不锈钢与铁素体不锈钢的应力腐蚀研究

采用慢应变速率拉伸试验(SSRT)、扫描电镜(SEM)断口分析以及金相显微组织分析等方法对TP405铁素体不锈钢及2205双相不锈钢在酸性介质中应力腐蚀开裂(PSCC)行为进行了研究.并评定铁素体不锈钢与双相不锈钢在酸性介质中应力腐蚀开裂的敏感性.为在酸性介质中选择容器用钢提供依据.结果表明,拉伸试样全部断裂在焊缝或热影响区.试样断口形貌呈准解理断裂和韧性断裂.2205双相不锈钢的应力腐蚀敏感性比TP405铁素体不锈钢低.     

断裂韧性评估的两模型比较

基于EWF方法,通过将两种材料拉伸试样比断裂总功的计算结果与拉伸测试所得结果进行对比,对目前存在的两种(三区和二区模型)用于描述断裂韧带塑性变形的理论模型进行比较。最终得出三区模型具有较高的精度更为合理的结论。     

碳纤维/玻璃纤维/石墨协同改性PTFE复合材料力学性能

通过机械混合、冷压和烧结成型制备了碳纤维、玻璃纤维和石墨填充协同改性聚四氟乙烯(PTFE)复合材料。对比分析了不同样品的拉伸、冲击和压缩等力学性能。结果表明:玻纤和碳纤维使复合材料冲击强度下降;玻纤使复合材料拉伸强度下降,碳纤维则使复合材料拉伸强度稍有增强;玻纤和碳纤维均使复合材料压缩强度增加,但碳纤维的增强效果更为明显;石墨、玻纤和碳纤维协同增强PTFE复合材料的拉伸强度较高,弹性模量较大,断裂伸长率较高,抗压缩性能明显提高,且材料拉伸时呈塑性断裂,是综合力学性能较好的高性能润滑密封材料。     

切口强度与断裂韧性

本文根据切口应变分析和正应变断裂准则,导出了切口根部裂纹准则、切口强度和韧性以及断裂韧性的表达式。用本文给出的公式干口延性金属的拉伸性能,以及微观结构参数,估算的裂纹起始 COD、切口强度、切口断裂劬性 K_(IA)和断裂切性 K_(IC)之值,均与实验结果符合良好。     

High-temperature tensile behavior of diffusion-welded hastelloy X

Changes in the material properties of alloys subjected to diffusion welding need to be analyzed to increase the adoption of compact heat exchangers in American Society of Mechanical Engineers standards. Hastelloy X was diffusion-welded in this study following a procedure recently developed by the authors. A metallographic study showed that the interface was discernible with some grains migrated across the interface. Satisfactory tensile properties were obtained at 25 °C, but the tensile samples were fractured at/near the interface with ∼40 % of tensile elongation in the tensile tests. The minimum strength reduction factors of the yield strength and tensile strength were 0.799 and 0.843, respectively. Dimples were extensively observed on the fracture surfaces, but the fracture surfaces were predominantly flat owing to the remnant Mo-rich M₆C carbides (stringers).

     

ZrO2-Y2O3陶瓷双相（t＋m）组织的复合韧化

本文采用TEM及XRD等手段研究了ZrO2-2mol%Y2O3陶瓷的组织结构并测试了力学性能。结果表明：随烧结温度升高,致密度增加,但硬度却随单斜相含量的增多而下降。与单一的四方相（TZP）相比,含有显微裂纹的t＋m（PSZ）双相组织具有更高的断裂韧度。这是由于前者只有相变韧化效果,而后者则同时有相变韧化、显微裂纹韧化及残余应力（应变）韧化的多重复合机理作用的结果。     

Effect of copper content on the mechanical and sliding wear properties of monotectoid-based zinc-aluminium-copper alloys

One binary zinc-aluminium monotectoid and five ternary zinc-aluminium-copper alloys were produced by permanent mould casting. Their wear properties were examined using a block-on-ring test machine. Hardness, tensile strength and percentage elongation of the alloys were also determined and microhardness of aluminium-rich α phase was measured.It was observed that the hardness of the alloys increased continuously with increasing copper content up to 5%. Their tensile strength also increased with increasing copper content up to 2%, but above this level the strength decreased as the copper content increased further. Microhardness of the aluminium-rich α phase was also affected by the copper content in a manner similar to that of the tensile strength. It was found that the wear loss of the alloys decreased with increasing copper content and reached a minimum at 2% Cu for a sliding distance of 700 km. However, the coefficient of friction and temperature due to frictional heating were found to be generally less for the copper containing alloys than the one without the element. The effect of copper on the wear behaviour of the alloys was explained in terms of their microstructure, hardness, tensile strength, percentage elongation and microhardness of the α phase.     

Sc和Zr对Al-Mg铸造合金组织和力学性能的影响

采用金相显微镜、扫描电镜和能谱分析,研究Sc、Zr对Al-Mg铸造合金组织和力学性能的影响。结果表明,添加0．2％～0．4％的Sc,会使合金铸态组织中的部分树枝晶变为等轴晶,且Sc含量越高,合金铸态组织越细;随着Sc含量的增加,合金的抗拉强度升高,Sc含量为0．4％的合金抗拉强度提高30％。添加0．1％～0．2％的Zr也会使合金铸态组织中的部分树枝晶变为等轴晶,但是效果不如Sc;随着Zr含量的增加,合金的延伸率升高,Zr含量为0．2％的合金延伸率高达11．9％。     

基本参数X射线荧光光谱法分析贵金属合金样品

基本参数法具有校准元素间的相互影响的功能,同时由于在其浓度归一化的过程中能够消去测量面积和探测立体角项,因此具有校正样品测量面积和形状影响的能力,十分适于贵金属合金及其饰物的分析。本文报道用R Ⅸ 2100型X射线荧光光谱仪分析贵金属合金及其饰物样品的方法。实验表明,通过选择适当的测量谱线和背景测量角度,并将邻近谱线对测量谱线背景的影响作为谱线重叠处理,可以确保分析的准确度。同一样品不同测量面积下得到的分析值的一致性良好;形状与标准样相差很大的实际样品的分析结果也令人满意。用不同样品各进行8次重复分析得到的各元素的分析精密度(RSD％)分别为:Au(96.99％)=0.02,Au(75.00％)=0.04;Ag(1.02％)=1.48,Ag(8.96％)=0.35;Cu(1.00％)=0.83,Cu(15.97％)=0.15;Zn(1.01％)=0.70;Pt(80.00％)=0.03;Pd(19.92％)=0.17;Ni(99.99％)=0.004。     

The structure and mechanical properties of amorphous and nanocrystalline Fe–Si–B alloys

This article describes the results of investigations of the microstructure of failure surfaces and the mechanism of deformation of an amorphous Fe₈₀Si₁₁B₉ alloy, nanocrystallized with the use of Nd:YAG pulsed laser heating. The research included ‘in situ’ tensile testing in a scanning electron microscope. Mechanical properties were also measured on an Instron‐type machine for the amorphous and nanocrystalline alloys. The mechanical tensile tests performed on the amorphous and nanocrystalline samples showed a ductile fracture surface with very high fracture stress. Detailed observations of the flow deformation and fractures revealed the relationship between the quenched‐in crystalline and mechanical behaviour.     

全层状TiAl基合金拉伸试验断裂过程及机理

通过对全层组织TiAl基合金不同缺口试样进行原位拉伸试验,结合数据分析以及断口形貌的观察,研究TiAl基合金拉伸的断裂过程和断裂机理.研究发现在原位拉伸试验中,对于直缺口试样,裂纹起裂于缺口根部,其断裂过程主要是主裂纹(沿层裂纹)首先起裂、扩展、连接,然后形成解理断裂起裂源.这一起裂源形成的同时,在刚好能满足Griffiths脆性解理断裂所需要的临界裂纹尺寸时,引起整个试件发生脆性解理断裂.裂纹首先起裂于层间,层间是薄弱环节,断裂方式是穿层断裂和沿层断裂的混合体,以穿层断裂为主.对于大圆弧和平板试样,这种材料的断裂过程是:首先在较高外加载荷下,在标距范围内比较薄弱的区域沿层开裂,随着外加载荷的进一步增加,这些微裂纹扩展,当微裂纹引起的应力集中和外加载荷共同作用足以引起微裂纹进一步贯穿的瞬间,即能量积累到一定程度时,试样整体发生解理断裂.很多试样的断裂是直接起裂的过程,一旦产生裂纹试样立即解理断裂,即这种材料的强度较高,材料很难产生裂纹,也不易损伤.     

硼含量对铅镁铝合金组织与力学性能的影响

采用真空熔炼法制备了含硼的铅镁铝合金,通过扫描电子显微镜、X射线衍射仪、能谱仪和力学性能试验机等研究了硼含量对合金组织与力学性能的影响。结果表明:添加硼后,合金中出现了黑色的颗粒状AlB2相,且与Mg-Mg17Al12共晶组织相伴生;随着硼含量的增加,AlB2相分布趋于均匀化,Mg-Mg17Al12共晶相增多;当硼的质量分数为1%时,合金的力学性能最好,抗拉强度、硬度和伸长率分别为105MPa,160MPa和6.87%,室温拉伸断口主要为韧性断裂和准解理断裂的混合特征。     

A viscoelastic analysis of the tensile weakening of deep femoral head articular cartilage

Articular cartilage from below the surface of the femoral head of the hip joint shows a profound age-dependent weakening in its tensile mechanical properties. This ageing is also associated with a reduced viscoelastic response in the older tissue. A constitutive model of the viscoelastic behaviour of deep articular cartilage (as discussed by Egan in 1988) is used to generate a graphical pattern which represents the mechanical behaviour. This constitutive approach suggests that the tensile weakening of the older cartilage is due to an age-related reduction in the recruitment of load-carrying structures as the tissue is deformed. The viscoelastic constitutive model also predicts a reduction in the tensile strength of deep articular cartilage with rate of deformation. This prediction is supported by experimental fracture stress data. A weakening of the tensile integrity of the microstructure of articular cartilage could make the tissue less able to sustain normal compressive physiological loading without damage and thus make the tissue more susceptible to osteoarthritic degeneration. The constitutive approach indicates that the weakening of the older tissue may be related to changes within the microstructure which determine how applied mechanical energy is stored and dissipated.     

Effects of Silicon Content on the Mechanical Properties and Lubricated Wear Behaviour of Al–40Zn–3Cu–(0–5)Si Alloys

In this work, one ternary Al–40Zn–3Cu and seven quaternary Al–40Zn–3Cu–(0.25–5)Si alloys were synthesized by permanent mould casting. Their microstructure, mechanical and lubricated wear properties were investigated using appropriate test apparatus and techniques. As the silicon content increased the hardness of the alloys increased, but their elongation to fracture decreased. Tensile strength of the alloys decreased with increasing silicon content following a sharp decrease and a slight increase. Among the silicon-containing quaternary alloys the highest and the lowest tensile strength values (348 and 305 MPa) were obtained with the Al–40Zn–3Cu–2Si and Al–40Zn–3Cu–5Si alloys, respectively, while the base alloy (Al–40Zn–3Cu) exhibited a tensile strength of 390 MPa. However, the volume loss due to wear of the alloys increased with increasing silicon content after showing an initial increase and a sharp decrease. The lowest wear loss was obtained with the alloy containing approximately 2% Si which has the highest tensile strength among the quaternary alloys containing more than 0.25% Si. Wear surfaces of the alloys were characterized mainly by smearing indicating that adhesion is the dominant wear mechanism for the experimental alloys.