直剪仪多级液压加载系统的设计与控制

岩石材料不同形状接触面的静动力学特性是岩石力学研究重点。接触面力学特性研究的一个基本途径是通过接触面基本力学特性试验。为了得到稳定的岩体结构面抗剪强度,需要对不同尺寸的岩体结构面试样进行抗剪强度直剪试验。以现有直剪仪为基础,提出新设备的液压系统和控制方案,并对直剪仪法向力和剪切力的控制精度和方法等问题进行了分析。试验测试表明:该试验仪的测试结果可信,精度能满足工程设计要求。文中的研究为岩石试验提供了大压力范围、柔性控制的仪器设备,为测试试样的剪胀和尺寸效应提供装备。     

试样厚度对微冲剪试验结果的影响

采用微冲剪试验方法,根据其测试原理对不同厚度的TC4钛合金试样进行研究,确定了试样的厚度对于试验结果存在影响;同时对微冲剪试验测定金属材料性能的方法、试样制备以及结果分析等方面都作了研究和分析;并通过微冲剪试验和常规拉伸试验得到了抗剪强度和抗拉强度的经验关系式.     

机场压实填土抗剪强度的试验研究

采用原位直剪试验、室内中型直剪试验等测试手段,运用优定斜率法等数理统计方法,对机场高填方压实土的强度特性进行了分类研究,为场区设计方案的优化、稳定性评价与治理,提供了参数。该试验成果可供类似工程借鉴、参考。     

时效对BGA无铅焊点抗剪强度和断裂模式的影响

测试了BGA(球栅阵列)板级封装Sn-3.0Ag-0.5Cu焊点经时效后的抗剪强度,并采用三维超景深显微镜对全部试样焊点的断裂模式进行统计分析。对比研究不同时效温度、时效时间和焊盘处理方式(OSP,Ni/Pd/Au)对焊点抗剪强度及断裂模式的影响。试验结果表明:时效温度越高,时间越长,焊点的抗剪强度越低,在相同时效条件下,焊盘经Ni/Pd/Au处理的焊点抗剪强度高于经OSP处理的焊点抗剪强度;断裂模式随时效温度的升高和时间的延长,由焊球断裂向界面开裂及焊盘失效转变。     

灰铸铁抗拉强度与抗剪强度的关系

对灰铸铁的抗拉强度和抗剪强度进行测量，将试验数据进行拟合回归得出抗拉强度与抗剪强度的关系曲线。找出了单铸试棒和本体试棒抗拉强度及抗剪强度之间的差别.     

BGA封装器件焊点抗剪强度的试验

采用微焊点强度测试仪研究了Sn-Pb共晶钎料BGA（球栅阵列封装技术）封装器件焊点的抗剪强度，并对不同直径的BGA球焊点的抗剪强度进行了比较。研究结果表明，在相同条件下，BGA球直径越大，抗剪强度越小，共晶钎料BGA球焊点的抗剪强度比锡铅合金钎糕点自身的抗剪强度大。     

Ge对SnAgCu/Cu钎焊接头抗剪强度与断口的影响

在化学元素周期表中Ge元素与Sn元素相邻,同为第Ⅳ主族元素,物理与化学性能有许多近似。文中在无铅钎料Sn2．5Ag0．7Cu中添加少量Ge元素（0．25,0．5,0．75,1．0,质量分数,％）,设计、焊接了剪切试样,测试了接头抗剪强度,并且对断口做了扫描电镜和能谱分析。结果表明,添加少量Ge元素以后,接头的抗剪强度有显著提高;接头的断裂形式主要是韧性断裂,并且大都有二次裂纹;添加Ge元素后在剪切断口表面形成很多韧窝;金属间化合物Cu6Sn5对韧窝的形成有一定的作用。     

时效对SnCuSb/Cu钎焊接头抗剪强度与断口特征的影响

研究了150℃时效对Sn-0.7Cu-xSb/Cu(x=0,0.25,0.5,0.75,1.0)钎焊接头抗剪强度和断口特征的影响.结果表明,随着Sb元素含量的增加,钎焊接头的抗剪强度升高;接头抗剪强度随时效时间的增加而明显降低.接头剪切断裂的位置是在钎料上,也出现在钎料和金属间化合物Cu6Sn5之间.对于焊后态试样,其断裂位置在钎料上的情况占绝大部分,断口上分布有大量韧窝,断裂类型主要是韧性断裂.随时效时间的增加,接头的断裂位置向钎料与界面化合物各占一半过渡.时效500h,断口处已经可以看到Cu3Sn的存在,断口已经由韧性转变为脆性.     

加载速率对SnAgCu钎焊接头抗剪强度的影响

研究了加载速率对SnAgCu(SAC)无铅钎料钎焊接头抗剪强度和断裂模式的影响,试验钎料的Ag元素含量为1%～3%(质量分数),微拉剪接头的加载速率为0.01～10mm/s.结果表明,当加载速率小于1mm/s时,抗剪强度随加载速率的增大而增大,断裂模式为发生在接头钎料内部的延性断裂.当加载速率增大到10mm/s时,其抗剪强度反而减小,断裂模式为发生在界面金属间化合物层的脆性断裂.另外,在加载速率较低时,抗剪强度随Ag元素含量的增加而增加;但在较高加载速率下,Ag元素含量为2%的钎料接头抗剪强度最低.     

薄规格双金属复合板剪切强度的测试方法

参照GB/T6396-2008和ASTM A 264设计了薄规格双金属复合板抗剪强度的测试方法及装置,并对薄规格双金属复合板的抗剪强度进行了测试,与现有商品板的抗剪强度进行了对比和分析.结果表明:提出的测试方法简单实用和实验装置操作方便,测量误差小,数据离散度小,精度高,能准确评价薄规格双金属复合板的结合强度,测试结果符合GB/T6396-2008要求.     

真空热循环对环氧结构胶粘剂拉伸剪切性能的影响

本文利用空间环境效应地面模拟设备对环氧结构胶粘剂进行了真空热循环试验。采用MTS-810型材料试验机和扫描电子显微镜,研究了真空热循环下环氧结构胶粘剂拉伸剪切强度、延伸率和微观结构等变化规律。结果表明,随着热循环次数的增加,环氧结构胶粘剂的拉伸剪切强度呈先增强而后减弱的趋势。当热循环次数达到150次时,拉伸剪切强度达到最大值,比真空热循环前增加了16％。     

深海环境剪切模量测试系统的设计

为便于测试深海环境下材料的剪切模量,设计一套深海环境剪切模量测试系统。在分析深海环境模拟的基础上,提出一种基于高低温试验箱的温度与压力结合的闭环控制策略,完成深海环境模拟;基于微拉伸测试原理,设计剪切模量测试仪;利用ABAQUS软件对耐压舱与剪切模量测试仪进行有限元分析,确保在低温高压下的稳定运行;对测试装置进行标定分析,得到换能器频率与位移曲线。试验结果表明:耐压舱与剪切模量测试仪形变较小;同时测试得出了材料的剪切应力-应变曲线,测试系统具有较高的测量精度以及稳定性,能为以后深海环境测试提供一定的参考。     

超声横波法测厚与检验中非同质试块的应用

通过理论推导与实验、实测对比 ,论证了采用超声横波法对未知材质工件进行测厚的可行性及精确性。成功地将以任意一种已知对比试块为基准而调试的超声波检测系统用于任意未知材质的在役设备的壁厚测定和缺陷检验中 ,解决了超声横波法测厚与检验中非同质试块的应用问题 ,增强了在役设备检验中强度计算、安全分析及寿命预测的准确性     

Uniaxial Tensile and Simple Shear Behavior of Resistance Spot-Welded Dual-Phase Steel Joints

Small test coupons were machined from single spot welds in a dual-phase steel (DP600) to investigate deformation and failure of weld joints in both tension and shear. Quasi-static () testing was conducted in a miniature tensile stage with a custom image acquisition system. Strain accumulation in each weld was analyzed where fracture occurred, which was typically outside the fusion zone. A few shear test coupons that failed in the fusion zone were found to have the same spheroidal defects noted in previous work, and thus, severely limited weld strength and ductility. A novel strain mapping method based upon digital image correlation was employed to generate two-dimensional deformation maps, from which local stress-strain curves to failure were computed. As an important first step toward incorporation of material models into weld simulations, a preliminary finite element analysis of a tension test successfully reproduced the experimental results with material models for the base, heat-affected, and fusion zone materials generated from prior work.     

The Effect of Wetting Gravity Regime on Shear Strength of SAC and Sn-Pb Solder Lap Joints

The failure of solder joints due to imposed stresses in an electronic assembly is governed by shear bond strength. In the present study, the effect of wetting gravity regime on single-lap shear strength of Sn-0.3Ag-0.7Cu and Sn-2.5Ag-0.5Cu solder alloys reflowed between bare copper substrates as well as Ni-coated Cu substrates was investigated. Samples were reflowed for 10 s, T _gz (time corresponding to the end of gravity regime) and 100 s individually and tested for single-lap shear strength. The single-lap shear test was also carried out on eutectic Sn-Pb/Cu- and Sn-Pb/Ni-coated Cu specimens to compare the shear strength values obtained with those of lead-free alloys. The eutectic Sn-Pb showed significantly higher ultimate shear strength on bare Cu substrates when compared to Sn-Ag-Cu alloys. However, SAC alloys reflowed on nickel-coated copper substrate exhibited higher shear strength when compared to eutectic Sn-Pb/Ni-coated Cu specimens. All the substrate/solder/substrate lap joint specimens that were reflowed for the time corresponding to the end of gravity regime exhibited maximum ultimate shear strength.     

基于结构应力方法的正面角焊缝抗剪强度分析

建立了基于结构应力定义的正面角焊缝抗剪强度理论,给出了新的焊缝抗剪强度计算公式,并基于该理论对焊缝抗剪强度相关问题进行了分析.结果表明,单向受剪等焊脚正面角焊缝的断裂角度理论值为22.5°,焊趾角度和受力状态均会影响断裂角度.另外焊趾角度为30°的单向受剪焊缝具有最大的承载能力,而双向受剪焊缝的承载能力比单向受力时的承载能力也明显提高.试验数据证明了该理论的正确性,该理论也为焊缝尺寸设计提供了理论基础.     

New apparatus for characterising tensile strength development and hot cracking in the mushy zone

A novel apparatus for solidification research has been developed which utilises a modified tensile testing machine and customised mould to control thermal and mechanical parameters during solidification. The test provides constraint during solidification and generates information about strength development, strain accommodation and hot cracking behaviour of the mushy zone material. The equipment has been used to determine the effect of grain refinement and composition variations on these parameters. This paper describes the test apparatus and the type of information it generates. It includes a comparison of hot cracking produced in the rig with that obtained from direct chill cast product. The development of strength of a relatively pure material, alloy AA194, and a highly alloyed, extended freezing range alloy, AA7075 is presented. In the case of alloy AA7075 strength development began at a solid fraction of approximately 0.7 and continued to increase as solidification progressed. The development of strength in alloy AA194 did not occur until a fraction solid of 0.9. Under tensile loading conditions, the development of strength appears to occur at higher solid fractions than for rheological test methods.     

Shear Strength of Nickel Electroplated on some Difficult-to-Plate Metals

The adhesive strength of electroplated nickel on some of the difficult-to-plate metals such as titanium, stainless steel, and aluminium was measured using shear testing. Heavy nickel electrodeposits were produced on the above metals using different pre- and post-plating treatments. The work is a prelude to the electrochemical joining of these metals as required for space applications.