循环爆破作用下岩体的不同步累积损伤测试方法

为了提高循环爆破载荷作用下岩体累积损伤测试方法的精确度、预测结果的可信值以及控制标准的规范化,提出不同步累积损伤测试方法。采用理论分析与现场实践相结合的方法,基于5次循环爆破载荷作用下不同测孔深度处声波速度的变化规律,依据损伤度与声波速度的关系式,对比分析2种测试方法的累积损伤效应。研究结果表明:循环爆破载荷仅对测孔孔口至1.6 m处岩体区域产生损伤效应,并且垂直于掌子面的剖面区域所受的累积损伤最为严重;不同步测试方法所得的岩体累积损伤效应更加明显,且累积损伤-爆破次数关系曲线更加光滑,由此证明,不同步累积损伤测试方法能够提高测试精度,增加拟合曲线的可信程度,不仅为支护厚度提供依据,而且为支护方向提供参考。     

轧制温度和累积应变对累积叠轧焊AZ31镁合金板材组织和性能的影响

通过光学显微镜（OM）、扫描电镜（SEM）和力学性能检测,研究了AZ31镁合金在不同温度和累积应变条件下累积叠轧后的微观组织和力学性能。结果表明：晶粒尺寸随累积叠轧温度降低和累积应变增加而减小;经过3道次的ARB变形后,晶粒细化不再显著,但是组织均匀性得到改善。300℃以上的ARB变形对AZ31板材的强度和延性均有一定...     

Networks and Rapid Technological Change: Novel Evidence from the Canadian Biotech Industry

Former studies on inter-organizational relationships have fallen short of properly identifying networks and elucidating factors that cause firms to entertain relationships in one type of network rather than another. This study adopts a methodology that is both empirical and comparative and thus constitutes a methodological departure from these previous studies. It also explicitly accounts for two structural characteristics of networks, namely, interactions and learning, to identify four types of networks, accumulative advantage networks, follow-the-trend networks, homophilies and multiconnectivity networks. It then investigates factors that cause firms to participate in any of these networks rather than another. Results show that even though networking is a common practice among biotech firms, most of them would rather keep this activity to a minimum. In addition, participation in these networks is found to vary according to the firm's size, stage of development and its sector of activity.     

Influence of the thermomechanical processing on the fracture mechanisms of high strength aluminium/pure aluminium multilayer laminate materials

The microstructure and mechanical properties, with emphasis in the impact fracture toughness behaviour, of two multilayer laminate materials have been investigated. The multilayer materials are constituted by alternated sheets of pure aluminium (Al 1200 or Al 1050) and high strength Al 7075 alloy. Stacked layers of these alloys have been successfully joined using two processing routes with different total hot rolling strains. Both laminates have been tested at room temperature under impact Charpy tests, three-point bend tests and shear tests on the interfaces. Both laminates exhibited more than eight times improvement in impact fracture toughness over the monolithic Al 7075-T6. The toughness increase in the higher rolling strained laminate is almost entirely due to crack blunting mechanism, while in the lower strained laminate, crack deflection by delamination and crack renucleation processes were active.     

异步叠轧铜板的再结晶研究

对七道次异步叠轧铜板采用220℃×30 m in和220℃×40 m in两种退火工艺,运用背散射电子衍射技术(EBSD)对两种铜板的再结晶程度、极图和织构进行了研究.结果表明:采用220℃×40 m in退火工艺的铜板再结晶较完全,其织构为明显的{100}〈001〉立方织构;而采用220℃×30 m in退火工艺的铜板内仍存在晶体缺陷,其织构为{123}〈412〉轧制织构,及少量的{100}〈001〉立方织构.     

TA1/Q235钢累积叠压变形特性及界面组织

采用累积叠轧压方法,研究了TA1/Q235钢累积叠压变形特性及界面组织.研究结果表明:随着总应变的增加,TA1与Q235钢的变形程度的差别增大,当真应变大于1.0时二者的变形差基本上维持在1.0左右.TA1的应变在850~900℃范围内发生突变,并伴随着径向变形差值增大.当变形温度小于850℃时,在Q235钢侧,呈现出非常明显的垂直于压缩方向的变形组织;当复合变形温度为850~950℃时,在Q235钢侧出现了明显的铁素体柱状晶组织,晶粒排列整齐,几乎都垂直于界面,并且随着温度升高,铁素体晶粒粗化.当累积变形量小于1.5、变形温度为850℃时,金属间化合物的厚度为0.7~1μm,当累积变形量为2.0时厚度约1.7μm.当累积变形量为1.0时,在700~850℃条件下压制,界面化合物层厚度变化不大,为0.8~1μm,900℃时其厚度增加了1倍多,950℃时达到约2.3μm.     

螺纹中径当量的全微分优化逼近算法及图形仿真

本文建立的螺纹中径当量全微分优化逼近模型，考虑了螺距偏差，螺距累积偏差和半角偏差本身及其相互间对中径的综合影响，并用理想螺纹在径向和轴向二维逼近实际螺纹，计算机计算表明，本文提出了全微分优化逼近算法优于常用算法及三点接触式算法，经计算机图形仿真显示算法是正确的。     

4A60铝/08Al钢复合带材冷轧结合行为的研究

以冷轧薄包覆层(100μm)4A60铝/08Al钢复合带材的变形区为研究对象,借助金相显微镜、扫描电镜及硬度计等实验手段,对铝/钢轧制复合变形区的金属变形行为和结合性能进行了研究。结果表明:铝/钢轧制复合过程中从入口到出口可分为3个变形区,即铝和钢变形但未复合区、铝和钢变形且复合区和钢变形而铝不变形的稳定复合区;从复合比变化的角度并参考界面结合行为确定薄包覆层4A60铝/08Al钢复合带材的临界复合压下量为15%左右,最小复合压下量为35%左右。     

循环荷载作用下软土中吸力锚变形过程拟动力算法

针对静荷载与循环荷载共同作用下软土中张紧式吸力锚的变形失稳过程进行了研究,通过拟动力有限元法模拟了静荷载和循环荷载共同作用下模型锚变形过程,验证了拟动力算法的可行性。分析过程中采用考虑循环荷载作用历史的等效线性黏弹性计算模型描述饱和软黏土不排水循环动力响应,依据蠕变理论描述土单元的循环累积应变响应。基于ABAQUS有限元软件,借助拟动力黏弹塑性模型提出了一种既能描述土体循环动力响应又能获得土体变形循环累积过程的拟动力算法。通过编制脚本程序PYTHON,将计算土体循环动力响应的过程与分析土体变形累积的过程连接起来,使计算机自动完成整个拟动力有限元算法的分析过程,最终实现了不通过详细跟踪循环荷载作用历史即可获得软土中吸力锚在循环荷载作用下变形逐渐循环累积至失稳过程的拟动力算法。     

金属间化合物对累积叠轧Mg/Al多层复合板材断裂过程的影响

本文采用分步拉伸观测的方法研究了累积叠轧Mg/Al多层复合板材中界面金属间化合物对复合板材断裂过程的影响。结果表明：在单向拉伸过程中,Mg/Al界面处金属间化合物导致了裂纹的萌生和扩展,从而导致Mg/Al界面的分离;在后续拉伸过程当中,由于Mg层强度较低,首先产生颈缩失效,致使整个样品提前断裂。