前期动载对低塑性粉土静态和动态强度的影响

 低塑性粉土广泛存在于世界范围内,在地震中容易产生液化现象,然而一些基础设施破坏不仅见于地震中也发生在地震后,这就决定了研究低塑性粉土震后行为的必要性。以美国中部密西西比河沿岸低塑性粉土为试验材料,研究动载对低塑性粉土静态和动态强度的影响。在动三轴仪上对试样施加动载引起超孔隙水压力,排水重固结后,分别对2组震动后试样进行静态和动态三轴强度试验。试验结果表明,当液化水平小于0.70时,前期动载对粉土的不排水剪切强度影响不大;相反地,只有当液化水平大于0.70,密西西比河沿岸粉土的震后重固结体积应变和不排水剪切强度才伴随着液化水平的提高显著增加,但相对于砂土而言,重固结体积应变在较低的液化水平时即有明显增加。与前期动载对不排水剪切强度的影响不同,当动载所引起的液化水平为0.35或轴向应变为0.2%时,抗液化强度达到最大值,若液化水平大于0.35,抗液化强度伴随液化水平提高而降低。如果前期荷载引起较大的压应变,在重固结后第二次动载循环中,轴向压力相比轴向拉力引起较小的超孔隙水压力。     

锆-钛-钢复合板界面损伤机理及表面耐腐蚀性能

运用内聚力模型研究了锆-钛-钢复合板在粘结试验中的界面损伤过程,并利用扫描电子显微镜分析了界面断裂机理。运用正交试验研究了不同热处理工艺条件下的表面耐腐蚀性能,分析了保温温度、保温时间和升降温速率对粘结性能的影响。结果表明,I型裂纹加载下,界面损伤由内壁处开始,并逐渐发展至整个界面。界面整体属于脆性断裂,而波峰与波谷的过渡斜面则为混合断裂。腐蚀试验的塔菲尔极化曲线研究结果表明,锆覆层在HCl溶液中以点腐蚀为主,而在HAc溶液中以均匀腐蚀为主。爆炸焊接后,锆复合板的耐点腐蚀性能低于纯锆材料,并且保温温度越高,保温时间越长,耐腐蚀性能下降越明显。     

The influence of the internal structure of core–shell particles on poly(vinyl chloride)/(methyl methacrylate–butadiene–styrene) blends

Methyl methacrylate–butadiene–styrene (MBS) core–shell particles were prepared by grafting styrene and methyl methacrylate onto polybutadiene seeds via emulsion polymerization. All the MBS particles were designed with the same chemical composition, similar grafting degree but different internal structures. The difference in internal structure was realized by controlling the ratio of ‘external grafting’ and ‘internal grafting’ of styrene. The work focused on the influence of the internal structure of MBS core–shell particles on the properties of poly(vinyl chloride)/MBS blends. From transmission electron microscopy, three different internal structures were observed: rare sub‐inclusions, a large number of small sub‐inclusions and large sub‐inclusions. The results of dynamic mechanical analysis illustrated that the different internal structures greatly affected the glass transition temperature T_g of the rubber phase and the storage modulus of the core–shell particles. The notched Izod impact test results showed that the MBS with large sub‐inclusions had the lowest brittle–ductile transition temperature, while the transparency test revealed that the presence of sub‐inclusions in the rubbery phase reduced the transparency of the blend. Copyright © 2012 Society of Chemical Industry     

The influence of skill and low back pain on trunk postures and low back loads of shearers

Shearing is a rural occupation developing considerable spinal loads and carrying a high risk of low back pain (LBP). Although the workforce has a skill structure, interaction between skill, spinal loads and LBP is unknown. We examined whether skill and LBP influenced trunk postures and loads within a sample of 80 shearers representing shear skill levels. A progression from junior to open class demonstrated a 100% increase in productivity, less time in severe flexion, more time in neutral lateral bend, and more time in axially twisted postures, with no increase in cumulative compressive and anterior shear forces. LBP prevalence increased linearly from 10% for junior through to 76% for open class shearers. Shearers with a history of LBP generated greater cumulative right medio-lateral shear forces, greater left lateral bend and left axial twist moments. Skill-based training that reduces asymmetric forces may help reduce such high prevalence levels of LBP.

Statement of Relevance: Shearing is an important and physically demanding rural occupation. It requires sustained flexed postures that generate considerable spinal loads and a high risk of LBP. This research examines how skill and a history of LBP it carries interact to influence trunk postures and spinal loads within a sample of shearers.     

某露天矿区全风化花岗岩原位试验研究

针对南方某露天矿区全风化花岗岩进行现场原位试验,选择制备了3组代表性的全风化花岗岩试体,通过设计堆载对试体加载不同垂直荷载的正应力、水平剪应力,直至剪切破坏的试验,对试验数据整理分析,获得正应力σ和正应变ε曲线图、剪应力τ和剪应变ε曲线图,用最小二乘法回归得出抗剪强度曲线图和C、φ值及相关系数R;根据试验施加的单位压力P和实测的岩体变形S,绘制P-S关系曲线,得出弹性(变形)模量。为采场边坡稳定性计算分析提供更符合实际的岩土力学参数,也为工程中遇到类似的风化花岗岩时提供参考。     

Characterization of mechanically sheared edges of dual phase steels

In recent years advanced high strength steels (AHSS) received increased interest for light structures with improved performance, but they are often sensitive to edge cracking during sheet metal forming. In this study mechanically sheared edges were characterized for three dual phase steels (DP600, DP780 and DP980), sheared with three die clearances (5%t, 10%t, 15%t) and along rolling and transverse directions. Microstructures of the materials were provided first, and then the sheared edges were examined by optical microscopy and scanning electron microscopy that reveal the morphology and random feature of the sheared edges. A factorial analysis was performed to reveal the general trends of the processing parameters on four edge zones. A new strain measurement method was used for characterizing strain distribution in the sheared region, which shows the peak strain to be higher than 3. The strain quickly decreases from sheared edge to interior, leaving a shear-affected zone of about 500 μm or 31% of the thickness. The fracture processes and involved mechanisms were discussed.     

浮动式液压剪的结构特点及参数计算

本文结合作者的浮动式液压剪的设计、调试体会,分析了液压剪的结构组成,并对液压剪设计所需的一些重要参数进行确定。     

Effect of periodic melt shearing process and cooling rate on structure and hardness of Al–0.7Fe aluminum alloy

In this investigation, the effect of periodic melt shearing process and cooling rate on an Al–Fe alloy was studied. Microstructural examinations were conducted by X-ray diffraction, optical and scanning electron microscopy coupled with energy dispersive spectrometry (EDS). Experimental results suggest that shearing above melting point can refine the alloy structure and improve the morphology of intermetallic phases and; the level of refinement is increased by increase of shearing time. Also, increasing cooling rate through reduced sections, decreases grain size and secondary dendrite arm spacing (SDAS) and improves the microstructure of Al–Fe alloy. The results of hardness test showed that increasing cooling rate and time of melt shearing reduce the hardness of Al–Fe alloy.     

空气和腐蚀环境下双相不锈钢SAF2507的疲劳性能

对超级双相不锈钢SAF2507分别在空气和3.5%NaCl溶液中进行旋转弯曲疲劳实验,研究两种介质下SAF2507不锈钢的疲劳性能。结果表明:宏观上,双相不锈钢SAF2507在3.5%NaCl腐蚀环境中的疲劳强度较空气中的下降幅度小,为空气下的90%。但微观上,空气中疲劳断口表现为韧性断裂,在铁素体和奥氏体相上呈现大量疲劳辉纹;腐蚀环境下,奥氏体为韧性断裂,而铁素体呈现解理断裂模式。两相上疲劳辉纹的宽度和间距随着晶粒位向及二次裂纹的开裂而不同。在奥氏体-铁素体双相不锈钢的疲劳断口中,不能根据疲劳辉纹的间距进行相的鉴别。