冲击拉伸过程中HDPE银纹内聚力的测定

热塑性聚合物经受稳定的银纹微纤拉伸时,银纹区的迅速增厚将会迅速地引起局部绝热升温现象.预测裂尖银纹的热力学分析可以预测结晶热塑性高聚物冲击断裂阻抗.热反内聚模型用来模拟冲击拉伸过程银纹寿命或反内聚时间.文中报道了一种新型的全切痕蠕变测试法可以在银纹增厚速率高达2m/s时测量平面银纹层的内聚力,在快速拉伸条件下高密度聚乙烯的内聚力和银纹寿命被测量,测试的结果与数值模型的预测结果是相一致的.     

航空有机玻璃银纹分析及预防措施

航空有机玻璃广泛应用于飞机座舱盖透明件,本文从分析其材质特性入手,研究其产生银纹的原因,进而分析其预防措施。     

M22机用丝锥产生裂纹的原因分析与探讨

在M22机用丝锥蒸汽处理后发现有批量的产品存在裂纹,经过分析认为:裂纹产生于机加工的磨槽工序,磨削过程中产生了加工变质层,导致产生了磨削应力。在机加工后,磨削应力转变成残余磨削应力,磨削应力以及残余磨削应力的本质是拉应力,应力在丝锥牙根处集中导致裂纹的产生和扩展。     

GCr15轴承钢连铸圆坯表面裂纹产生原因及防止措施

本文详细讨论了包钢GCr15轴承钢φ180 mm连铸圆坯表面裂纹的特征及其产生原因.该铸坯表面裂纹系拉坯过程中铸坯表面与铜质结晶器发生摩擦,导致铸坯表面渗铜而产生的铜脆裂纹,并据此提出了相应的防止措施.     

高聚物银纹断裂的研究现状

银纹化是高聚物的一种非线性变形方式，对高聚物的增韧设计十分重要。考虑银纹细观结构特征的银纹生长和断裂规律是研究银纹增韧机制的核心内容。结合国内外最新的研究进展，对承载高聚物中的银纹断裂及其与裂纹扩展的相互作用等问题作了较全面的总结和分析，并对今后的研究重点和趋势作了简要展望。     

The micromechanics and microstructure of CO2 crazes in polystyrene

Although CO₂ at 1 atmosphere pressure is not a crazing and/or cracking agent for polystyrene (PS), we have established that it becomes one at higher pressure. Crazes grown from cracks in PS thin films in high pressure CO₂ are investigated using transmission electron microscopy (TEM). The fact that broken craze fibrils retract strongly upon exposure to high pressure CO₂ gas suggests that the primary effect of the CO₂ is plasticization, not surface energy reduction. Quantitative analyses of TEM micrographs of crazes grown at CO₂ pressures in the range 5 to 100 MPa at 34°C and 45°C have been carried out to find the craze fibril volume fractions v_f(x) and the surface displacements w(x) along each craze. From the fibril volume fraction profile along the craze, the dominant craze thickening mechanism of CO₂ crazes is shown to be the same as that for air crazes, i.e. the surface drawing mechanism, and not the fibril creep mechanism. The craze surface stress profile is computed from the craze surface displacements using a distributed dislocation analysis. These profiles all show a stress concentration at the craze tip which falls to a roughly constant value σ_b, over the rest of the craze. The fracture toughness G_Ic (and critical stress intensity factor K_Ic) for propagation of a crack in PS at these CO₂ pressures can also be computed. All these quantities (V_f, σ_b, G_Ic and K_Ic) show pronounced minima as a function of CO₂ pressure at 20 MPa, the same CO₂ pressure at which T_g of the polymer also reaches a minimum. These minima are more pronounced at 45°C than at 34°C. The G_Ic's and K_Ic's are depressed by orders of magnitude at the minimum, which corresponds to the qualitative observation that CO₂ becomes a severe cracking agent at these pressures. These observations provide additional confirmation that the major mechanism for the environmental crazing and cracking of PS by CO₂ is plasticization of the craze fibrils and surfaces.     

Effect of strain history on craze microstructure

Crazes formed under a constant tensile strain in polystyrene (PS) have a dense network of fibrils with an extension ratio $\text{λ ? 4}$, but a midrib of higher λ forms by drawing fibrils from the craze-matrix interface in the high stress region just behind the craze tip. Stepwise increases in tensile strain during craze growth should thus produce layers of fibrils of different λ, which can be revealed by transmission electron microscopy (TEM) of crazes in stepwise strained PS films. When the time interval between strain increments of 0.5–1% is one minute, TEM images show ‘ridges’ of lower λ fibrils, corresponding to the position of the craze-matrix interface at the time of the strain increments. The ridges appear to be the analogue of the bulge remaining on a macroscopic fibre which has been allowed to stress age by stress relaxation before resuming drawing and imply that rapid stress ageing must occur near rthe craze-matrix interface so that more material is drawn into the craze in preference to increasing the λ of the existing fibrils.     

纳米碳酸钙在密封剂中的应用

综述了纳米碳酸钙在密封剂中的应用及研究现状。着重介绍了纳米碳酸钙的制备过程中对生产工艺和原料的要求。通过“裂缝与银纹相互转化”机理解释了纳米碳酸钙对密封剂的增强机理和作用。提出了纳米粒子在有机介质中,由微观的“微海效应”导致的宏观的触变性的设想。介绍了纳米碳酸钙在密封剂中应用前所需的表面化学改性及表面物理包敷改性,应用中的物理机械分散及原位聚合。并阐述了不同的条件下纳米碳酸钙对密封剂的伸长率、拉伸强度、动态力学等性能的影响。     

高分子材料银纹研究

结合国内外研究状况,对银纹结构、引发、生长以及断裂进行了全面的介绍和分析,总结了近年来对银纹认识的发展,并对今后研究的重点和趋势进行了展望。     

选煤厂振动筛侧板开裂的修复及原因分析

介绍了选煤厂振动筛侧板开裂的修复方法,并从制造、安装、使用和维护等方面对侧板开裂原因进行了分析,指出采用铆接工艺对翼板、加强板和侧板进行联接,严格按照安装标准进行安装,保证给料连续和均匀,及时更换弹簧,保持原设计对动力学因素的要求等,是预防开裂的主要措施。