QP980高强钢板杨氏模量测定方法研究

通过单向循环加载-卸载试验,研究了杨氏模量的测定方法及QP980高强钢板杨氏模量随塑性变形的变化规律,并与材料参数优化方法获得的杨氏模量值进行对比。结果表明,在用拟合的方法来获取材料的杨氏模量时,拟合数据段应力水平不同,得到的杨氏模量数值也不同,而利用拟合相关系数随应力水平的变化规律,能较好的确定拟合数据段的应力水平,从而得到准确的杨氏模量数值。对于QP980高强钢板杨氏模量的变化规律而言,随卸载点真实应变的增加,杨氏模量逐渐减小,并最终趋于稳定。

Experimental investigation on damage evolution behaviour of a granitic rock under loading and unloading

In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of rock structures. In this paper, we investigate the damage evolution characteristics of a granitic rock during loading and unloading after a series of triaxial experiments performed at different confining pressures. The axial stress-axial strain variations of the tested specimens revealed that the specimens undergoing unloading fail with a lower axial strain compared to the specimens failed purely by loading. Higher confining pressures were observed to exacerbate the difference. Volumetric strain versus axial strain curves indicated that the curves reverse the trend with the beginning of major damage of specimens. We suggest here a new form of equation to describe the secant modulus variation of brittle rocks against the axial stress for the unloading process. Failure mechanisms of tested specimens showed two distinct patterns, namely, specimens under pure loading failed with a single distinct shear fracture while for the unloading case specimens displayed multiple intersecting fractures. In addition, analysis of the evolution of dissipation and elastic energy during deformation of the specimens under loading and unloading conditions showed differentiable characteristics. Moreover, we evaluated the variations of two damage indices defined based on the energy dissipation and secant modulus evolution during deformation and observed that both of them satisfactorily distinguish key stages of damage evolution.

火焰复合层对化学交联聚乙烯发泡材料力学性能的影响

化学交联聚乙烯发泡材料（Cross-linked polyethylene,XPE）具有优异的物理、化学与力学性能,被广泛应用于工业领域。本文通过对不同层数的XPE发泡材料进行加载-卸载试验与压缩循环试验,得到不同层数XPE发泡材料的应力-应变曲线,获得了弹性区与平台区分界点的应力与应变、平台区与强化区应力的数量关系。通过计算得出应力-应变环的面积,发现其能量耗散能力随加载次数增加呈现下降趋势。结果表明,单层XPE发泡材料的弹性区与平台区弹性极限应变、临界应力强度和应力环面积等性质与多层材料相比差别显著,而多层材料间力学性能的差异微小。这些特征表明,火焰复合层自身具有较大的刚度并对发泡材料孔壁有较强的约束,改善了XPE发泡材料的刚度、弹性模量及耗能能力等。