基于步进应力加速老化和改进Arrhenius模型的橡胶贮存寿命预测

为准确、快速地预测橡胶的贮存寿命,在步进高温应力加速老化试验的基础上,对不同加速温度下的加速系数进行计算,获得加速因子和绝对温度倒数的曲线,发现橡胶老化过程表现出非Arrhenius特性。针对非Arrhenius特性,引入幂指数因子,采用一种改进的Arrhenius模型对加速系数进行拟合。由对数反应速率与绝对温度倒数曲线的斜率,计算了改进Arrhenius模型在不同温度下的等效线性活化能,结果表明低温下活化能减小。建立低温下的老化寿命模型,对胶料在10℃,20℃和30℃下的老化寿命进行评估。评估结果表明,该模型可为相关高分子材料腐蚀过程中呈现的非Arrhenius特性的分析及寿命预测提供参考。     

The military as a learning organisation: establishing the fundamentals of best-practice in lessons-learned

The post-Cold War era has witnessed the rapid expansion of organisational learning initiatives within NATO militaries, especially formal “lessons-learned” processes. The effectiveness of national lessons-learned processes in recalibrating military activity to the demands of ongoing operations has been highly-differentiated. However, the academic literature on military change and practitioner guidance has been slow to investigate the key features of best-practice in military learning. This article breaks new ground by drawing upon the literature on dynamic organisational capabilities to explore the fundamental organisational processes and activities which are necessary to implement successful lessons-learned. It examines, in particular, the organisational features which facilitate “knowledge transformation”: the effective combination of new knowledge gained from intra- and inter-organisational learning with existing organisational knowledge. The article concludes by highlighting several potential future empirical and theoretical research agendas in military learning and the importance of engagement between lessons-learned practitioners and organisational learning scholars.     

B4C／Al复合板中应力波行为分析（Ⅱ）

在已建立的应力波传播模型和研究弹、板间作用力所获结果的基础上,为分析复合板应力的变化,对复合板弹板碰撞承受的应力进行了简化处理,根据应力波传播特性,确定了复合板内能量集中区域,研究了应力波在复合板巾的传播和能耗,并讨论了应力波对陶瓷的作用。通过近似计算,发现烧蚀消耗的弹丸动能较大,在复合板中,Al板的塑性变形吸收了19％的弹丸动能。     

地下工程预备口开挖的静力有限元分析

预备口对提高地下工程的生存能力有着重要影响,针对其特殊构造形式,运用有限元软件ANSYS进行三维数值模拟,分析预备口开挖过程中围岩应力和变形的分布规律。开挖过程中,围岩应力及时释放并重新分布,拱顶下沉变形最大,侧墙中点横向变形较明显;侧墙与底板交界处应力集中,预留掌子面处应力和轴向变形较其他断面要弱。为今后的施工提供借鉴。为今后的施工提供借鉴。     

岩质边坡开挖应力与变形的有限元模拟

采用非线形有限元数值模拟的方法,对岩质边坡开挖进行了数值分析。利用有限元软件ANSYS提供的单元生死功能模拟了重庆市某边坡锚杆挡墙工程逆作法施工的全过程,给出了其应力和变形的分布曲线,并对其应力和变形与未加锚时做了分析比较。算例表明,加入锚杆后边坡体上部水平位移分布曲线趋于平缓,在距坡脚约三分之一坡高的地方,比未加锚的水平位移值减少了15％。     

自增强厚壁圆筒残余应力分布规律研究

以火炮身管自增强处理为背景 ,根据炮钢材料实际的拉伸—压缩试验曲线和性能参数 ,将Bauschinger效应系数和强化效应系数作为加载阶段产生的相当塑性应变的函数 ,对厚壁圆筒自增强处理产生的残余应力分布规律进行了理论分析和实验研究。     

软硬交替多层膜法向压入过程的有限元分析

采用大变形弹塑性有限单元法,对高速钢基体上的软硬交替多层膜在法向压痕作用下的力学行为,进行了模拟和分析.为了研究膜层数和膜厚的影响,对从单层到16层的不同膜层体系进行了计算.通过对诸如膜层的变形、最大应力随膜层数的变化、界面剪应力分布、表面张应力分布等的分析,得出了这些参数的分布及其对膜层体系的摩擦学性能的影响.这些结果可为多层膜的结构优化设计提供定量的依据.     

High strain rate deformation of explosion-welded Ti6Al4V/pure titanium

Multilayer materials are widely used in military, automobile and aerospace industries. In this paper, the response of an explosion-welded Ti6Al4V/pure titanium with a flat interface to dynamic loading is investigated. An SHPB apparatus is used. Then, the dynamic behaviour of a bimetal sample is explored with a DIC system coupled to the SHPB. Result indicates that in the bimetal sample pure titanium is deformed and failed before Ti6Al4V. The stress curve of the sample shows two different peaks in a striker velocity higher than the 18.3 m/s. When the incident wave encounters the interface of the Ti6Al4V/pure titanium sample, only a small fraction of the wave is reflected owing to similar impedance. Using the direct interpretation stress-strain curve is unreasonable in this case because of unhomogenised plastic deformation. The microstructure of the sample is investigated after loading. An adiabatic shear band is formed in the pure titanium side before failure, and the interface of the sample remains intact under different loading conditions. The FEM simulation result for the sample is in good agreement with experimental observations.     

Experimental investigation on dynamic response and damage models of circular RC columns subjected to underwater explosions

Reinforced concrete (RC) columns are widely used as supporting structures for high-piled wharfs. The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharf’s antiknock security. In this study, the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models. Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m, under different explosive quantities (0.025 kg–1.6 kg), stand-off distances (0.0 m–7.0 m), and detonation depths (0.25 m–2.0 m). The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure, acceleration, strain, and displacement. Then, the load distribution characteristics, time history of test data, and damage models related to present conditions were obtained and discussed. Three damage models, including bending failure, bending-shear failure and punching failure, were identified. In addition, the experience model of shock wave loads on the surface of a RC column was proposed for engineering application.     

Responses of HFR-LWC beams under close-range blast loadings accompanying membrane action

The load-carrying capacities and failure patterns of reinforced concrete components can be significantly changed by membrane effects. However, limited work has been carried out to investigate the blast resistance of Hybrid Fiber Reinforced Lightweight Aggregate Concrete (HFR-LWC) members accompanying membrane action. This paper presents a theoretical approach to quantitatively depicting the membrane behavior and its contribution on the behavior of HFR-LWC beams under close-range blast loadings, and the suitability of the proposed model is validated by a series of field tests. An improved Single-Degree-of-Freedom (SDOF) model was employed to describe the dynamic responses of beam-like members under blast loadings accompanying membrane action, where the mass-load coefficient is determined according to the nonuniformly distributed load induced by close-range explosion, and the membrane action is characterized by an in-plane (longitudinal) force and a resisting moment. The elasto-plastic and recovery responses of HFR-LWC beams under the combined action of blast load and membrane force were analyzed by the promoted model. A specially built end-constrain clamp was developed to provide membrane action for the beam member when they are subjected to blast load simultaneously. It is demonstrated that the analytical displacement-time histories are in good agreement with experimental results before peak deflections and that the improved SDOF model is an acceptable tool for predicting the behavior of HFR-LWC beams under blast loadings accompanying membrane action.