应力波在泡沫铝夹层三明治板中传播规律的数值研究

根据 Gibson 理论模型确定出泡沫铝的力学参数,设计出不同密度组合的5种数值计算模型,利用非线性动力学程序 LS-DYNA 研究了爆炸载荷作用下,应力波在泡沫铝夹层三明治板中的传播规律。对其缓冲吸能、衰减应力波特性进行对比分析。研究结果表明：由 Gibson 理论模型确定出的泡沫铝力学参数,在 CrushableFoam 本构模型中能够较好地反映应力波在不同介质界面间的反射与透射情况,与弹性波理论吻合度较高。在总体密度相同的情况下,H-M-S 梯度结构对爆炸冲击波具有更好的缓冲效果。其对应力波的持续削弱能力和爆炸冲击能量的持续吸收能力都要强于其他结构。     

不同介质中集团装药爆炸混凝土冲击响应的数值模拟

基于非线性有限元软件ANSYS/LS-DYNA,选用Holmquist-Johnson-Cook损伤本构模型,对不同介质中集团装药爆炸下混凝土的动态响应进行了数值模拟,研究了装药在不同介质中爆炸对混凝土的冲击响应和爆炸波在混凝土内的传播与衰减规律。结果表明,介质对混凝土内应力场、压力场、损伤和速度场的分布与衰减有着十分明显的影响。     

不同介质中集团装药爆炸混凝土冲击响应的数值模拟

基于非线性有限元软件ANSYS/LS-DYNA,选用Holmquist-Johnson-Cook损伤本构模型,对不同介质中集团装药爆炸下混凝土的动态响应进行了数值模拟,研究了装药在不同介质中爆炸对混凝土的冲击响应和爆炸波在混凝土内的传播与衰减规律。结果表明,介质对混凝土内应力场、压力场、损伤和速度场的分布与衰减有着十分明显的影响。     

硬岩中爆炸冲击波衰减规律的数值模拟

利用ANSYS/LS-DYNA有限元分析软件,建立了硬岩介质中装药爆炸的数学模型,对硬岩体中的爆炸冲击波的传播衰减规律进行了数值计算。数值计算模型计算得到的爆炸冲击波压力与经验公式计算的冲击波压力数据基本一致,验证了该模型的正确性。     

基于爆炸振动波的黄土中空腔坑定位研究

靶场地下常会有弹坑或弹道坑等,有时需要对它们的位置进行判断,但实际中并没有很好的办法来解决这个问题.由于土壤介质的复杂性和多样性,很难有统一的方法来预测其位置,特别是土壤的静态和动态力学参数,只能针对具体的土壤去分析.本文针对我国渭河滩黄土土壤,通过试验研究爆炸波引起的黄土土壤爆炸坑洞的形成和振动传播规律测量,结合土中爆炸力学的理论分析结果,给出黄土土壤中一些爆炸作用的特征参数的估算方法和爆炸或弹道坑空腔的定位方法.     

球形装药半无限土介质中爆炸动力学分析

通过对球形装药土中爆炸的数值模拟,研究了球形装药半无限土介质中爆炸作用下,土介质的动力学响应;空腔的形成发展规律及鼓包的运动规律等动力学问题．数值模拟结果与实验现象吻合较好。     

水下爆炸应力波在含声学覆盖层结构中的传播规律

 针对舰船的含声学覆盖层结构,对水下爆炸作用下应力波在该结构中的传播规律进行研究。采用二阶Godunov方法,建立水下爆炸应力波在多层介质中传播的计算模型,并与经典Taylor平板解析解进行对比验证;通过对不同工况下的应力波传播规律分析,获得边界条件、声学覆盖层厚度等参数对其影响规律,可为舰艇抗冲击设计、研究提供参考。     

冰介质爆破特性实验研究

迄今 ,由于缺乏对冰介质爆破特性的了解 ,黄河防凌爆破仍停留在局部经验阶段。本文对冰介质的力学特性进行了实验研究 ,并测定了部分力学特性。结果表明 ,在爆炸载荷作用下 ,冰介质呈现明显的脆性变形 ,并且其抗压强度是抗拉强度的 3～ 6倍。通过 -2 5℃气温条件下冰介质中标准爆破漏斗试验 ,求得炸药单耗为 83 0 g/m3,与爆破中软岩石的炸药单耗相当。     

冰介质爆破特性实验研究

迄今 ,由于缺乏对冰介质爆破特性的了解 ,黄河防凌爆破仍停留在局部经验阶段。本文对冰介质的力学特性进行了实验研究 ,并测定了部分力学特性。结果表明 ,在爆炸载荷作用下 ,冰介质呈现明显的脆性变形 ,并且其抗压强度是抗拉强度的 3～ 6倍。通过 -2 5℃气温条件下冰介质中标准爆破漏斗试验 ,求得炸药单耗为 83 0 g/m3,与爆破中软岩石的炸药单耗相当。     

台阶爆破充填物的运动分析

用力学原理及爆炸力学理论推导出台阶爆破中炮孔充填物的运动规律，所得的规律五实验结果相吻合，分析了充填物的运动规律，推导的结果可用于炮孔充填长度的确定。     

FSI modeling with the DSD/SST method for the fluid and finite difference method for the structure

We present a fluid–structure interaction (FSI) modeling method based on using the deforming-spatial-domain/stabilized space–time (DSD/SST) method for the fluid mechanics part and a finite difference (FD) method for the structural mechanics part. As the structural mechanics model, we focus on the thin-shell model. The fluid mechanics equations with moving boundaries are solved with the DSD/SST method and the thin-shell structural mechanics equation is solved with a FD method, with partitioned coupling between the two parts. The coupling of the DSD/SST and FD solvers makes sure that the boundary conditions on the fluid-structure interface at the end of each time step are matched between the fluid and the structure. A hanging plate in vacuum under gravitational force is performed to validate the structure solver. In addition, a pitching plate in a uniform flow is simulated to validate the FSI solver. The present results are in reasonable agreement with data predicted by other methods.     

颗粒流动模型研究进展

颗粒流动在自然界中和各种工业过程中广泛存在,但人们对于其机理认识的还不深入。描述颗粒运动的模型有很多,连续介质模型应用简单但准确性比较低,离散微粒学模型是近来人们研究的一个热点,以每个颗粒为考察对象,能够更准确地反应颗粒系统的性质。本文介绍了描述颗粒流动的模型,概述了各模型的理论和应用,通过对多种模型的比较可以看到,每个模型都有一定的使用范围,要更准确、更方便地描述颗粒系统的运动,还要进行深入地研究。     

Interface fracture in adhesively bonded shell structures

Two methods for the prediction of crack propagation through the interface of adhesively bonded shells are discussed. One is based on a fracture mechanics approach; the other is based on a cohesive zone approach. Attention is focussed on predicting the shape of the crack front and the critical stress required to propagate the crack under quasi-static conditions. The fracture mechanical model is theoretically sound and it is accurate and numerically stable. The cohesive zone model has some advantages over the fracture mechanics based model. It is easier to generalise the cohesive zone model to take into account effects such as plastic deformation in the adhering shells, and to take into account effects of large local curvatures of the interface crack front. The comparison shows a convergence of the results based on the cohesive zone model towards the results based on a fracture mechanics approach in the limit where the size of the cohesive zone becomes smaller than other relevant geometrical lengths for the problem. However, convergence issues and numerical stability must be addressed.     

A numerical study on the impact resistance of composite shells using an energy based failure model

This paper presents a numerical study on the impact resistance of composite shells laminates using an energy based failure model. The damage model formulation is based on a methodology that combines stress based, continuum damage mechanics (CDM) and fracture mechanics approaches within a unified procedure by using a smeared cracking formulation. The damage model has been implemented as a user-defined material model in ABAQUS FE code within shell elements. Experimental results obtained from previous works were used to validate the damage model. Finite element models were developed in order to investigate the pressure and curvature effects on the impact response of laminated composite shells.     

砌体开裂过程数值模型及其模拟分析

基于损伤力学和脆性理论,将砌体看成是由块体、砂浆、粘结带组成的三相材料,考虑砌体组成材料的非均匀性特点,提出了新的砌体开裂过程数值分析方法,利用材料破裂过程分析系统(MFPA2D),从细观力学层次上数值模拟了砌体试件在水平剪切荷载作用下从损伤到开裂破坏过程,模拟结果与试验结果较为吻合。验证了该数值分析方法的正确性和模型的合理性,同时为砌体开裂破坏预测预报基础理论的研究提供新的分析方法。     

Strength of corroded pipelines

A method of determination of the limiting pressure for gas and oil pipelines susceptible to local corrosion is discussed. The proposed method is based on a combined use of strength criteria of the continuum mechanics and fracture mechanics. Its applicability is verified by the results of numerical studies and laboratory model tests.     

FRACTURE MECHANICS APPLICATIONS TO DRILLING AND BLASTING

Abstract— This paper gives a brief review of research in rock fracture mechanics as conducted at the Fracture and Photo-Mechanics Laboratory (FPML) at Vienna University of Technology. The mechanisms pertaining to percussion drilling and blasting are investigated, with specific reference to the application of fracture mechanics. In order to gain an improved understanding of the mechanisms controlling rock fragmentation, a multidisciplinary approach is followed which includes laboratory experiments conducted in plexiglass and rock, in-situ field experiments and analytical/numerical modelling techniques.
Field experiments revealed that percussively drilled holes exhibit a very shallow region of damaged rock. An analytical model to simulate damage accumulation and crack initiation due to elastic waves generated by impacting drill bits was developed. This model, based on damage and fracture mechanics, was incorporated into a numerical finite difference code. Fracture and damage mechanics parameters are related to the moment tensor which is determined experimentally by means of acoustic emission. Small scale model blasts were used to investigate the blast-induced fractures in the near-borehole zone as well as in the far field. Analytical and numerical investigations give insight into stress wave and gas driven fracturing. The applicability of the dynamic finite difference program SWIFD to the interaction between stress waves and cracks is illustrated.     

Fatigue analysis of post-weld fatigue improvement treatments using a strain-based fracture mechanics model

Untreated and post-weld treated (peened) fatigue details common to welded steel structures are analyzed herein using a strain-based fracture mechanics model. The model is first described and then evaluated by comparison with data from several test-based studies as well as analytical results obtained using two linear elastic fracture mechanics (LEFM) models. The strain-based model is then used to perform several parametric studies. Based on the results of these studies, loading conditions are identified for which ignoring the nonlinear material behaviour may lead to overestimation of the post-weld treatment benefit measured as in increase in the fatigue life of the weld.     

Numerical modeling of elastoplastic deformation and damage accumulation in metals under low-cycle fatigue conditions

A mathematical model that describes the processes of fatigue damage accumulation in structural materials (metals and alloys) under multiaxial disproportionate combined thermomechanical loading is advanced from the standpoint of the damaged medium mechanics. Based on the results of basic experiments performed in a special way, an experimental-theoretical procedure for finding material parameters of the advanced constitutive relations of the damaged medium mechanics is put forward. The advanced version of the constitutive relations of the damaged medium mechanics is shown to adequately (qualitatively and quantitatively) reflect the main effects of elastoplastic deformation and damage accumulation in metals under low-cycle fatigue.     

Modeling delamination growth in composites under fatigue loadings of varying amplitudes

A numerical model was developed to simulate the progressive delamination of a composite subjected to mode I fatigue loading regimes of varying amplitude. The model employs a cohesive zone approach, which combines damage mechanics and fracture mechanics, and requires only standard material data as input, namely the delamination toughness and the fatigue delamination growth curve. The proposed model was validated against delamination growth data obtained from a fatigue test conducted on a DCB specimen. The model predictions agree very well with the experimental results. This model is an initial step toward life prediction of composite structures subjected to complex fatigue regimes.