利用W-Cu梯度层连接93W合金与无氧铜的实验研究

针对“面向等离子体元件”对W—Cu复合材料的需求,进行了利用W—Cu梯度层连接93W合金与无氧铜的实验研究。首先选用Zn作为烧结助剂,采用粉末冶金方法热压烧结了不同W含量的W-Cu梯度层,研究了烧结温度、W含量对其致密度和微观结构的影响,确定了适宜的烧结条件为温度1123K,压力20MPa,保温时间60min。在该条件下制备的W-Cu梯度层的致密度大于96％,其物相为W、Cu,二者以机械混合形式共存。在此基础上,通过在93W合金与无氧铜之间加入三层W含量逐渐变化、无宏观界面的W—Cu梯度层,在梯度层致密烧结的同时,实现93W合金与无氧铜的连接。     

揭博高速公路典型顺层边坡破坏机理分析及防治对策研究

揭博高速公路分布较多的顺层路堑边坡。本文以K220+045~+257右侧路堑顺层边坡为例,采用地质调绘、病害调查和理论分析等等方法对顺层滑坡的病害情况及其发育规律进行分析,并提出相应的防治对策,为顺层路堑边坡病害治理提供了可借鉴的工程经验。     

岩石爆破层裂机理的研究

基于连续介质损伤力学，从Ｎａｊａｒ各向同性脆性损伤的能量定义出发，从能量角度分析了爆炸应力波传播过程中岩石损伤程度的变化，确定了岩石发生层裂的判据，即当入射压缩波尚未反射部分与反射拉伸波叠加后出现的拉应力等于岩石的损伤抗拉强度（本文简称）时，岩石发生层裂。从而弥补了岩石爆破层裂理论的不足，完善了岩石爆破机理。     

岩石爆破层裂机理的研究

基于连续介质损伤力学,从Ｎａｊａｒ各向同性脆性损伤的能量定义出发,从能量角度分析了爆炸应力波传播过程中岩石损伤程度的变化,确定了岩石发生层裂的判据,即当入射压缩波尚未反射部分与反射拉伸波叠加后出现的拉应力等于岩石的损伤抗拉强度（本文简称）时,岩石发生层裂。从而弥补了岩石爆破层裂理论的不足,完善了岩石爆破机理。     

外廊式RC框架破坏机理的振动台试验研究

通过地震现场调查,对汶川地震中大量倒塌的外廊式钢筋混凝土框架结构的破坏特点、倒塌方向及堆积情况进行了总结。设计相似比为1/4的两层外廊式框架结构模型,并进行了振动台框架倒塌试验。试验再现了典型外廊式框架的倒塌过程。根据框架倒塌模式及试验结果分析,研究了各层加速度反应随结构破坏程度加深的关系及层间位移角变化规律。总结出框架结构破坏不同阶段所对应的层间位移角限值,计算了不同输入下各柱的动轴压力大小,分析了外廊式框架的破坏机理及倒塌原因。研究结果表明：在倾覆弯矩引起的动轴压力作用下,外廊式框架单柱侧的总轴压比升高,延性显著降低,柱端塑性铰区出现压剪破坏是引起外廊式框架倒塌的主要原因。     

增塑型超韧尼龙11的力学性能和增塑机理

增塑后尼龙１１的冲击强度及断裂伸长率大幅提高,但断裂强度并未大幅降低。尼龙１１的增塑机理是,增塑剂破坏了尼龙１１的分子间氢键作用。研究表明,增塑型超韧尼龙１１的断裂面具有独特的形态,这是一种首次发现的新型断裂现象。本文首次将上述现象归结为“多重裂延”机理。     

多层隔热材料对填充式结构高速撞击损伤影响的实验研究

在填充式结构中加入多层隔热材料(MLI),利用二级轻气炮发射铝球弹丸在真空环境下对其进行高速撞击实验,获得了MLI位于不同位置时的防护结构损伤模式,研究MLI对填充式结构高速撞击损伤与防护特性的影响。结果表明:当MLI位于首层薄铝板前侧时,薄铝板穿孔尺寸增大,首层薄铝板耗散弹丸撞击动能的能力增强,有助于填充式结构高速撞击防护性能提高;当MLI位于首层薄铝板后侧时,弹丸击穿薄铝板后次生碎片云团的膨胀扩散受到抑制,不利于填充式结构高速撞击防护性能提高;在相同撞击条件下,当MLI位于填充层前侧时,填充层中心穿孔尺寸增大,当MLI位于舱壁前侧时,舱壁弹坑分布范围减小。     

蜂窝纸板压缩破坏机理研究

从蜂窝纸板的结构和力学角度分析了蜂窝纸板的破坏模式、纸蜂窝芯的压缩破坏过程和蜂窝胞壁壁板受载破坏机理,得知蜂窝纸板的压缩破坏主要与纸蜂窝芯的结构和蜂窝胞壁的屈曲有关,为蜂窝纸板缓冲性能的研究提供了理论基础.     

石灰岩在爆炸载荷作用下的破坏机理试验研究

为了探讨岩石在爆炸载荷下的力学特性和破坏机理,采用耦合填塞装药、耦合无填塞装药和不耦合填塞结构模拟了爆炸应力波和爆生气体的不同加载强度,在石灰岩中进行模拟爆破试验,对爆炸应变波及其参数、以及爆破后岩石内部的声波速度进行了测试.基于模拟爆破试验结果,对石灰岩的力学特性和爆破损伤程度进行了分析,得到了岩石在不同爆破条件下的爆破损伤和破坏规律.     

氮化铝与无氧铜低温界面热阻的实验研究

用低温真空实验装置稳态导热法,实验研究了界面温度和接触压力对氮化铝(AIN)与无氧铜(OFHC-Cu)问接触界面热阻的影响.在实验温度(90～210 K)和压力(0.273～0.985 MPa)范围内,A1N/OFHC-Cu界面热阻随接触压力的提高而降低,而当界面温度上升时界面热阻由于热载子热运动的强化而降低,温度较高时,界面热阻随压力变化的速率较大.     

Effect of stress parameters on ratcheting deformation stages of polycrystalline OFHC copper

Engineering stress‐controlled ratcheting tests under different sets of stress amplitudes and mean stresses show that ratcheting deformation in polycrystalline OFHC copper occurs in three different stages. A plateau region with almost no accumulation of inelastic strain follows general ratcheting deformation during initial loading cycles. With breakdown of the plateau region inelastic ratcheting deformation occurs at an increasingly rapid rate. The effect of the stress amplitude on the ratcheting process is found to be more than mean stress effect. Reconstruction of the ratcheting curves clearly separates the conditions for stress‐controlled low cycle fatigue with zero mean stress and ratcheting with tensile mean stress.     

Thermonuclear fusion under high-velocity cluster impact

Numerical investigations have been carried out for thermonuclear fusion processes under hypervelocity impact of micro-projectile composed of deuterium-tritium mixture on a surface of solid target. The results are discussed. Crucial thermonuclear fusion initiation parameters are defined.     

Determination of inelastic heat fraction of OFHC copper through dynamic compression

An approach to determine the inelastic heat fraction (IHF) value of metal by high-speed compression is established by combining dynamic deformation, infrared (IR) photography and finite element simulation. OFHC copper specimens are dynamically compressed and infrared thermographs captured at a rate of 1000 images/s. FEM simulation of the deformation is undertaken and the initial IHF value input adjusted until the computed average surface temperature matches the experimental data. It is found that for the IHF value identified, the predicted surface temperature distribution also exhibits good correlation with experimental results. For final strains in the range of 44–60%, a consistent IHF value of 0.68 is obtained. Using this value, the surface temperature of a sample deformed to a different final strain and at a different strain rate is predicted by FEM simulation and the numerical results show good agreement with test data in terms of average surface temperature and surface temperature distribution. The temperature field for the entire specimen is also predicted. Results indicate that high-speed compression at a strain rate of 1000/s to a final engineering strain of 70% may result in initiation of dynamic recovery in OFHC copper.     

Destruction of organic glass under high-velocity impact

The results are given of experimental investigations of the interaction between a 2.5-g polyethylene impactor and a massive target of organic glass. The impact velocity ranges from 1 to 3.2 km/s. A statistical analysis is made of masses and sizes of fragments of the impact and spallation craters of the target.     

Grain-boundary structure of oxygen-free high-conductivity (OFHC) copper subjected to severe plastic deformation and annealing

The influence of grain-boundary structure on grain growth in copper subjected to severe plastic deformation has been studied using orientation imaging microscopy. The investigation was carried out on oxygen-free high-conductivity (OFHC) copper which was wire drawn to a true strain of about 4 and processed by equal-channel angular extrusion (ECAE) to 4 and 8 passes via “route B_c” (where the billet is rotated by 90° in the same direction between consecutive passes). The grain-boundary character distribution (GBCD) of the as-drawn wire was similar to that of ECAE-processed specimens, and both materials possessed a higher fraction of high-angle grain boundaries (HAGBs) than special coincidence-site lattice (CSL) boundaries. While the high fraction of HAGBs was retained in the annealed wires, they were transformed to CSL boundaries in the annealed ECAE-processed materials. In spite of an initially smaller grain size, when annealed at 750 °C for 1 h, the grain size of the 4-pass ECAE-processed material was larger than that of the wire drawn to a similar strain. This difference was attributed to a high density of high-mobility 35–50° 0 0 1 boundaries in the 4-pass ECAE materials. On the other hand, the presence of 50–60° 1 1 1  pinning boundaries in the annealed 8-pass material accounted for the smaller grain size after recrystallization.     

Vortex structures in a ceramic under high-velocity impact

A finite-element method in a two-dimensional axisymmetric formulation is used to analyze the characteristics of shock-wave processes in a ceramic plate under the impact of a high-speed cylinder. It is established that a vortex structure is formed and the evolution of the vortices is investigated. Pis’ma Zh. Tekh. Fiz. 23, 86–90 (December 26, 1997)     

Numerical modelling of foam-cored sandwich plates under high-velocity impact

This paper studies the high-velocity impact response of sandwich plates, with E-glass fibre/polyester face-sheets and foam core, using finite-element models developed in ABAQUS/explicit code. The failure of the face-sheets was predicted by implementing Hou failure criteria and a procedure to degrade material properties in a user subroutine (VUMAT). The foam core was modelled as a crushable foam material. The numerical models were validated with experimental data obtained from scientific literature. The contribution of the foam core on the impact behaviour was evaluated by the analysis of the residual velocity, ballistic limit, and damaged area.     

Experimental study of CFRP fluid-filled tubes subjected to high-velocity impact

In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a phenomenon that occurs when a high-energy object penetrates a fluid-filled container, are of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. For the present work, water-filled CFRP square tubes were subjected to an impact of steel spherical projectiles (12.5 mm diameter) at impact velocities of 600–900 m/s. The CFRP tubes were filled to different volumes to examine how volume might influence the tank behavior. The composite test boxes were instrumented with six strain gauges and two pressure transducers, and the formation process of the cavity was recorded using a high-speed camera. The damage produced in the tubes was then analyzed, and differences were found according to the testing conditions. This work presents the results of these tests.     

Experimental analysis of fluid-filled aluminium tubes subjected to high-velocity impact

Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure increasing the risk of catastrophic failure and excessive structural damage. It is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. For the present work, water-filled aluminium square tubes (6063-T5) were subjected to impact by steel spherical projectiles (12.5 mm diameter) at impact velocities of 600–900 m/s. The aluminium tubes were filled at different volumes to study how an air layer inside the tank might influence the impact behaviour. The test boxes were instrumented with five strain gauges and two pressure transducers. The formation process of the cavity was recorded with a high-speed camera. This work presents the results of these tests.     

Experimental investigation on constitutive behavior of PVB under impact loading

During automotive related accidents, PVB plays an important role in both pedestrian and passenger protection as an interlayer of automotive windshield. In this paper, dynamic constitutive behavior of PVB material is thoroughly studied. Firstly, a set of dynamic compression impact experiments on PVB specimens using SHPB (Split Hopkinson Pressure Bar) method are conducted at strain rates from 700/s to 4500/s. Details of the constitutive response is analyzed based on the validation of experiment data. Stress-strain curve of PVB is then divided into two parts, i.e., “Compaction Stage” and “Hardening Stage”. Dislocations and entanglements among molecules are major reasons for the two-stage phenomena. Constitutive behaviors are different in low and high speed impacts, leading to three times more energy absorption ability of PVB in high speed impact scenario. Further, data fitting models based on both Mooney–Rivlin and Ogden Model are studied and then compared. Mooney–Rivlin Model is found to be more appropriate to describe PVB material. Moreover, PVB is proved to be a rate-dependent material with the failure strength intensify factor β ≈ 4. PVB material shows little viscoelasticity after comparison of the both models with and without the viscoelasticity part. Results offer critical experimental data, constitutive models and analysis of PVB material to further study of automotive crashworthiness and pedestrian/passenger protection.