Numerical and experimental investigations of laser shock forming aluminum alloy sheet with mold

Laser shock forming (LSF) technology employs shock waves to form sheet metal into three-dimensional complex parts, and has application potential in manufacturing sheet metal parts. In this paper, the forming of 2024 aluminum alloy sheet with LSF was investigated through numerical and experimental methods. The numerical model was established with the commercial code ABAQUS/Explicit. The formed conical cup was obtained from the simulation, and validated by the experiment. With the verified numerical model, the deformation behaviors, including deformation velocity, sheet thickness variation and strain distribution, were studied. In addition, the influence of different shock wave pressures on the forming precision was also investigated. The experimental and numerical results show that the metal sheet loaded by shock wave can take the shape of the mold, and the non-uniform thickness is distributed in the formed cup. The investigations also display that there exists reverse deformation at the central region of deforming sheet owing to severe collision during LSF. In order to obtain formed part with better quality, an appropriate pressure of applied shock waves is required.     

Deformation and fracture behaviour of plate specimens subjected to underwater explosion—a review

Behaviour of plate specimens subjected to underwater explosion is of interest to metal forming community and ship designers. The break down of the original molecule of an explosive into product molecules associated with the evolution of large amount of heat generates a shock front in the water medium, followed by a gas bubble pulsation. The interaction of the shock wave with a plate imparts energy to it, which is dissipated in the form of deformation. The intensity of explosion determines whether a plate undergoes elastic deformation, yielding, plastic deformation or fracture. When the deformation is in the elastic range, the stress developed in the plate is given as a function of the material and shock wave parameters. As the intensity of explosion progressively increases, the elastic to plastic transition occurs over a specific shock factor. Plastic deformation is predicted as a function of geometric and material properties of the plate and shock pulse impulse. Deflection-time history reveals the reloading effects of the shock wave. As the deforming plate absorbs maximum energy, depending on its strength and ductility, it undergoes fracture. Terminal strain to fracture is considered as the criterion for explosive shock performance of ship materials.     

岩石中爆炸冲击波能量分布规律初探

本文就冲击波能量主要消耗在爆腔扩胀,形成裂隙和引起岩石弹性变形上讨论。首先分析了冲击波作用岩石变形和破坏的特点,在此基础上探讨了炮孔柱状装药爆破时冲击波能量的分布规律以及各部分能量消耗量的求算方法。     

Analytical and experimental evaluation of energies during shock wave loading

Analytical expressions were developed using gas dynamic equations to evaluate the energy associated with the incident shock wave (incident energy) and the reflected shock wave (remaining energy) for a shock tube experiment. The real time deformation profile of the specimen being loaded by a shock tube was also used to calculate the deformation energy. A shock wave loading on a homogeneous aluminum panel in a simple shock tube experiment was used to illustrate the implementation of these methods.     

Finite Element Evaluation of Acoustic Energy Penetration of Partially Submerged Tube Bundles

In this paper, the finite element software ANSYS is used to model ultrasonic waves propagating through a liquid volume containing partially submerged tubes. An immersible transducer is used to generate the waves. The goal of the investigation is to find an appropriate excitation frequency in order to perform ultrasonic cleaning of the tubes. Modal analysis of the coupled tubes–liquid system is conducted to evaluate the dynamic behavior of the tube structures under ultrasonic wave excitations. The frequency at which the acoustic waves efficiently penetrate the tube array with least energy loss and least deformation to tube structures is obtained, and will be used to probe the capability and the potential of utilizing ultrasonic energy as a non-destructive technique for cleaning tube bundles.     

Weak shock waves and shear bands in thermoelastic solids

The linear weak shock wave (acoustic wave) propagation and the existence of shear bands are examined in finitely deformed thermoelastic solids within the framework of the theory of singular surfaces. The jumps of certain field variables across the shock wave front are obtained by using Taylor series expansions of them. The propagation condition of shock waves in a thermoelastic solid is obtained by using the strain–energy function corresponding to Duhamel–Neumann expression. The propagation speeds of weak shock waves are determined for a particular state of deformation, that is, general dilation. The formation of shear bands and the magnitudes of critical stretches are obtained for the deformation states of uniaxial, biaxial extension and for uniform dilation.     

Uni-axial strain loading of a rubber rod by planar shock waves

Summary The uni-axial strain loading of a rubber rod struk head-on by a planar shock wave is studied experimentally and numerically. A physical model capable of describing the rubber response to its collision with the incident shock wave is proposed. This model takes into account the rubber compressibility and the friction forces developed in the contact surface between the rubber and its surrounding rigid walls. The good agreement that exists between experiments and their numerical simulations verifies the validity of the proposed physical model and the accuracy of the numerical scheme used for the numerical simulations. It is found that for the considered loading mode, i.e., uni-axial strain loading, no shock waves exists in the rubber rod. The stresses measured/calculated in the rod result from compression wave motion (with constant velocity) in it. It is also found that the friction developed between the rubber rod and its bordering rigid walls plays an important role in damping the intensity of the wave propagating in the rubber due to its collision with the incident shock wave. The larger is the friction, the larger is the stress damping rate in the rubber.     

Self-ignition of hydrogen-air mixtures behind reflected explosive waves

Experimental results are given, which reveal the special features of selfignition of hydrogen-air gas mixtures behind reflected explosive pressure waves at moderate (below 1200 K) temperature and elevated pressure. The experiments are performed in a modified shock tube which provides for generation of explosive pressure waves. The explosive waves are characterized by a jump of parameters of shock-compressed gas (pressure, temperature) at the front with their subsequent continuous decrease. This is how undesirable gas-dynamic effects are attenuated, which are due to hypothetical pre-explosion preheating of combustible mixture by compression waves. As previously, the experiments involving standard shock waves (with constant pressure/temperature levels) revealed a significant (by a factor often and more) deviation of measured values of delay of selfignition from the calculated values towards decreasing.     

激光冲击2024 铝合金诱导动态应力应变实验研究

为了研究激光冲击波动态加载过程中金属材料的动态应力应变特性,采用高功率激光器单次冲击2024 铝合金薄板,利     

The propagation and reflection of finite amplitude cylindrically symmetric shear waves in a hyperelastic incompressible solid

Summary We consider axially symmetric shear waves propagating in an incompressible hyperelastic thick-walled cylindrical shell, whose strain energy function is expressible as a truncated power series in terms of the basic strain invariants. A continuous pulse is initiated at the interior boundary of the cylinder by surface tractions of finite duration. The pulse propagates away from the interior boundary, then reflects from the outer boundary, and subsequently reflects back and forth between the two boundaries of the cylinder. We analyze shock development of the first incident and first reflected wave. The incident pulse can break before it reaches the outer boundary. Using Whitham's nonlinearization technique, we determine conditions under which the incident wave breaks and which shock waves can subsequently occur. Similar calculations are carried out for the first reflection. The formulas obtained for the incident pulse provide accurate estimates of the breaking distance and time, and the location of the shock paths, for any incident shock waves that occur. Results obtained for the reflected wave cannot be used to make similar estimates, but they do reveal that once the pulse has completely left the outer boundary, the possible shock that can occur is the same as for the incident wave. Our analysis is carried out for axial shear waves. A similar analysis can be done for torsional shear waves, but not for combined axial and torsional shear wave propagation. We illustrate the conclusions of our shock analysis with numerical solutions obtained using a relaxation scheme for systems of conservation laws. Numerical results are obtained for axial shear and for combined axial and torsional shear. These results indicate that the shock behavior indicated by our analysis of axial shear is also valid for combined axial and torsional shear wave propagation.     

Simulation of liquid infiltration and semi-solid extrusion for composite tubes by quasi-coupling thermal-mechanical finite element method

As a new metal forming technology, the liquid infiltration and semi-solid extrusion process can produce various composite parts, such as tubes, bars, and shaped products, in a single process. In this paper, the liquid infiltration and semi-solid extrusion process for forming a composite tube is simulated by means of thermal rigid-plastic quasi-coupling FEM method. The key technologies such as the handling of liquid phase zone, the transition between liquid and solid phase zones, the grid re-meshing method and the establishment of the boundary condition have also been studied. Based on the FEM simulation software developed by the authors and the grid re-meshing technology, the distribution of stress field, strain field and deformation force in the liquid infiltration and semi-solid extrusion process for forming composite tubes are obtained. The deformation force simulation results accord with the experimental data, indicating the reliability of the system. Therefore, the present research is theoretically valuable in the product quality control and the process parameter choice.     

激波与障碍物作用加速衰减的数值研究

强激波在管道内传播时与障碍物作用会发生绕射和反射,同时还会生成膨胀波等复杂波系结构。初步研究表明,若障碍物形状合适,则可导致激波强度衰减,但其衰减程度与障碍物形状的关系则仍待进一步研究。该文利用高阶数值格式结合沉浸边界法(IBM)以及自适应网格加密(AMR)技术,对激波在管道内与不同迎风面角度的障碍物作用过程进行了数值模拟,对激波与障碍物作用衰减的机理进行了分析,并对三种障碍物对激波衰减的效果进行了对比分析,结果表明,迎风面斜率为负的障碍物相对于其他两种障碍物具有最佳激波衰减效果。另外,与目前隧道中常用的壁面为矩形障碍物的模型为算例进行了对比,结果表明,该三角形模型比矩形障碍物具有更显著的激波衰减效果。     

多排钢管冲击波压扁行为研究

多排钢管吸能元件在冲击波作用下的大变形问题，对于抗爆结构的吸能装置设计具有重要意义。在单个钢管的动力压扁过程清楚的基础上，根据实验分析了多排钢管受径向冲击塑性行为，建立了八塑性铰机构，描述了钢管压扁位移速度场。给出了塑性铰附近的塑性弯矩值计算方法。     

金属热成形过程的综合数值模拟

金属在热成形过程中的微观组织演变是影响产品力学性能的关键因素,该演变过程取决于温度、应变和应变速率。本文基于有限变形理论和微观组织演变的数学模型,建立了能够模拟变形过程、温度变化过程和微观组织演变过程的有限元法,研制了通用的三维有限元计算软件,并在H型钢三维热轧模拟方面进行了深入开发,给出了原材料为C-Mn钢的H型钢热轧过程综合模拟结果。综合对比了8组不同工艺下的热轧实验结果和计算机模拟结果,二者均吻合良好,表明本文方法能够较好地预报金属热成形过程。     

One-dimensional expansion waves in gasdynamic shock tubes

Summary One-dimensional expansion waves in 4 different shock tube driver geometries are investigated and compared. These are the plane wave in a straight tube and its reflection from a co-planar wall, the cylindrical wave in a wedge shaped duct and the spherical wave in a cone. Characteristics and pressure histories are computed for all cases. Pressure measurements in truncated cones are presented to check the predicted pressure histories for the spherical wave.     

激光多普勒效应在爆炸冲击测量中的应用研究

将激光多普勒效应应用于爆炸圆筒实验中,实现了圆筒表面形变过程的动态测量.系统采用了外差式纵向激光多普勒测量结构,利用1/2波片、1/4波片与偏振分光棱镜相结合及外差式参考光结构,有效地提高了多普勒信号的强度与信噪比.在信号处理方面,采用了短时傅里叶的频谱分析方法,提高了系统噪声适应能力和信号处理速度;另外采用了相位差频谱校正技术,实现了频率细化和精度提高.最后给出了在不同爆炸载荷条件下的圆筒实验测量结果.     

存在衰减和真实气体效应的激波管激波速度的计算

用一般理论计算激波管参数,由于激波的衰减不可避免以及一定压力下的气体是非理想气体,故会有不小误差。本分别考虑了衰减和真实气体效应这两种对激波速度有影响的因素,对一种具有良好压力平台的激波管（驱动气体为Ｈ２,被驱动气体为ＣＯ２）中的激波速度进行了计算。首先采用考虑真实气体效应的理论,计算破膜后形成的初始激波速度;在激波沿管运行理论不能准确计算的阶段,采用由实验得出的激波衰减公式进行计算。计算结果与     

利用振荡管双开口结构消弱反射激波的研究

气波制冷机由于振荡管结构原因,造成激波运动到管末端产生具有一定强度的反射激波,而反射激波的存在是制约制冷效率的一个重要因素,因此,消除反射激波成为气波制冷技术研究的一个重要方向.本文分析了振荡管内激波的行为及反射激波对制冷效应的影响;对现有的几种消弱反射激波技术进行了对比及评价,在此基础上,提出了一种新的消弱反射激波的方法-采用振荡管双开口结构.实验证明,这种方法可有效消除反射激波,使制冷效率平均提高10%以上,而且大大优化了整机的结构,体积仅为原来的十分之一左右.     

SHOCK COMPRESSION PROCESSING OF POWDERS

Shock compression processing is emerging as a novel technique for fabrication of esoteric materials. Not only can metal and ceramic powders be dynamically consolidated, but both equilibrium and non-equilibrium structures can be synthesized under the high pressure regime during the passage of shock waves of sufficient magnitude and duration. The shock waves can be generated by impact from a plate (accelerated by compressed gas or detonation of explosive) or direct contact with explosives. Very hard metallic and ceramic powders, as well as those powders that cannot be processed by conventional powder processing techniques can be easily compacted to solid densities. The bonding mechanisms in shock compaction involve the rapid and intense deposition of shock energy, preferentially at interparticle regions, resulting in extensive plastic deformation. This may lead to interparticle welding due to partial melting or simply solid-state diffusional bonding.

Shock compression processing technology will be reviewed with emphasis on the processing aspects. Specific examples of shock compaction of RSP alloys and ceramics will be presented, and feasibility of commercialization of the technique will be discussed.     

Rubber tubes in the sea

A long tube with elastic walls containing water is immersed in the sea aligned in the direction of wave travel. The waves generate bulges that propagate at a speed determined by the distensibility of the tube. If the bulge speed is close to the phase velocity of the waves, there is a resonant transfer of energy from the sea wave to the bulge. At the end of the tube, useful energy can be extracted. This paper sets out the theory of bulge tubes in the sea, and describes some experiments on the model scale and practical problems. The potential of a full-scale device is assessed.