共查询到17条相似文献,搜索用时 125 毫秒
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采用激光速度干涉仪(VISAR)、X射线衍射(XRD)和扫描电镜(SEM)联合测试技术,利用等厚对称加载和逆向加载实验,研究了Fe MnNi合金的冲击相变和层裂行为。结果发现:加载压力大于6.5 GPa时,Fe MnNi合金样品发生α→ε相变;中心稀疏波的卸载作用使内压力降至4~5 GPa时,Fe MnNi合金样品发生ε→α逆相变,并伴有卸载稀疏冲击波形成。分析Fe MnNi合金样品中塑性波、相变波、稀疏波和稀疏冲击波的传播作用过程,发现加载压力大于其相变应力时,等厚对称加载下Fe MnNi合金存在产生层裂行为的物理机制。 相似文献
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选取合适的材料状态方程和强度模型,通过数值模拟分析超高速撞击下弹丸材料的破碎行为。弹丸的破碎主要有两种:稀疏波引起的层裂和材料在高压作用下的碎裂。由于层裂影响和高压影响下弹丸的破碎方式不同,导致两种情况下材料产生的碎片形状和大小不同。分析球形弹丸在撞击靶板过程中压力脉冲的传播及衰减形式发现:在弹丸和靶板尺寸相同的情况下,弹丸中压力脉冲的脉宽基本保持不变,而峰值压力随着撞击速度的增加而增加;在撞击速度相同的情况下,弹丸中压力脉冲的峰值压力基本不变,而压力脉冲的脉宽随着靶板厚度的增加而增加。弹丸中传播的压力脉冲与后期弹丸背表面的层裂相关,其峰值及变化速率直接影响背表面层裂厚度,其脉宽直接影响背表面沿弹丸径向的层裂深度。得到层裂厚度以及层裂破碎方式的影响区域,对研究后期碎片云分布有重要参考价值。 相似文献
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脉冲激光引起金属靶板层裂的阈值条件 总被引:5,自引:1,他引:4
本文考虑单脉冲激光作用于金属靶引起的应力波单次反射导致层裂的阈值条件,包括激光通量与应力波强度的定标关系、应力波传播时的衰减、入射波与反射波相互作用以及不同层裂判据的比较。本文结果指出,对于一定的激光通量和靶板厚度,只有一定范围内的激光脉宽才能造成层裂,最低激光通量则对应于最佳激光脉宽。本文的方法和结论也适合于飞片撞击造成的层裂现象。 相似文献
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基于单孔洞近似,对不同撞击速度下高纯铝的部分层裂实验进行了数值模拟研究,讨论了微孔洞长大对波传播的影响及其在自由面速度波剖面上的表现. 通过分析微孔洞周围的应力场变化,认识到实测自由面速度波剖面出现"回跳"特征并不能说明材料发生完全层裂,其直接原因是样品内部微孔洞长大所引起的局部卸载效应. 将计算得到的自由面速度波剖面和微孔洞相对体积与实验结果进行了对比分析,发现两者均符合很好,表明采用单孔洞增长来近似描述部分层裂样品中随机损伤发展及其对波传播的影响是可行的.
关键词:
层裂
孔洞增长
自由面速度波剖面
微孔洞相对体积 相似文献
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采用VISAR和X光联合测试技术,利用等厚对称和逆向碰撞法测量了FeMnNi合金高压加卸载历程和相变层裂信息。加载过程中,FeMnNi合金样品发生α→ε相转变,相变波速大于塑性波速,在撞击面上相变波与塑性波合并成单一相变波;卸载过程中,FeMnNi合金样品可能发生了逆相变,形成了除合并相变波在自由面反射中心稀疏波R以外的两道卸载波S1和S2。等厚对称高压加载下,FeMnNi合金样品发生了二次层裂。分析中心稀疏波R、卸载波S1和S2在样品中的传播作用过程,发现样品发生冲击相变和卸载逆转变是导致其等厚对称高压加载下发生二次层裂行为的主要原因。 相似文献
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层错四面体是一种典型的三维空位型缺陷,广泛存在于受辐照后的面心立方金属材料中,对材料的力学性能有显著的影响.目前,关于层错四面体对辐照材料层裂行为的影响还缺乏深入系统的研究.本文使用分子动力学方法模拟了含有层错四面体的单晶铜在不同冲击速度下的层裂行为,对整个冲击过程中的自由表面速度及微结构演化等进行了深入的分析.研究发现,层错四面体在冲击波作用下会发生坍塌,并进一步诱导材料产生位错、层错等缺陷.在中低速度加载下,层错四面体坍塌引起的缺陷快速向周围扩展,为孔洞提供了更宽的形核区域,促进了孔洞的异质成核,造成材料层裂强度大幅度减小.当冲击速度较高时,层错四面体坍塌导致的局部缺陷对材料的层裂强度不再有明显影响. 相似文献
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强激光辐照下纯铝的力学响应和层裂的实验测量与分析 总被引:3,自引:2,他引:1
采用速度干涉(VISAR)测试技术,对强激光辐照下纯铝的动态力学响应和层裂特性进行了实验测量和分析。样品厚度分别为200 μm 和485 μm,激光脉冲的半高宽约为10 ns,功率密度变化范围为1010~1011 W·cm-2。实测了样品自由面速度波形,反映了强激光加载作用下材料损伤演化过程以及损伤对材料动态响应的影响。计算得到了冲击波强度(2.0~13.4 GPa) 和不同拉伸应变率下铝的层裂强度(1.6~2.3 GPa)。在所采用的实验条件和1维近似下,激光辐照产生的冲击波强度与激光功率密度之间成线性关系。最后讨论了层裂强度与拉伸应变率之间的关系,显示层裂强度随着拉伸应变率的增加而增大。 相似文献
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The mechanisms of photomechanical spallation are investigated in a large-scale MD simulation of laser interaction with a molecular target performed in an irradiation regime of inertial stress confinement. The relaxation of laser-induced thermoelastic stresses is found to be responsible for the nucleation, growth, and coalescence of voids in a broad sub-surface region of the irradiated target. The depth of the region subjected to void evolution is defined by the competition between the evolving tensile stresses and thermal softening of the material due to the laser heating. The initial void volume distribution obtained in the simulation of laser spallation can be well described by a power law. A similar volume distribution is obtained in a series of simulations of uniaxial expansion of the same molecular system performed at a strain rate and temperature realized in the irradiated target. Spatial and time evolution of the laser-induced pressure predicted in the MD simulation of laser spallation is related to the results of an integration of a thermoelastic wave equation. The scope of applicability of the continuum calculations is discussed. PACS 79.20.Ds; 61.80.Az; 02.70.Ns; 83.60.Uv 相似文献
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Thermoelastic wave induced by pulsed laser heating 总被引:6,自引:0,他引:6
In this work, a generalized solution for the thermoelastic plane wave in a semi-infinite solid induced by pulsed laser heating
is developed. The solution takes into account the non-Fourier effect in heat conduction and the coupling effect between temperature
and strain rate, which play significant roles in ultrashort pulsed laser heating. Based on this solution, calculations are
conducted to study stress waves induced by nano-, pico-, and femtosecond laser pulses. It is found that with the same maximum
surface temperature increase, a shorter pulsed laser induces a much stronger stress wave. The non-Fourier effect causes a
higher surface temperature increase, but a weaker stress wave. Also, for the first time, it is found that a second stress
wave is formed and propagates with the same speed as the thermal wave. The surface displacement accompanying thermal expansion
shows a substantial time delay to the femtosecond laser pulse. On the contrary, surface displacement and heating occur simultaneously
in nano- and picosecond laser heating. In femtosecond laser heating, results show that the coupling effect strongly attenuates
the stress wave and extends the duration of the stress wave. This may explain the minimal damage in ultrashort laser materials
processing.
Received: 23 May 2000 / Accepted: 26 May 2000 / Published online: 20 September 2000 相似文献
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Laser gas-assisted material processing finds wide application in industry. The modelling of heating, elastic response of the substrate material, and the wave analysis gives insight into the laser workpiece interaction. In the present study, laser gas-assisted heating of steel is considered. The normal component of the thermal stress is taken as the source of load for the flexural wave generation in the material. The flexural wave generated is simulated and the wave characteristics are analyzed at four locations at the workpiece surface. The numerical scheme employing a control volume approach is introduced when solving the governing equations of flow and heat transfer while finite element and spectran element methods are used when solving the stress and wave equations. It is found that the normal component of the stress is tensile. The dispersion effect of the workpiece material, interference of the reflected beam, and partial overlapping of second mode of the travelling wave enable to identify a unique pattern in the travelling wave in the substrate. 相似文献
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Laser pulse heating of metallic surfaces results in rapid rise of temperature in the region irradiated by the laser beam. This in turn results in high temperature gradient in this region. The irradiated substrate material expands as a response to the temperature gradient. Consequently, high thermal stress levels are developed in the region of the high temperature gradient. In the present study, closed form solutions for temperature and stress fields due to a laser pulse decaying exponentially in time are presented. A Laplace transformation method is employed in the analysis. The resulting equations are non-dimensionalized with the appropriate parameters. It is found that temperature rises rapidly during the early heating period in the surface region. In this case, internal energy gain dominates the conduction losses from the surface vicinity. The thermal stress levels attain high values in the surface region. The stress wave developed is compressive and it propagates with a wave speed c1 inside the substrate. 相似文献
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提出了一种锥形靶层裂实验新方法,开展非一维应变冲击条件下高纯铜初始层裂行为实验研究,讨论了锥形靶内部损伤分布特征及其与自由面速度典型特征之间的内禀关系.结果显示:1)初始层裂的锥形靶内部出现了连续损伤区,损伤区扩展方向与锥面平行,从锥底到锥顶呈现了不同的损伤状态,从微孔洞独立长大到局部聚集,最后形成宏观裂纹,这种损伤状态分布特征归因于锥形靶内部拉伸应力幅值和持续时间的空间演化;2)通过锥形靶横截面损伤度定量统计分析,揭示损伤演化早期的微孔洞成核与早期长大过程是随机的,而损伤演化后期的微孔洞聚集过程具有显著的局域化特征;3)不同位置处实测的自由面法向粒子速度剖面呈现出典型的层裂Pull-back信号,但是通过与内部损伤分布特征对比,揭示基于Pull-back速度获得高纯铜层裂强度本质是微孔洞成核阈值应力,Pull-back回跳速度斜率反映了损伤演化速率,Pull-back回跳幅值与损伤度引起的应力松弛密切相关. 相似文献