激光辐照下充内压柱壳动态爆裂的数值模拟

采用动力有限元显式积分程序,对承受内压、在侧面受到激光辐照的圆柱壳的热 力学响应进行了数值模拟,展现了圆柱壳热软化、鼓包和爆裂的动态失效过程。获得的柱壳失效方式与实验现象基本吻合;还给出了不同内压作用下柱壳的破坏时间,获得一些定性的认识。     

激光辐照诱导的热与力学效应

对激光辐照诱导的热与力学问题研究进展进行了综述,包括材料在高温、高升温速率下的本构关系,典型薄板和柱壳等结构在激光辐照下的热力破坏效应,多层材料体系的激光破坏行为等几个方面,并着重介绍了包含相变与烧蚀过程的激光破坏分析模型与机制研究,激光辐照效应的流–热–固耦合数值模拟方法,以及短脉冲激光引起的冲击与破坏机理等方面的研究新进展。     

Progress in thermal-mechantical effects induced by laser

对激光辐照诱导的热与力学问题研究进展进行了综述,包括材料在高温、高升温速率下的本构关系,典型薄板和柱壳等结构在激光辐照下的热力破坏效应,多层材料体系的激光破坏行为等几个方面,并着重介绍了包含相变与烧蚀过程的激光破坏分析模型与机制研究,激光辐照效应的流-热-固耦合数值模拟方法,以及短脉冲激光引起的冲击与破坏机理等方面的研究新进展.     

激光辐照诱导的热与力学效应

对激光辐照诱导的热与力学问题研究进展进行了综述,包括材料在高温、高升温速率下的本构关系,典型薄板和柱壳等结构在激光辐照下的热力破坏效应,多层材料体系的激光破坏行为等几个方面,并着重介绍了包含相变与烧蚀过程的激光破坏分析模型与机制研究,激光辐照效应的流–热–固耦合数值模拟方法,以及短脉冲激光引起的冲击与破坏机理等方面的研究新进展.     

激光辐照下圆柱壳结构的稳定性分析

针对航天工程中常用的承受轴压作用的薄壁圆柱壳,分别采用解析方法与特征值屈曲有限元方法分析了圆柱壳结构在均匀轴压作用下的稳定性能,得到了屈曲承载力.并进行了对比,验证了有限元模型的合理性.采用线性屈曲特征值有限元方法分析了强激光辐照作用下圆柱壳的稳定性能,分析表明激光辐照导致壳体局部温度上升并由此带来材料参数的改变,是因为激光辐照在壳体中引起了热应力与热应变,使轴压圆柱壳的屈曲承载力明显降低.论文还着重对加筋圆柱壳结构的稳定性进行了研究,数值分析结果表明,加筋能有效提高圆柱壳结构的抗压承载力,激光辐照作用下,加筋对轴压作用下圆柱壳的屈曲承载力的提高作用更为明显.     

激光辐照下预内压低碳钢圆柱壳爆裂断口分析

通过实验揭示了预内压低碳钢薄柱壳在激光辐照下裂纹萌生、扩展和止裂过程的较完整物理图象。对断口特性进行了深入分析，发现辐照区上裂纹的形成和扩展机制以韧性为主，断口在柱壳壁厚度方向有明显分层，如外层为塑性变形层，内层是韧窝或层状撕裂，部分试件的最内层出现脆性石头状断口。给出了激光辐照区应力分布与裂纹萌生之间的关系，同时探讨了激光辐照区材料金相组织变化对材料细观损伤和初始裂纹萌生的影响，有助于进一步对激光辐照下柱壳的断裂问题进行更深入的理论研究。     

充内压圆柱壳在激光辐照下的初始裂纹萌生机制研究

通过高速摄影在实验中观测到充压柱壳上初始裂纹萌生于激光辐照区中心．通过数值模拟、断口分析和激光辐照区材料的金相分析等手段揭示了裂纹初始萌生的物理力学机制，并进一步证实了裂纹初始萌生位置的问题．根据研究结果，确定了影响裂纹起始萌生的力学量．本项目工作的完成有助于激光辐照下充压柱壳断裂问题的深入研究．     

内爆炸载荷下圆管变形、损伤和破坏规律的研究

以物理统计和唯象研究相结合的方法,建立了微孔洞型的损伤函数模型和损伤演化方程,以变形热力学,Ｄｒｕｃｋｅｒ公设和内变量理论为基础建立了含损伤热塑性材料的增量型本构关系,用所建立的本构关系及损伤演化方程对内部爆轰作用下的圆管破坏过程完成了系列数值模拟,数值结果与实验结果相比较,在圆管变形过程,破坏时间,破坏速度,破坏应变,破坏应变率等信息方面都是基本一致的。     

离散元与壳体有限元结合的多尺度方法及其应用

在深入研究复杂结构和非均质材料冲击响应和破坏机理的过程中,往往遇到多尺度计算问题。本文尝试建立三维离散元与壳体有限元结合的多尺度方法用于处理圆柱壳问题,该方法采用三维离散元对感兴趣的局域进行局部模拟,利用平板壳体有限元进行整体模拟,采用一种特殊的过渡层使离散元区和有限元区能很好的衔接。我们将这一方法应用于激光辐照下充压柱壳的热/力耦合冲击破坏响应,得到的模拟结果与文献报道有较好的吻合。     

电活性聚合物球壳的力电不稳定性

应用连续介质力学有限变形理论,分析了不可压电活性聚合物球壳在外加电场及内压作用下发生非对称变形的力电不稳定性问题。文中给出了不同外加电场下球壳的变形曲线和应力分布曲线, 结果表明对壁厚小于临界壁厚值的薄壁球壳,当内压大于临界内压值时,球壳可以产生不稳定的非对称变形。文中求得了球壳发生不稳定变形的临界壁厚及临界内压,探讨了外加电场对两个临界值的影响规律,同时讨论了外加电场对球壳中应力分布的影响。     

变温下橡胶材料力学性能的实验分析

利用Zwick020材料试验机研究了天然橡胶材料在不同温度条件下单向拉伸的大变形力学行为。得到了不同温度和不同加载速率条件下材料的应力-应变关系曲线和材料的破坏条件,由此分析了高温和低温的温度变化条件及加载速率对材料力学性能的影响,得出天然橡胶材料在大变形条件下的温度和加载速率敏感特性。同时利用实验结果拟合出材料的应变能函数,并应用热超弹性模型对材料进行了理论分析。结果表明,理论分析结果与实验结果仅在一定温度范围内吻合得较好,因为材料软化或硬化,在很高或很低的温度情况下二者有一定差别。     

Fracture properties of metals under rapid heating and loading

The phenomenon of the fracture of metals under rapid heating and loading has been studied. An impactpendulum testing technique combined with laser heating was developed. The energy absorbed to fracture the specimens, the surface temperature, the deformation and the impact force were measured. Experimental results give evidence of a high-temperature transition in fracture properties. A microscopic-investigation technique was developed using high-speed cameras to observe the propagation of the fracture-metal grain-level cracks which were identified as liquation cracks. The properties of these cracks are related to the observed fracture mechanism.     

低功率密度激光辐照结构的热动力失效

研究了低功率密度激光辐照结构的热动力失效。考虑材料的高温软化特性，研讨了温升速率对材料和结构的影响、结构热软化后的宏观受力和变形的重新分布以及可能的热运动。给出了几种热动力失效的结构破坏实验结果。     

激光冲击喷丸与激光辐照LY12铝合金材料拉伸力学行为的实验研究

为了研究激光冲击喷丸与激光辐照处理后LY12铝合金材料的微尺度变形特点和失效机理,对经过不同激光功率密度处理后的LY12铝合金材料,在扫描电镜下进行了原位拉伸力学行为和失效机理研究。在扫描电子显微镜（SEM）下,得到各组试件的拉伸载荷曲线和不同载荷下的微观区域图像,并利用数字图像相关技术进行不同载荷下的微观区域全场变形分析,并对拉伸断口形貌也进行了分析。研究表明：激光处理的功率大小对LY12铝合金拉伸最大载荷有明显的影响,激光处理的交界处有较强的应变集中。     

Feasibility study on strengthening heating effect of high power short pulse laser on biological tissue by micro/nano metal particles

A new method for enhancing the heating effect of high power short pulse laser on biological tissue by micro/nano metal particles was proposed. Theoretical analysis of the influences of the micro/nano particle kind, the concentration and the microcosmic distribution of micro/nano particles on the temperature response was carried out with a multi-layer hyperbolic heat conduction model with volumetric heat generation. The results indicate that embedding micro/nano particles could improve the surface temperature increase of biological tissue with short duration and reduce the deeper material temperature under the same heating condition, which would help strengthen the heating effects of high power short pulse laser on biological tissue. This study may open a new technical approach for improving laser applications.     

泡沫铝夹芯双方管结构准静态轴压性能的实验研究

对几种泡沫铝夹芯方管结构的准静态轴压性能进行了实验研究。结果表明,较空管及泡沫铝夹芯单管结构,泡沫铝夹芯双管结构的承载能力及能量吸收效率明显得到增强。双管夹芯结构中外管撕裂模式的结构行程利用率和能量吸收效率高于相应的外管周期折叠模式。而泡沫铝四角填充方式提高了双管夹芯结构相同变形模式下的能量吸收效率和结构变形的稳定性。同时研究了内管管壁及材料强度对泡沫铝夹芯双管结构的影响。随着内管壁厚增大,双管夹芯结构的能量吸收效率提高,而内管材料强度影响不明显。     

An extended strain energy density failure criterion by differentiating volumetric and distortional deformation

We extend Sih’s strain energy density criterion (Sih, 1974) for crack kinks and material failure by weighting differently the volumetric and distortional parts in the extended strain energy density factor. The work is inspired by the factor that failure by microscopic shearing governed by distortion and microscopic separation controlled by hydrostatic tension represent distinct deformation processes, and should be treated differently as we count their influences to material failure. With the weight parameter introduced to the extended strain energy density factor criterion, we explain satisfactorily several critical experiments which reported crack kink in samples subjected to mixed-mode loading. The extended strain energy density idea is also used to derive a generalized pressure-dependent yielding criterion, which supplies a theoretical basis for those novel strength criteria for materials like bulk metallic glasses. Corresponding methods to determine the two material parameters, the critical strain energy density factor and the weight parameter quantifying the relative contribution by distortion over volumetric deformation, are discussed.     

Influence of stretch and temperature on the energy density of dielectric elastomer generators

Application of dielectric elastomers(DE) has remarkably increased in mechatronics because they are suitable candidates for energy harvesting due to their low cost,light weight, and high energy density. The dielectric elastomer generators(DEGs) exhibit high performance regardless of the applications scale. However, functioning as a generator, a DE may lose its efficiency due to several failure modes including material rupture, loss of tension(LT), electrical breakdown(EB), and electromechanical instability(EMI). The failure modes confine the area of allowable states for generation process.Dielectric constant and dielectric strength of such elastomers depend on the amount of applied deformation and also working temperature, which are often ignored in theoretical simulations. In this paper, variations of the above-mentioned parameters are considered in mechanical and electrical modellings to investigate their effects on energy density and efficiency of generators. Obtained results show that, ignoring the variations of material dielectric constant and dielectric strength leads to overestimation of the specific energy.Furthermore, it is shown that, for an acrylic-based generator, the specific energy sharply decreases with temperature rise.     

重组竹顺纹冲击力学性能研究

重组竹是一种新型竹基复合材料,其力学性能优于落叶松等木材。为评价重组竹在动态加载下的顺纹抗冲击力学性能,以密度1.06 g/cm3、含水率8.52%、龄期3～5年的毛竹基重组竹为研究对象,通过准静态单轴压缩和循环加卸载以及动态加载实验,研究了重组竹加载变形过程、各项力学性能指标以及对应变率的敏感性。结果表明:重组竹顺纹压缩过程可以分为弹性变形和弹塑性变形阶段,破坏类型为延性破坏,其各项强度指标随应变率的提高而提高,动态增长因子与应变率之间呈现线性关系,斜率为0.0024;重组竹压缩过程中的应变比能与应变之间呈线性关系,且随应变率的增长而增大,证明其吸能能力随着应变率的增大而提高。实验结果证明,重组竹顺纹具有良好的抗冲击力学性能和显著的应变率效应。