接触爆炸荷载下金属管道中应力波数值分析

以大口径金属管道为对象,通过数值模拟研究了金属管道在局部外接触爆炸荷载作用下的应力波对其的效应。根据管道应力波传播过程的数值模拟结果,分析了管壁中应力波产生、发展和传播的过程及应力波形特点;比较了管道发生破坏前后应力状态的变化;阐述了管壁各观测点切向、径向与轴向应力随时间的变化特征,并探讨了其中的原因。     

纤维增强复合板中声弹Lamb波的波结构分析

基于线性三维弹性理论和“增量变形力学”理论,采用勒让德正交多项式展开法,推导了在水平和垂直方向施加初应力时,沿纤维增强复合板的非主对称轴方向传播的声弹Lamb波的波动方程,并对波动方程进行数值求解。为了验证方法的准确性,将该文方法求解的各向同性材料的相速度频散曲线与Disperse?软件的计算结果进行比较,两者吻合良好。以单层单向纤维增强复合材料板为例,计算了无初应力状态下的波结构应力曲线,并与应力自由边界初始条件的一致性进行了比较。研究了水平和垂直方向初应力效应对Lamb波频散曲线的影响。针对声弹效应较为敏感的Lamb波A₀模态,着重分析了初应力效应对波结构位移分布曲线的影响。     

纤维束张紧力缠绕复合材料飞轮初应力的三维数值分析

利用平面应力型全弹性模型的思想(即将纤维束张紧力缠绕看成多层复合材料薄环连续过盈装配的过程) , 建立了三维纤维束张紧力缠绕复合材料飞轮初应力分析模型, 并给出了基于面-面接触算法求解张紧力缠绕复合材料飞轮初应力的三维数值方法。算例分析表明, 三维数值分析得到的飞轮的环向初应力及径向初始压应力(数值) 均略低于平面应力模型的结果, 且这种差距随着飞轮轴向长度的增加而缓慢增大; 三维分析证实了平面应力模型关于张紧力缠绕复合材料飞轮的初应力分析有足够的精度。最后给出了三维模型轴向效应的表征方法。      

地应力对混凝土材料中爆炸应力波传播影响规律研究

为研究山体、坝体等自然环境下不同地应力水平对爆炸应力波传播的影响,采用数值模拟技术对不同地应力条件下混凝土试件进行爆炸模拟试验。通过对混凝土试件边界处施加不同大小的应力,观察了在不同地应力下试件承受爆炸荷载后的破坏现象;通过改变模型单边地应力数值设置对照组,随后对不同模型施加相同爆炸荷载,得到了试件中各预设的4个测点的峰值应力及质点运动速度。借助试验中测点峰值应力与质点运动速度等爆炸波特征参数的变化,进而分析了不同地应力大小对爆炸应力波传播的影响。结果表明：地应力对爆炸应力波的影响主要表现为在高地应力水平下的“抑制传播”与低应力水平下的“促进传播”。爆炸过程中,爆炸应力波与地应力的叠加耦合增大了测点峰值应力强度,反之,高地应力抑制了介质颗粒的位移,从而降低了质点运动速度。研究从不同地应力水平对爆炸应力波的传播影响角度入手,创新性地分析了地应力对应力波的抑制作用,其结果可为深地下钻孔爆破过程中破坏区的预判,地下结构抗爆防护等方面提供一定的理论依据。     

考虑应力波的轴心压杆冲击分岔屈曲研究

应力波传播对轴心压杆的冲击屈曲有显著影响,目前的相关研究大多未考虑应力波在杆件远端的反射,且认为轴向应力波在波阵面处为固定约束(波前固定)。该做法忽略了杆件无应力段及远端边界条件对杆件冲击屈曲的影响,从理论上看并不严密。对阶跃荷载作用下不同边界条件轴心压杆的动力分岔屈曲进行了分析,以更为合理的波前连续条件代替波前固定对问题进行了求解,得出了杆件弹性及弹塑性冲击分岔屈曲计算结果,获得了一些有价值的结论。     

应力卸载过程砂岩应力波传播及衰减特性试验研究

由于岩体开挖卸载和原岩应力重新分布的复杂性,围岩体通常处于复杂的应力卸载环境中。为研究应力卸载过程砂岩应力波的传播及衰减特性,设计了长径比L/D≈65的条形试件,利用动静组合加载装置进行了不同轴向卸载应力下的小扰动撞击试验,测得了不同测点处的砂岩应力波信号,研究了不同卸载应力对应力波波形、纵波波速值、波峰的时空衰减规律、波峰及波峰衰减速率等的影响,并建立了经验规律模型。研究表明:砂岩是否具有卸载应力对应力波波形具有显著影响;随应力卸载,纵波波速呈“近似线性+非线性”衰减,波峰及其衰减率均呈指数变化;随距离和时间增加,波峰均呈指数衰减,且不同应力卸载阶段波峰的时空衰减具有不同敏感性;研究结果对爆破开挖条件下深部工程岩体稳定性分析提供了重要的理论参考。     

轴向时变冲击载荷作用下直杆弹性动力屈曲研究

基于应力波理论,用半解析半数值方法对轴向时变冲击载荷作用下的直杆进行研究,给出了一种利用压应力波前附加约束条件求解轴向时变载荷作用下直杆弹性动力屈曲问题的方法。以三角脉冲载荷作用下的直杆为例,对其临界屈曲长度、初始屈曲模态和动力特征参数进行了求解,探讨了脉冲载荷峰值和载荷持续时间对临界屈曲长度和屈曲模态的影响。总结了三角脉冲载荷作用下直杆弹性动力屈曲的规律,并与阶跃载荷作用下的情况进行对比分析,结果与之前文献研究结果吻合良好。     

基于虚拟介质方法数值模拟应力波穿透水舱

将虚拟介质方法推广到应力波与流固界面的相互作用,基于修正虚拟流体方法(MGFM)思想提出一种适用于流固界面应力波折射问题的界面状态计算法则。以此为基础,用Zwas格式和WENO格式分别离散固体和流体控制方程,数值模拟应力波穿透水舱。数值测试表明:虚拟介质方法推广到模拟流固界面上的应力波时,数值误差具有很好的收敛性;该研究提出的计算法则具有一阶精度。一维数值结果与理论解析解能很好地吻合,验证了用虚拟介质方法模拟应力波在流固界面处反射与透射的可行性。应力波穿透水舱的数值结果表明:虚拟介质方法与任意拉格朗日-欧拉(ALE)方法得到的数值结果相近;水舱加压后,透射波的强度也相应的增加;不同的水舱压力下,应力波在流固界面处的折射规律相近。该结论对舰船的防护设计有实际意义。     

泡沫铝衰减一维应力波特性研究

为了解泡沫铝衰减一维应力波特性,完善泡沫铝动力性能的理论体系。首先运用一维应力波理论及泡沫铝的力学特性,对应力波在泡沫铝中的传播规律及泡沫铝衰减应力波性能等问题进行了理论分析。然后基于SHPB(霍普金森压杆)技术,运用LS-DYNA对一维应力波在泡沫铝中的传播规律及泡沫铝衰减应力波特性进行了数值模拟研究。理论与数值模拟结果均表明:在应力波的传播路径上增加泡沫铝,应力波通过泡沫铝后,其应力幅值、波长、及应力幅值作用时间均发生明显的变化;在该条件下,增加5 mm厚的泡沫铝,一维应力波经过泡沫铝后,可以衰减掉未增加泡沫铝时应力幅值的39.9%,应力波由原来的矩形波变成三角形波,波长与持续时间也显著减小。同时,厚度对泡沫铝衰减应力波幅值具有较为明显的影响,相同能量的应力波通过泡沫铝材料厚度越厚,则应力波幅值衰减越明显;由此可知,泡沫铝用于防护冲击与爆炸荷载的缓冲吸能材料方面具有非常好的应用潜力。     

应力波效应对爆炸作用下RC桥损伤特性的影响

为了研究RC桥梁抗爆性能,分析了应力波传播的基本原理,采用AUTODYN软件建立了有限元计算模型,验证了计算方法的有效性,对空中爆炸作用下方形空心RC桥动态响应进行数值仿真,分析了方形截面RC桥应力波的传递路径和不同位置的损伤特点.得到以下结论:爆炸作用下RC桥损伤特性受应力波效应影响明显,且主要为自由面反射引起的拉应力;梁体上缘下表面损伤最为严重,须重点防护;梁体两缘上部形成“耳状”损伤;梁体下缘上表面中部出现明显损伤.     

Influences of initial stresses on guided waves in functionally graded hollow cylinders

Limitations of the manufacturing technology result in the existence of initial stresses in functionally graded material (FGM) structures. In the context of the theory of “Mechanics of Incremental Deformations,” the guided wave characteristics in FGM hollow cylinders under initial stresses in the radial and axial directions are investigated. The Legendre polynomial series method is used to solve the coupled wave equations with variable coefficients. The convergence of the method is discussed through numerical examples. It is found that the influences of initial stresses on the longitudinal waves and on the torsional waves are quite distinct, and that the influences of initial stresses in the axial direction are very different from those in the radial direction, both on the dispersion curves and on the displacement and stress distributions.     

黏弹性正交各向异性空心圆柱中纵向导波的传播

基于线性三维弹性理论和Kelvin-Voigt模型,采用勒让德正交多项式展开法推导了黏弹性正交各向异性空心圆柱中纵向导波的波动方程,数值求解了波动方程并阐述了相关方程的含义。首先计算了大径厚比下黏弹性管的相速度频散曲线和衰减曲线,并与已发表文献的结果进行了对比,验证了程序的正确性,并进一步计算了低阶纵向导波的位移分布和应力分布曲线,验证了方法的可靠性。然后利用方程的解耦特性,分别求解了不同径厚比、不同黏性常数下纵向模态和扭转模态的频散和衰减曲线,研究了径厚比和黏性常数效应对两种模态的影响。最后针对扭转模态导波,研究了材料相关黏弹性常数对其频散特性和衰减特性的影响。      

Comparison Between Using Longitudinal and Shear Waves in Ultrasonic Stress Measurement to Investigate the Effect of Post-Weld Heat-Treatment on Welding Residual Stresses

Fusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (L_CR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when the L_CR method is employed.     

复合管状结构中超声导波的位移分布

对超声纵向导波在复合管状结构中的传播特性进行了分析。然后分析了系统中的位移分布,以此确定了各模式检测管材的最佳频厚积范围和检测的最佳位置。结果表明,各模式的径向和轴向位移在管内壁上的值较大,而在管壁中间和管外壁上的值较小;当频厚积增大到一特定值后,管壁中间和管外壁上的径向和轴向位移都近似为零,此特定值随模式阶次的提高而增加。选取各模式检测的频厚积时,应尽可能的选径向位移较小而轴向位移较大的频厚积点。     

Torsional fatigue with axial constant stress of oligo‐crystalline 316L stainless steel thin wire

A series of symmetric torsional fatigue with axial constant stress tests, a kind of multiaxial fatigue test, was conducted on oligo‐crystalline 316L stainless steel thin wire, which was less than 3.5 grains across diameter of 200 μm. The material presents significant cyclic hardening under symmetric torsion cycling, and hardening is more obvious with the increasing shear strain amplitude. However, symmetric torsional cycle with constant axial stresses tests characterize rapid initial hardening and then gradually softening until fatigue failure. The axial stress has a great effect on torsional fatigue life. Fractography observation shows a mixed failure mode combined torsional fatigue with tensile strain because of axial tensile stress. A newly proposed model with axial stress damage parameter is used to predict the torsional fatigue life with constant axial stress of small scale thin wire.     

正交各向异性空心圆柱体中的纵向导波

基于三维线弹性理论,采用勒让德正交多项式展开法,推导了正交各向异性材料中纵向导波的耦合波动方程,并对耦合波动方程进行了数值求解。首先,为确定方法的适用性和准确性,利用Disperse软件求解各向同性空心圆柱体中纵向导波的频散曲线,并将其与勒让德正交多项式展开法求解结果相对比,二者结果完全一致。然后,讨论了勒让德正交多项式截止值对轴对称导波频散曲线收敛性的影响,并从数值计算的角度分析了产生影响的原因。最后,针对碳纤维缠绕的复合材料空心圆柱体,分别求解纵向、扭转和弯曲三种不同模态纵向导波的相速度频散曲线。计算了不同径厚比下的弯曲模态相速度频散曲线,分析径厚比的变化对频散曲线的影响。     

Guided Waves in Functionally Graded Rods with Rectangular Cross-Section under Initial Stress

The characteristics of the guided waves propagation in functionally graded rods with rectangular cross-section (finite width and height) under initial stress are investigated in this paper based on Biot’s theory of incremental deformation. An extended orthogonal polynomial approach is present to solve the coupled wave equations with variable coefficients. By comparisons with the available results of a rectangular aluminum rod, the validity of the present approach is illustrated. The dispersion curves and displacement profiles of various rectangular functionally graded rods are calculated to reveal the wave characteristics, and the effects of different width to height ratios and initial stress and gradient functions on the guided waves are discussed in detail.     

Kinematics of failure waves in glasses

A new method for observation of the failure waves in glasses is proposed which allows this phenomenon to be reliably and reproducibly monitored, the failure wave propagation velocity to be measured, and an increase in the longitudinal stress to be determined. Using this method, the stresses produced by an elastic shock compression pulse propagating from the entrance of a stack of glass plates to the exit from this stack were experimentally measured. The compression wave exhibits splitting at each interface between adjacent glass plates in the stack, which leads to the formation of transmitted and reflected failure waves and is accompanied by decreasing stress in the leading elastic wave.     

Sub-surface stress measurement of cross welds in a dissimilar welded pressure vessel

Manufacturing process of pressure vessels used in high-temperature applications normally needs employing dissimilar metal welds (DMWs) between austenitic and ferritic steel. However, high amount of thermal stresses at the welds are induced due to differences in coefficient of thermal expansion between the types of steel. This study investigates the evaluation of welding residual stresses in a pressure vessel manufactured by DMW of 316 L stainless steel shell to A106 carbon steel caps as well as similar welding of stainless steel shells. By using longitudinal critically refracted (LCR) ultrasonic waves, the residual stresses are experimentally measured. The ultrasonic method is based on acoustoelasticity law by which the ultrasonic wave velocity could be connected to the material stress. By changing the frequency in which the ultrasonic transducers are working, the LCR waves are able to penetrate in various depths of the material in order to measure the sub-surface residual stresses. Hence, four main aspects are considered in this study: (I) stress evaluation of the DMW; (II) sub-surface stress measurement; (III) stress evaluation of longitudinal weld and (IV) stress measurement in cross weld. It is demonstrated that the residual stresses of the DMW pressure vessel could be comprehensively evaluated by using the LCR method.