增材制造技术中的弹性各向异性影响因素

Influencing Factors of Elastic Anisotropy for Additive Manufacturing Technology

对弹性材料的各向异性为增材制造技术带来的挑战进行了报道。采用融合了PML全吸收边界的、适用于TTI介质的时域交错网格有限差分法,在弱各项异性的磷灰石(Thomsen参数ε=0.096 4,δ=0.585 0)和强各向异性的锌金属(Thomsen参数ε=0.830 6,δ=2.709 7)中分别开展弹性波传播实验。将对称轴完全/不完全一致的材料薄片拼接为同一大小的正四边形,作为对照组/实验组。在同一位置激发特定参数的点力源,观察波场空间分布与特定位置波形的差异。对照组中的qP波和qSV波均未受到介质分界面的影响,而在实验组中,分界面处发生了不同程度的反射和透射。在实验组,锌金属中传播的波场受分界面的影响相比磷灰石更为明显,且幅度较强的反射波和透射波在介质间不断往返、再生和相互叠加。对实验组和对照组接收波形的qSV波幅度比进行计算,磷灰石为0.465 0,小于锌金属的0.618 8;对介质旋转后和旋转前在同一分量上的qSV波传播速度比进行计算,磷灰石为0.812 3,小于锌金属的0.895 4,暗示着幅度的衰减程度与相邻介质的传播速度差异呈现正相关。各向异性介质的Thomsen参数大小,以及介质在各个方位的传播速度差异程度,是影响弹性波传播特性的两大核心因素,需在增材制造工艺设计中加以重视。

Challenge to the additive manufacturing technology from anisotropy of elastic materialsis reported.TTI medium suited time domain staggered grid Finite Difference Method integratingPML hypersorption boundary is used as a tool for the implementation of elastic wave propagation inapatite with weak anisotropy(Thomsen parameterε=0.0964,δ=0.5850)as well as zinc with stronganisotropy(Thomsen parameterε=0.8306,δ=2.7097).Material slices with completely/incompletelyconsistent symmetrical axis are spliced into the quadrilateral with the same size,taken as the controlgroup/experimental group,respectively.The point force source is excited at the same position,and thedifferences between the spatial distributions of the wavefields and the waveforms of the given positionare observed.In the control group,the qP wave and the qSV wave are not affected by the mediuminterfaces,but in the experimental group,however,the interfaces show various extents of reflectionsand transmissions.In the experimental group,the wavefield propagation in the zinc affected from theinterfaces is more obvious than that in the apatite,and the reflected waves and the transmitted waves withlarge amplitudes constantly hover,regenerate and superpose.Amplitude ratios of experimental group tocontrol group of qSV wave from received waveforms are0.4650for apatite and0.6188for zinc;qSVwave velocity ratios at the same orientation before and after the medium rotation are0.8123for apatiteand0.8954for zinc,indicating the positive correlation of the attenuation extent of amplitude to thepropagation velocity variances of adjacent mediums.Thomsen parameters of an anisotropic medium,aswell as the propagation velocity variances of the medium in all orientations,are two essential factorsaffecting the characteristics of elastic wave propagation,which should be paid close attention to in thedesign of additive manufacturing process.