FAILURE-MODE TRANSITION SPEED IN THREE-DIMENSIONAL TRANSIENT DEFORMATIONS OF A MICROPOROUS HEAT-CONDUCTING THERMOELASTOVISCOPLASTIC PRENOTCHED PLATE

ABSTRACT

We analyze three-dimensional finite coupled thermomechanical deformations of a rectangular plate with two parallel notches placed symmetrically about the horizontal centroidal plane of the plate. The edge surface of the plate between the two notches is struck by a cylindrical projectile of diameter equal to the distance between the notches and made of the same material as the plate. The plate material is modeled as heat-conducting, microporous, elastoviscoplastic, and isotropic. Both the brittle and the ductile failures initiate at points adjoining the notch-tip surface that are on the midplane of the plate and propagate toward the outer surfaces. Even for a relatively thin plate, the difference in the times of initiation of failures on the mid and front surfaces is significant. Also the two failure modes on the mid surface initiate much later than that predicted by the plane strain analysis. Thus an experimentalist observing fracture on the front or the back face of the plate will see it initiate much later than the times given by the plane strain analysis of the problem. For a steel plate, it is found that the failure mode transitions from brittle to ductile at an impact speed of about 21.8 m/s.     

大型风力机圆形扩展基础倾覆破坏机理分析

为研究以坡积土为持力层的风电基础在风荷载作用下的倾覆破坏机理,以2 MW装机容量的圆形扩展基础为研究对象,基于ABAQUS有限元软件对该基础的室内1∶10缩尺模型的地基土应力和基础沉降进行计算研究。同时利用该基础的缩尺模型试验结果验证数值模型的可靠性。研究表明:随机风荷载引起的地基土应力的扩大效应和不均匀沉降的扩大效应,是导致风力机基础出现倾覆破坏的主要原因;当受强风荷载作用时,迎风侧基础边缘的土体首先进入塑性区,发生屈服破坏,导致上覆土体隆起,基础倾覆破坏就会随之发生。建议在进行风电基础设计计算时,对风力机基础中轴线上的相对沉降验算点处的沉降乘以合适的沉降扩大系数,以保证基础结构安全稳定。     

Surface elasticity-based modeling of rotating functionally graded nanoshafts in thermal environments

Thermoelastic field analysis of a rotating functionally graded nanoshaft (RFGNS) in thermal environments is of interest. The governing equations of the rotating nanoshaft with varying material properties along the radial direction are obtained. Two nonclassical boundary conditions, namely, fixed-free and free–free, are established accounting for the surface energy effect. Using finite element method and Hamilton's principle, the thermoelastic field within RFGNS is evaluated. The effects of power-law index, aspect ratio, temperature, angular velocity of the RFGNS, and surface energy on the displacements and stresses are displayed in detail.