Key Engineering Materials Vols. 525-526

Abstract: The effect of the interface slip is neglected in most studies on calculating deflection of sandwich beams. By taking a simply supported sandwich beams under uniformly distributed loads as an example, simplified analytical models of the interface slip are established, and corresponding clculation formulas of interface slip between steel panels and concrete and section curvatures are derived. The formula for deflection of sandwich beams are then presented. This formula reflects the relationship of influence each other between the interface slip and deflection.

Abstract: Stiffened plate is widely used in vessel structure because of its high bearing capacity and low weight so the research of failure probability for stiffened plate under explosion load has important engineering meaning. Stiffened plate under near-field explosion is taken as research subject, dynamite density and yield stress of plate are selected as random variables, the original values of one hundred groups of random variables are gotten through the random number generation program, and the moments of random variables are obtained. Based on failure criterion of displacement ductility, the performance function of structure is established, probability density function of performance function is fitted using maximum entropy method then the failure probability of stiffened plate structure is obtained. So as to solve the problem of calculate failure probability when the sample size is small and the probability density function is unknown.

Abstract: Based on the self-focusing property of time-reversal (T-R) concept, a time focusing parameter was suggested to improve the impact source identification method developed in authors previous work. This paper presents a further study on monitoring relatively high energy impact events which caused induced damage on structures. Numerical verifications for a finite isotropic plate and a composite plate under low velocity impacts are performed to demonstrate the versatility of T-R method for impact location detection with induced plastic deformation and delamination damage on metallic and composite structures respectively. The focusing property of T-R concept was adequately utilized to detect impact/damage location. The results show that impact events with various features can be localized using T-R method by introducing the time focusing parameter. It is suited to monitor serious impact events on plate like structures in practice in future.

Abstract: The fatigue test of typical bolt-hole panels with five open holes in a line and the residual strength test of the panels with multiple site crack (MSD) were carried out. The crack initiation life of the test panels and the residual strength of the panels with different MSD crack sizes were obtained by the tests. The application of the net section yield criterion in the determination of residual strength of the panel containing multiple site damage was studied by comparing the calculated results with the test results. The conclusion is that the criterion meets the engineering accuracy requirement in the case of smaller MSD cracked area or smaller MSD crack sizes.

Abstract: In order to understand damage mechanism, the influences of lay-up construction of laminates and environgment on tension behavior of 2D woven composite laminates with an open-hole, which was manufactured by a new technology, uniaxial tension tests are performed in 3 different environments on 4 kinds of lay-up specimens, using a WE-50 electromechanical universal material testing machines. The fracture of specimens are analysed through micrographic observations. The result show that there is a large difference both in tensile strength and damage mechanism due to different kinds of lay-up specimens: 1) the tensile strength of specimens that only with ±45 degree laminated is much lower than other samples with different kinds of layup and its tensile stress-strain curves presents nonlinear; 2)The failure modes and damage mechanism determines the strength of specimens; 3)The change of environment had a certain effect on the mechanical behaviors of materials, in this paper, it will cause the tensile strength of speicmens decreasing.

Abstract: In this paper, to determine the dynamic strength model for steels, a new approach which does not rely on the Hopkinson bar test has been proposed. As the DH36 steel for example, using the results of Taylor impact test and the quasi-static compression test, the initial parameters of Johnson-Cook plastic strength model have been fitted out, then the initial strength parameters have been optimized using the optimization techniques of the sparse Taylor impact cylinder. It has been shown that the optimized results in numerical simulation are consistent with results of Taylor impact test, and the optimized Johnson-Cook model can also well describe flow stress curve fitted from the Hopkinson bar test.

Abstract: The investigation was concentrated on the through-thickness properties of thick-composite laminates, and the development of a novel test method and several specimens with two different shapes and three to four different sizes. The experiments were performed on thick composite specimens; and all through-thickness mechanical properties under compressive and tensile loading with their corresponding failure mechanisms were determined. Overall, the configuration of specimens and test method in this paper are efficient in obtaining the through-thickness properties of thick-composite laminates.

Abstract: After the low-velocity impact test of composite laminates of T800/BA9916, CAI test and compression test of laminates with a hole have been carried out. Two types of models were set up by the finite element software ABAQUS respectively. The FEA results were good agreement with the testing results. The investigation of models with a hole indicates that the appearance time of ultimate compressive load is earlier than that of fiber breakage expanding to boundary. Moreover, the diameter and the depth of blind hole significantly influence the ultimate compressive load.

Abstract: This paper mainly presents a method that can characterize the damage tolerance capability of composite laminates based on the knee-point feature. Based on the experimental study and numerical result, the Knee-point mechanism has been investigated. A new influence coefficient, δ, was introduced, which is applied to calculating the influence of every piles damage to the residual strength of the whole laminates. Finally, a conclusion can be drawn that the damage of 0° piles can represent the damage of the whole laminates, whilst the damage area of 0° piles can be applied to characterizing the damage tolerance capability of composite laminates.

Abstract: This paper proposed a composite damage model including the damage initiation and evolution based on strain to predict the composite intralaminar damage under impact loading. In the numerical simulation, the user material subroutine VUMAT and the cohesive-zone model are chosen to describe the composite damage model and the delamination of interfaces between different plies. ABAQUS software is used to simulate the low-velocity impact of different thickness composite laminates. It is found that the delamination shape and area, the contact force and the deflection of the impactor obtained by the numerically simulation agree well with the experimental results.