Applied Mechanics and Materials Vols. 157-158

Abstract: The present work deals with the finite element modelling of low velocity impact response of different types of composite panels for body armour application. The response of these composites panels including bonded, unbonded and partially bonded laminates has been simulated using non-linear finite element package LS-DYNA. 2D shell elements in LS-DYNA have been used to represent both resin bonded glass fabric targets and dry woven glass fabric panels. The hemispherical shaped projectile is being modelled with 3D solid elements. The results of the numerical analysis showed that the value of contact force for the fully bonded composites panels was significantly higher than that observed for the panels consisting of dry woven glass fabric. However, the corresponding displacement was substantially lower. The similar simulation of the partially bonded composite panels has shown a reduction of both the contact force and the displacement. In addition, it has been shown that the partially bonded composite panels are capable of absorbing higher levels of energy than the rigid panels.

Abstract: A compact feeding network for a wideband circularly polarized multi-mode Global Navigation Satellite System (GNSS) antenna is presented. Four feed method for the antenna is adopted to suppress the higher modes and increase the 3dB axial ratio (AR) bandwidth. A broadband phase shifter with 0°, 90°, 180°, 270° phase differences using composite right/left-handed transmission line structure combined with novel schiffman phase shifter is analyzed, designed, simulated, implemented and measured in this article.

Abstract: A composite cellular beam may offer much advantage by using its web openings, but it could lose some fire resistance capacity. The paper studies the influence of HVAC ducts to composite cellular beam while the ducts’ weight is supported by the web holes.

Abstract: Precast construction is prevailing from China to America and Europe for its advantage in shortening construction schedule, mitigating environment pollution and reducing life cycle costs. Precast segmental bridge columns are a new structural system, whose widespread to high seismicity is slow due to concern of their seismic response. Carbon fibre reinforcement is a new material with high strength and well corrosion protection. The purpose of this contribution is to explore the applicable of carbon fibre reinforcement in reducing seismic damage and enhancing the lateral bearing capacity in precast concrete columns. The effect of partial steel reinforcement energy dissipation bars being replaced with carbon fibre bars in precast segmental bridge columns was investigated. The simulation model was proved valid by comparison with pseudo static test results. Then parametric study of amount of carbon fibre on the force-displacement curve, damping ratio, energy dissipation and joint opening was conducted. The results show the carbon fibre reinforcement is applicable in precast segmental bridge columns with competitive response behavior over its mild reinforcement counterpart.

Abstract: In order to improve the accuracy of the computational translation, an effective tool---the cross entropy was proposed. After the analysis of the reasons of the low accuracy, the information entropy was introduced into the disambiguation. The practice of ambiguity elimination shows the method has high accuracy and this study provides an effective way to improve the computational translation.

Abstract: Considering that most of the research on vibratory stress relief (VSR) is excited by low-frequency vibration at present, high-frequency-exciting VSR on small Cr12MoV quenched specimens was studied. A high-frequency vibration table system was adopted as the exciter of the VSR. To increase the vibration level, a novel vibration level amplifying device was put forward. High-frequency VSR on the same group of small Cr12MoV quenched specimens was carried out under various vibration levels. The residual stress before and after vibration was comparatively analyzed. The results showed that the high-frequency vibration had the better effect on eliminating and homogenizing the residual stress and that increasing the vibration level of high-frequency-exciting could improve the effect of high-frequency VSR.

Abstract: Fretting fatigue cracks always initial at the tralling of contact region, because the stresses in the vicinity of the contact zone exhibit steep gradients. A fracture mechanics approach is usually used to estimate fretting fatigue propagation life. In this paper, extended finite element method combined with fracture mechanics is used to study fretting crack propagation behaviors. The computation results reveal that fretting crack nucleation is mainly decided by fretting, and the cycle bulk stress is the main reason for crack propagation. Also the X-FEM exhibits merits in fretting fatigue problem.

Abstract: This paper presents a mass-spring model applied in the manipulation of elastic deformable object for home service robot application. In this paper, we present a system used to fold a piece of rectangular cloth from a specific initial condition using robot. The cloth is modeled as a 3D object in a 2D quadrangular mesh based on a mass-spring system and its state is estimated using an explicit integration scheme that computes the particle position as a function of internal and external forces acting on the elastic deformable object. The state of the elastic deformable object under robot manipulation is currently tracked from the trajectory of the mass points in the mass-spring system model in a self developed simulator, which integrates a mass-spring model and a 5 DOF articulated robotic arm. To test the reliability of the model, the simulator is used to predict the best possible paths for the robotic arm to fold a rectangular cloth in two. In the test, the state of the object is derived from the model and then compared with practical experiment. Based on the test, the error is generally acceptable. Thus, this model can be used as an estimator for vision-based tracking on the state of an elastic deformable object for manipulation by home service robots.

Abstract: Terrorist bombing attacks will endanger and may even destroy the target building structures, resulting in economic loss and casualties. Typical columns and floor slab systems are not designed to resist the complex blast loading. So, in recent years, the effects of blast on conventional public buildings are focused on. In this paper,a two-bay,one-story reinforced concrete frame structure which is used to model a portion of a typical reinforced concrete frame structural system is used to investigate the blast response. The experiments are conducted on two models, allowing a variation in explosives standoff and explosives charge. In each experiment,the blast pressure values are recorded and the degree of damage of the frames are studied. According to the two kinds of experiments, two numerical models are established. ALE method which considers the interaction of the explosive, the air, and the structure is applied.Structure response analyses are performed using the large deformation finite-element computer code, LS-DYNA. The numerical results are compared with the experiment results, and a good agreement is obtained. The calculating results also demonstrate that some experimental value is unreasonable.

Abstract: Due to constant exposure to high torque and loads toughness, compressive durability and light weight of joint parts are crucial factors for biped walking humanoid robot parts. When polymer transmission parts are used for the manufacture of humanoid robot joint, wear becomes an important factor in terms of transmission error (backlash) between the input and output axes, ex. between the motor and the robot’s leg joint. In such joint system, a polymer bushes is directly connected to a cam plate, playing an important role in the robot's movement ability. In this work, the influence of wear of reinforced poly-ether-ether-ketone (PEEK) polymer bushes in friction against 7075 aluminium alloy cam plates is investigated in order to establish the application possibilities in transmission parts in humanoid robot’s joint. The PEEK bush surface conditions as well as the input axis-output axis backlash require close examination, so that efficient systems can be built. Sliding wear tests were performed on bushes under 0-50kgfcm loaded torque while the cam plate oscillated. Based on the wear observation, it was found that in a high load range the backlash increased along with number of cycles due to PEEK bush wear. The bush surface roughness also increased during testing. Roughness of PEEK bush surface and the loaded torque for output axis were significantly related to backlash of output axis in robot joint.