THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF STRESS RESPONSE IN ADHESIVE BUTT JOINTS SUBJECTED TO IMPACT BENDING MOMENTS

The stress wave propagation and the stress distribution in adhesive butt joints of T-shaped similar adherends subjected to impact bending moments are calculated using a three-dimensional finite-element method (FEM). An impact bending moment is applied to a joint by dropping a weight. The FEM code employed is DYNA3D. The effects of the Young's modulus of adherends, the adhesive thickness, and the web length of T-shaped adherends on the stress wave propagation at the interfaces are examined. It is found that the highest stress occurs at the interfaces. In the case of T-shaped adherends, it is seen that the maximum principal stress at the interfaces increases as Young's modulus of the adherends increases. In the special case where the web length of T-shaped adherends equals the flange length, the maximum principal stress at the interfaces increases as Young's modulus of the adherends decreases. The maximum principal stress at the interfaces increases as the adherend thickness decreases. The characteristics of the T-shaped adhesive joints subjected to static bending moments are also examined by FEM and compared with those under impact bending moments. Furthermore, strain response of adhesive butt joints was measured using strain gauges. A fairly good agreement is observed between the numerical and the experimental results.     

Generic Debonding Resistance of EB and NSM Plate-to-Concrete Joints

It is well established that adhesively bonding plates to the surfaces of reinforced concrete members is an efficient retrofitting approach. Specifically, two techniques have emerged: Using thin externally bonded (EB) sheets/plates and near-surface mounted (NSM) strips/bars. A good amount of research has been undertaken worldwide to understand the fundamental behavior describing such adhesively bonded plate-to-concrete joints. Unfortunately, until now, no generic model exists to determine the debonding resistance of both retrofitting techniques. In this paper, a generic analytical model is derived to determine the debonding resistance of any adhesively bonded plate-to-concrete joint using an idealized linear-softening local interface bond-slip relationship. The model is derived using a unique definition of the debonding failure plane and confinement ratio such that it is suitable for both the externally bonded and near-surface mounted techniques. The model is validated by comparison with existing push-pull data as well as 14 new push-pull tests with varying plate cross-section aspect ratios. Comparison with an existing well-known model demonstrates the suitability of the proposed generic model. The model can be used to predict the intermediate crack debonding resistance of strengthened reinforced concrete members.     

Performance Evaluation of Precast Posttensioned Concrete Multibeam Deck

An innovative bridge construction utilizing on-site posttensioned precast concrete beams that are compressed together with full depth grouted shear keys and transverse posttensioning is the subject of this paper. In particular, the performance of the shear keys with regard to load transfer and water tightness constitutes the main issues of investigation. This paper presents the results of a live load testing program and associated finite-element analysis results of the as-built bridge. Live truck load test results help provide insights on the lateral (transverse direction) load distribution characteristics among the interconnected beams. The measured lateral distribution of the applied truck load among adjacent beams showed that the load was transferred primarily to the beams close to the truck load position, validating the effectiveness of the shear key details in transporting loads.     

Buckling of a Weakened Column

The buckling problem of a column weakened at an interior location is studied for the first time. The weakness is modeled by a rotationally restrained junction. Exact buckling load values are obtained for the weakened column with various end conditions. Depending on the end conditions of the column, the buckling loads show sensitivity (and insensitivity) to junction location and rotational stiffness. The optimum location of the junction could be at the midpoint, at the ends, or somewhere in between.     

Effect of z-Pins on Fracture in Composite Cocured Double Cantilever Beams

The paper illustrates a new approach to the evaluation of the effect of z-pins on deformations and the strain energy release rate in composite double cantilever beams (DCB) subject to a standard fracture toughness test. The effect of z-pins is modeled by an elastic foundation, based on previously published work. The approach to the solution is based on a separate analysis of the intact and delaminated parts of DCB. The rotational stiffness of the intact part is obtained from the Rayleigh-Ritz solution for this part subjected to a force couple, rather than modeling the rotational restraint by introducing an elastic foundation, as has been done in the previous studies. Subsequently, the deformation of the delaminated part of DCB is analyzed exactly by solving the equation of equilibrium with the appropriate boundary conditions. Based on this solution, the compliance, the rate of change of compliance, and the strain energy of the specimen can be evaluated. The results illustrate the beneficial effect of z-pins on the resistance of DCB to delamination cracking.     

膝关节CT图像处理及其矢量化

定制化人工膝关节置换具有较好的治疗效果,可显著减少病人置换手术后的各种并发症。本文通过对膝关节CT图像处理并提取、矢量化膝关节骨骼轮廓曲线,获得了在CAD软件可利用的轮廓曲线,为膝关节曲面的CAD三维重建及其二次设计铺就了技术路线。     

Investigation on diffusion bonding characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiCp-MMC)

Joining characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiC_p-MMC) were investigated by vacuum diffusion bonding process. The joining performances of the similar and dissimilar composites were studied, and the influences of SiC_p volume percentage and the insert alloy layer on bonding quality and properties of the bonded joints were also estimated. The experimental results indicate that the strength of vacuum diffusion bonded joints decreases with increasing SiC_p volume percentage, and obtaining satisfactory bonding quality in the diffusion bonded joints of the dissimilar Al/SiC_p-MMC is much more difficult than that of the similar Al/SiC_p-MMC. Moreover, the results still manifest that the diffusion bonding either for the similar or for the dissimilar Al/SiC_p-MMC, the suitable insert alloy layer can improve evidently the joining quality of joints, and the strength of diffusion bonded joints corresponding to using the insert alloy layer is apparently higher than that of no insert layer.     

高店水库砌石拱坝的分缝与封拱

论述高店水库砌石双曲薄拱坝的体型设计、分缝方式、缝的布置、坝体内部测温仪器的设置以及大坝封拱时机的选择。     

基于紧支集双正交小波的芯片焊点定位技术研究

芯片封装是保护芯片和增强芯片电热性能的重要工艺,在芯片粘贴在引线框架的贴片基板上后,用金属引线将芯片焊点与引线框架的管脚连接起来实现芯片功能。为了提高芯片引线键合的精度,确保键合机的焊头能够实现准确定位,采用基于紧支集双正交小波的多分辨率分析方法实现芯片和贴片基板边缘的快速检测和特征匹配,实现芯片和引线框架焊点的快速定位。这种方法能够实现芯片图像边缘特征的准确提取、识别和特征匹配。采用紧支集双正交小波进行芯片焊点和引线框架定位时,简化了算法的复杂度,提高了芯片引线框架焊点位置的检测效率和定位精度。