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。     

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.     

Comparative assessment of 3D joint marker sets for the biomechanical analysis of occupational tasks

This study involves the comparative assessment of three joint marker sets to estimate joint centres. One set consists of wide elastic bands for marking the joint centres of the ankle, knee, elbow, and wrist joints (band method), a second set uses two spherical markers on either side of the joint (ball method), and a third set defines the location of a local coordinate system from spherical markers placed near the joint (coordinate method). The three marker sets were compared relative to each other. The ball method and the coordinate method were the most similar (average differences ranged from 6 to 16 mm), which is due in part to the common markers in these sets. The band method and the coordinate method were generally the least similar (average differences ranged from 15 to 31 mm). However, the results support the assumption that the marker set consisting of elastic bands can be used as an alternative to other commonly used sets. It may even be better for certain applications because of the relatively small number of missing points. Since the bands encircle the joint they are less likely to be hidden from the view of the cameras than the two marker sets that use balls to mark the joints. Most movements filmed for ergonomic analysis are complex and the incidence of missing points with traditional marker sets is high. Therefore, the band method is a very practical alternative when studying complex occupational tasks.

Relevance to industry

Manual materials handling is a source of industrial injury. Video systems and cinematography are widely used tools to analyze occupational tasks. The use of adequate markers on the subject is essential to have reliable and accurate results for task evaluation.     

Effects of low and high temperatures on tensile behavior of adhesively-bonded GFRP joints

The tensile behavior of adhesively-bonded double-lap joints composed of pultruded glass fiber-reinforced adherends and an epoxy adhesive was investigated under temperatures ranging between −35 °C and 60 °C. The load–elongation response was influenced primarily by the thermomechanical behavior of the adhesive and much less so by that of the adherends. For temperatures above the adhesive glass transition temperature, strength and stiffness decreased with the former being less affected than the latter. The failure mechanism changed with increasing temperature from fiber-tear to adhesive failure. The crack initiation loads were unaffected as long as the temperature remained below the adhesive glass transition temperature. However, the crack propagation rate was higher at low temperatures. Critical strain energy release rates for crack initiation and propagation consistently rose as temperature increased. Modeling results obtained using existing empirical models and FEA compared well to the experimental data in the examined temperature range.     

CFRP Rehabilitation of Concrete Frame Joints with Inadequate Shear and Anchorage Details

The research presented in this study involves full-scale experimental evaluation of carbon fiber-reinforced polymer (CFRP) rehabilitation for existing beam-column joints designed for gravity load with common pre-1970s deficient reinforcement details when subjected to cyclic loading. Numerous studies have demonstrated effectiveness of externally bonded fiber-reinforced polymer (FRP) materials for retrofitting the deteriorating RC structures. Although these materials are widely used in bridges, their applications in buildings have been somewhat limited. In particular, the experimental investigations on external FRP retrofit of deficient beam-column joints have not thoroughly been investigated and they are mainly on scaled-down specimens. The failure of these subassemblies, which possess lack of shear reinforcement within the joint core and shortly embedded positive beam reinforcement, would possibly result in catastrophic collapse of reinforced concrete frame structure during an earthquake event. Recognizing the urgent need to upgrade these structural subassemblies, the current investigation uses CFRP retrofit techniques to enhance the performance of such deficient joints. Experimental variables studied entail the developed CFRP retrofit configurations, and magnitude of the applied column axial load. Comparative analysis of the lateral loads versus drift hysteresis loops, stiffness degradation, and total dissipated energy curves of three as-built and three corresponding CFRP-retrofitted RC joints revealed that significant improvement in the shear capacity of the upgraded joints occurred. More importantly, the slippage of short embedded beam positive reinforcement into the joint was substantially controlled due to the developed CFRP retrofit. The results demonstrate the effectiveness of CFRP retrofit configurations in enhancing the structural performance of actual size connections.     

Damage tolerance investigation of high-performance scarf joints with bondline flaws under various environmental,geometrical and support conditions

The criticality of disbonds on the load-carrying capacity of scarf joints under different environmental conditions was experimentally investigated. Tests were conducted on scarf joints containing bondline flaws of varying lengths and locations under room-temperature (RT), cold-dry (CD) and hot-wet (HW) conditions. The results showed that the residual strength of scarf joints under RT and CD condition decreases exponentially with the size of the bondline flaw up to a threshold length and remains almost unchanged for larger bondline flaws. In contrast, those specimens under HW condition were less sensitive to the presence of disbonds. The effects of scarf angle, adherend composite layup and support condition on the load-carrying capacity of scarf joints with a bondline flaw were also investigated. For specimens where the eccentricity was counteracted by a sandwich support, the residual strength of the joint improved considerably. Fractographic analysis using Micro Computed Tomography and SEM were carried out to examine the effects of the environmental condition on the failure mechanisms of scarf joints.     

Improved fatigue performance for wood-based structural panels using slot and tab construction

This paper presents static and fatigue bending behavior for a wood-based structural panel having a slot and tab (S/T) construction technique. Comparisons were made with similarly fabricated panels without the S/T construction technique. Experimental results showed that both types of panels had similar bending properties in the static tests. However, the panels with S/T construction had better fatigue results. The failure modes were different for the two fabrication techniques. The panels without S/T debonded at the core:face interface. Whereas, the panels with S/T had cracks that propagated within the rib of the core after debonding damage at the core:face interface. The fatigue deflection-life relationship indicated that the S/T construction improved the connection between the faces and core. The S/T construction decreased the deflection growth rate that delayed panel failure. The fatigue stress-life relationship or degradation was better for the panels with S/T construction than the panels without the S/T construction.     

Mechanical properties of fusion welded ceramics in the SiC-ZrB2 and SiC-ZrB2-ZrC systems

Mechanical properties of welded SiC-ZrB₂ and SiC-ZrB₂-ZrC ceramics were measured up to 1700 °C. Commercial powders were hot pressed, machined into coupons, and preheated to 1600 °C before joining the ceramics using either tungsten inert gas welding or plasma arc welding. Toughness of the parent materials was 3–4 MPa*m^1/2 which decreased after welding to 2–2.5 MPa*m^1/2. Strength of the SiC-ZrB₂-ZrC parent material was ~700 MPa at 25 °C, ~300 MPa at 1700 °C, and retained 40–60% of this strength once welded. Strength of the SiC-ZrB₂ parent material was ~600 MPa at 25 °C and 1700 °C and retained 20–30% of this strength once welded. Griffith analysis indicated that the strength in the parent materials was controlled by the size of SiC clusters while strength of welds was controlled by the size of pores in fusion zones. Therefore, removal of pores in produced fusion zones should be investigated to improve strength of future ceramic welds.     

Experimental and analytical study of the structural response of segmental tunnel linings based on an in situ loading test. Part 2: Numerical simulation

The numerical simulation of the in situ test described in the part 1 of the paper is performed by means of two different approaches: a 2D plane stress model and a 3D shell elements model. A consistent modeling of the tunnel behavior is achieved through the proper simulation of the main phenomena involved on the structural response of the lining: (1) the steel fiber reinforced concrete (SFRC) post-cracking behavior, (2) the detailed behavior of the joints between segments and (3) the ground–structure interaction. The origin and the effects of all these phenomena and the modeling techniques employed to simulate them are carefully described and discussed. Finally, the results obtained are compared with the experimental evidences, showing the excellent accuracy achieved in terms of displacements, joints closures and crack patterns.