MACROMECHANICAL/MICROMECHANICAL CHARACTERIZATION OF WELDS IN ALUMINUM BY COMBINED EXPERIMENTAL/NUMERICAL APPROACHES

ABSTRACT In this paper, elastic moduli of both the base metal and weld zone are estimated for aluminum welds by combined experimental/numerical approaches based on vibration testing, static testing and Finite Element (FE) methods. The general approach used is to indirectly determine the elastic properties by combining either experimental modal vibration analysis data or static 3-point bend test data with the corresponding finite element analytical model. Two types of welded joints, Al 6061 arc welded and Al 6111 spot friction welded (SFW) lap joints were considered. Modal vibration characteristics obtained from the experiments were compared with the corresponding FE model results at the macromechanical level, and the weld zone modulus was indirectly determined so as to give the best agreement between predicted and measured modal frequencies. The results indicate a modulus reduction of 15 % to 45 % for the weld zone depending on whether it is two sided or one side arc welded sample, and whether only the first mode or several modes are used, but results are inconclusive for the SFW samples due to uncertainty about modeling of weld zone material and/or geometric properties

Static and fatigue performance of resin injected bolts for a slip and fatigue resistant connection in FRP bridge engineering

This paper presents test results to evaluate the slip and fatigue performance of Resin Injected Bolted Joints (RIBJs) for pultruded Fibre Reinforced Polymer (FRP) material. The objective of the test series is to provide a robust method of connection for structural engineering that is both fatigue and slip resistant. Forty-six joints (using 23 specimens) were subjected to either static or combined static/cyclic loading at ambient room temperature. Ten specimens (five batches of two) had bolted connections without injected resin and were included to provide baseline static joint strengths. Sikadur®-30 and RenGel®-SW404 were the two cold-curing epoxy based resins used to fabricate the 13 RIBJ specimens. Testing was conducted with double lap-shear joints in accordance with modified guidance from Annex G and Annex K in standard BS EN 1090-2:2008. The specimen’s geometry was established using this British Standard and an American Society of Civil Engineers pre-standard for pultruded thin-walled structures. Rectangular plates for the lap joints were cut from either a wide flange section of size 254×254×9.53 mm or a flat sheet of 6.35 mm thickness. Bolting was with either M16 or M20 steel threaded bolts of Grade 8.8. Sixteen specimens, for eight batches of two specimens were failed in a short duration for static strength. Four RIBJ specimens had static load cycling to an assumed service load level. Three specimens out of 23 were subjected to staged static and cyclic fatigue loadings to determine stiffness changes, life-time ‘slip’ load and residual joint strength. The reported results are evaluated for slip and fatigue performance and the main finding is that resin injection shows much promise as a mechanical method of connection in pultruded FRP structures

Damage behavior of potting materials in sandwich composites with pinned joints

The damage behavior of the potting materials around a pinhole, being used in the mechanical joints of sandwich composites, is investigated experimentally. The sandwich composite panels used in the tests were manufactured by the vacuum-assisted resin infusion technique. Each of the top and bottom face sheets of the panels consisted of two woven E-glass/epoxy layers. As the core material, PVC foam (AIREX (R) C70.55) was used. The potting material consists of an epoxy resin and hardener system mixed with short E-glass fibers (4 wt%). The diameter of the potting material D and the edge distance to the center of pinhole E were considered as the two main varied dimensions. They were chosen as D = 10, 12, 15, and 18 mm and E = 15, 20, and 25 mm. The damage mechanisms of the potting material and sandwich sections are presented by using load-displacement variations and images of the damaged samples, subjected to in-plane pin loading

A review of numerical analysis of friction stir welding

Friction stir welding is a relatively new solid-state joining technique which is widely adopted in different industry fields to join different metallic alloys that are hard to weld by conventional fusion welding. Friction stir welding is a highly complex process comprising several highly coupled physical phenomena. The complex geometry of some kinds of joints and their three dimensional nature make it difficult to develop an overall system of governing equations for theoretical analyzing the behavior of the friction stir welded joints. The experiments are often time consuming and costly. To overcome these problems, numerical analysis has frequently been used since the 2000s. This paper reviews the latest developments in the numerical analysis of friction stir welding processes, microstructures of friction stir welded joints and the properties of friction stir welded structures. Some important numerical issues such as materials flow modeling, meshing procedure and failure criteria are discussed. Numerical analysis of friction stir welding will allow many different welding processes to be simulated in order to understand the effects of changes in different system parameters before physical testing, which would be time-consuming or prohibitively expensive in practice. The main methods used in numerical analysis of friction stir welding are discussed and illustrated with brief case studies. In addition, several important key problems and issues remain to be addressed about the numerical analysis of friction stir welding and opportunities for further research are identified

Failure loads of mechanical fastened pinned and bolted composite joints with two serial holes

An experimental and numerical study has been carried out to investigate the first failure load and the bearing strength behavior of pinned joints of glass fiber reinforced woven epoxy composite prepregs with two serial holes subjected to traction forces by two serial rigid pins. In the experiments, a number of parameters such as the edge distance-to- upper hole diameter (E/D), the distance between center of two holes-to-hole diameter (K/D), and the width of the specimen-to-hole diameter (W/D) were varied. Each specimen configuration was analyzed using the finite element model. Generally, comparison between computed and experimental results for first failure load presented a good agreement. Also to see the effects of preload moments and sea water on the bearing strength of joints an experimental investigation was carried out. For this purpose, the specimens were tested under 3 and 6 Nm preload moments for unimmersed condition. Other specimens held in sea water for 24 h. Afterwards, the same experiments were performed to the immersed specimens. It was observed that the immersion of test specimens into sea water causes a decrease in the failure load without a preload moment. The test specimens under preload moments produce nearly the same bearing strength as unimmersed specimens. (C) 2010 Elsevier Ltd. All rights reserved