Deformation Behavior Of Joints Research Articles

Microstructure and deformation behavior of rapid cooling friction stir welded Q&P1180 steel joint

In this work, Q&P1180 steels were butt welded by friction stir welded (FSW) and rapid cooling FSW (RCFSW), aiming to investigate the influence of rapid cooling on the microstructure and deformation behavior of joints. The results showed that for FSW and RCFSW joints, stir zone (SZ) composed of martensite phase, and inter-critical heat affected zone (ICHAZ) composed of ferrite/martensite dual-phase microstructure, and subcritical heat affected zone (SCHAZ) consisted of ferrite, martensite, carbide and residual austenite phases. Compared with FSW joint, the grain of HAZ was refined, the contents of residual austenite and ferrite increased, while the content of cementite decreased in RCFSW joint. The tensile strength and elongation of FSW joint were 1292 MPa and 7.5 %, respectively. Compared to FSW joint, the tensile strength of RCFSW joint slightly decreased (1237 MPa), while the elongation greatly increased to 13.5 %. During tensile deformation, the strain was mainly concentrated in HAZ of FSW joint, while the strain transferred from HAZ to basal material (BM) of RCFSW joints, and finally fractured in BM.

Effect of deformation rate on the axial joint strength made of Fe-SMA

Iron-based shape memory alloys (Fe-SMA) have been applied to structural members, such as pipelines and curved pipes, for underground structures due to their excellent properties. However, in the case of an earthquake or high winds, the resulting impact force causes a bending and twisting behavior in joints of the pipe. For this reason, a clear understanding of the relation between the deformation rate and joint strength is strongly needed. In this work, the specimen of a joint which a round bar made of SUS304 is tightened by a hollow cylinder made of Fe-SMA was prepared by first expanding the cylinder at a constant quasi-static rate and heating it up to the austenitization temperature. Then, a push-out test, which a compressive-shear combined force acts, was conducted at various deformation rate including the impact level to evaluate the axial joint strength. The results scientifically demonstrate that the axial strength would show the negative sensitivity with respect to deformation rate. However, when the deformation rate exceeds 8.3 mm/s, positive rate sensitivity can be found. This work may provide us with a systematic understanding of the deformation behavior of joints made of Fe-SMA and the safety design of the product.

Comparison of drop performance between the Sn37Pb and the Sn3.8Ag0.7Cu solder joints subjected to drop test

This study was concerned with the drop performance between the Sn37Pb and the Sn3.8Ag0.7Cu (wt. %) solder joints when the specimens were subjected to drop test after soldering process. The U-notch butt-jointed specimen was adopted and a lab-designed drop tester was employed. Meanwhile, the electrical resistance values of two kinds of solder joints were measured and recorded after certain drop tests, and finally drop number versus resistance curves were plotted and compared. From the resistance variation with the drop number, it was observed that the Sn37Pb joints presented significantly higher drop performance than the Sn3.8Ag0.7Cu ones. For the Sn3.8Ag0.7Cu specimens, the average drop number before failure was approximately 15-18 and then the resistance values sharply increased. However, the average drop number of the Sn37Pb joints was over 110 and the increasing rate of the electrical resistance was smooth, which is consistent with the results of the board-level drop test. Moreover, one specimen of each kind was picked out and the microstructural observation was carried out to investigate the joint deformation behavior in the dynamic load. It was obvious that the plastic deformation capacity of the Sn37Pb joints was remarkably higher than the one of the Sn3.8Ag0.7Cu joints, proving that most of SnAgCu-based solders presented low deformation compatibility and low energy absorption.

Using Carrier Fringes to Study the High Temperature Deformation Behavior of a BGA Package Under Extended Dwell Times

There is a compelling need to experimentally understand solder joint deformation behavior at high temperatures over an extended period of time. Accordingly, the deformation behavior of solder joints in a Ceramic Ball Grid Array (CBGA) package mounted on an organic FR4 board under extended dwell time at a high temperature has been studied using laser moire interferometry. The warpage and the in-plane horizontal deformation of the ceramic substrate and the organic board as a function of time were determined. The variation of the normal strains and shear strains in the solder joints with time were also investigated. It was found that increased sensitivity was necessary to accurately determine the strains in the small sized solder joints. A new method utilizing carrier fringes to increase the sensitivity of the moire interferometry system is proposed and has been used to determine the strains in the small sized solder joints. Increased sensitivity can be obtained merely by changing the incident angle of the laser light on the surface of the specimen, thereby making it unnecessary to use expensive phase shifting apparatus with the traditional laser moire system.

Increasing strength of single lap joints of metal adherends by taper minimization

The effect of tapering the ends of the adherend on the joint strength and joint deformation behavior of a single lap joint geometry was studied. The joints were geometrically modeled using finite element (FE) techniques involving linear, as well as nonlinear (bilinear) material behavior. The FEA results were then compared with the experimental results for different single lap configurations, which had aluminum and steel adherends with different surface etch conditions, bonded using two different adhesives. The FEA results were found to be consistent with the experimental results with the normal and shear stresses significantly decreasing in the modified (tapered) geometries over those in unmodified geometries. The joint strength increased with decreasing taper angle, reaching a maximum at the smallest value considered (~10°).