Çınar Yeni

Effect of Pin Penetration Depth on the Mechanical Properties of Friction Stir Spot Welded Aluminum and Copper

Abstract The effect of pin penetration depth on the mechanical properties of friction stir spot welded (FSSW) aluminum alloy 1050 and pure copper has been investigated. For a certian tool geometry, constant tool rotation speed and penetration time, the materials have been friction stir spot welded in three different penetration depths, namely 2.8 mm, 4 mm and 5 mm. Tensile shear tests, microhardness measurements and micostructural investigation have been carried out on the welded specimens in order to investigate the effect of penetration depth. 2.8 mm plunge depth has resulted in a weak joint, whereas 4 mm and 5 mm plunge depths offer acceptable tensile shear results. Presence of intermetallic phases had an influence on the tensile shear and hardness values.

Application of the Taguchi method for the optimization of the strength of polyamide 6 composite hot plate welds

Abstract The purpose of this study is to investigate the influence of the welding parameters in the hot plate welding process of polymer composites, polyamide 6 glass fiber reinforcement 15 wt.-%, by using the Taguchi method. Four welding parameters, namely the plate temperature, heating time, welding displacement and welding time, were optimized under the consideration of the joint strength. The Taguchi approach of the parameter design was used as a statistical procedure to set the optimal welding parameters. For hot plate welding of the specimens, the combination of process parameters based on three levels of the L9 orthogonal array was utilized. The signal to noise and the analysis of variance were employed to find the optimum levels and to indicate the impact of the welding parameters on joint strength by tensile tests of welded joints. It was shown that choosing 270 °C as plate temperature, 1.0 mm of weld displacement and 25 s of heating time, reveals an improved joint strength. For the optimized parameters it was verified that the welding time does not have a significant influence and the most effective factor on joint strength is the plate temperature. The weld displacement and heating time only slightly influenced the joint strength. A confirmation run was also performed to prove the effectiveness of the Taguchi method after determination of the optimum levels of the process parameters. The results showed that the joint strength was improved by about 27 % as compared to the initial welding parameters and the joint efficiency increased from 56 % to 71 %.

Effects of post-weld heat treatment on the microstructural evolution and mechanical properties of dissimilar friction stir welded AA6061+SiCp/AA6061-O joint

A research on the microstructure and mechanical properties of the dissimilar joint was carried out so as to understand the effects of post-weld heat treatment (PWHT) on microstructural evolution, microhardness, tensile and flexural properties of the dissimilar friction stir welded (FSWed) joint. The results showed that there is a sufficient and rather complicated material mixing in the nugget zone (NZ). After PWHT, the grains in the joint area except for the NZ demonstrated a grain refinement with more homogeneous and equiaxed grains. Fine and clustered SiC particles in the NZ are confirmed by scanning electron microscope (SEM). In addition, the microhardness values of nugget zones both in as-welded and PWHT condition exhibited a higher Vickers compared to that of AA6061-O. Furthermore, a mean tensile strength of 183.30 MPa that demonstrates a 52.22% increase in tensile strength is also observed in the transverse tensile tests subsequent to PWHT. Considering the three-point bending test results, it is explicit that an increase of 121.96% in the bending extension is obtained as there is no significant increase in maximum bending force after the PWHT.

Optimization of welding parameters of hot plate welded PC/ABS blends by using the Taguchi experimental design method

This study aims to investigate the influence of welding parameters in hot plate welding (HPW) process of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blends using Taguchi method. Three welding parameters, namely the plate temperature, heating time, and welding displacement, were optimized in terms of joint strength using the results of tensile tests. Taguchi experimental design method is implemented as a statistical design of experiment technique so as to set the optimum welding parameters and determine the optimal levels. For HPW of the specimens, the combination of process parameters based on three levels of L9 orthogonal array was utilized. The signal to noise ratio and the analysis of variance were employed to find the optimum levels and to indicate the impact of the welding parameters on joint strength after tensile tests of the welded joints were carried out. It was shown that it might achieve the improved joint strength using 290 °C of plate temperature, 1.25 mm of welding displacement, and 25 s of heating time. For the optimized parameters, it was verified that the most effective factor on joint strength is plate temperature and second effective factor is welding displacement and heating time only slightly influenced on joint strength. After the optimum levels of process parameters are set, in order to demonstrate the effectiveness of Taguchi method, a confirmation run is also performed. An improvement by about 70% from initial welding parameters was observed, and joint efficiency has increased from 22.5% to 38.2% regarding base material properties.

Mathematical Modelling of Vibration Response Characteristics for Dissimilar Hot Plate Welded Polyamide 6 Composite Beams

Abstract This study is concerned with the mathematical modelling of the vibration response characteristic of a special dissimilar composite beam based on experimental modal analysis. Here, experimental modal analyses of three different dissimilar polyamide 6 composite beams, which are connected to each other by hot plate welding are performed. The measured natural frequencies are compared with finite element predictions for verification purposes. Modal information obtained by experiments is used to construct a mathematical model representing vibration response characteristic of beams by applying multi degree of freedom curve fitting method. The model showing modal characteristics of dissimilar beams is now ready to be used in different kinds of excitations to predict the frequency response of vibration.

Investigation of strength mis-match effect on elastic plastic fracture parameters in laser beam welded aluminium alloy joints using the finite element method:

In this study, elastic plastic fracture toughness parameters of laser-welded 6013 aluminium alloy are investigated. For this purpose, compact tension specimens used in the experimental study are modelled using the finite element software. In the analyses, crack tip opening displacement (δ5) and J-integral values are determined and crack tip opening displacement, δ5 and J-integral resistance curves (R-curves) are generated. Crack tip opening displacement, δ5 resistance curves are compared with those obtained from the experimental work, and J-resistance curves are compared with those obtained from formulation. Effect of weld strength undermatching on crack tip opening displacement, δ5 and J-resistance curves is discussed. δph values obtained by the plastic hinge method are compared with the crack tip opening displacement, δ5 values. Fracture toughness parameters obtained from the finite element analysis showed a good agreement with those obtained from the experimental work and formulation. It is observed that the resistance curves obtained using the crack tip opening displacement, δ5 and J-integral characterize the resistance of the material against crack growth in a similar manner, and strength undermatching decreases the fracture resistance. The relationship between δph and crack tip opening displacement, δ5 is nonlinear, and as crack tip opening displacement increases, crack tip opening displacement, δ5 becomes larger than δph.

Determination of Elastic Plastic Fracture Toughness Parameters for a Compact Tension Specimen Using the Finite Element Method

Abstract In this study, elastic-plastic fracture toughness of an aluminum alloy is investigated. J-integral was calculated using the finite element software and formulation. Crack tip opening displacement (CTOD) is determined by using the plastic hinge model (δph) and direct measurement (δ5). J-Δ a and CTOD-Δ a resistance curves are constructed and compared with those obtained from formulation and those generated from test data, respectively. Good agreement has been obtained between the test results, the formulation and the results of the finite element analysis. The relationship between δph and δ5 is nonlinear and as CTOD increases δ5 becomes larger than δph. The relationship between J-integral and CTOD is found to be linear for both δph and δ5. It has been seen that the proportionality constant dn considerably depends on the method of calculation of CTOD.

Mechanical and Microstructural Behaviour of Dissimilar Aluminum Alloys Joined by Friction Stir Welding

Abstract In this study, joining of dissimilar aluminum alloys 5059-H111 and 7075-T651 was carried out using friction stir welding. The joint has been investigated in terms of microstructure, hardness and mechanical properties. Optical microscopy was used to characterize the microstructure of the weld area. Seven different zones of the microstructure in the joint can be distinguished. It has been observed that a fine grain structure is formed in the nugget zone as a result of recrystallization. Although there is a general hardness decrease throughout the weld region compared to both base metals, the lowest hardness values are seen at the heat affected and thermo mechanically affected zones of aluminum alloy 5059. The mechanical strength of the dissimilar joint was found to be varying between 56 % to 68 % those of the base metal ultimate tensile strength values. The results show that friction stir welding can be successfully applied for the joining of dissimilar aluminums alloys.