PSI- Issue 9

Tareq Rahman Mahmood et al. / Procedia Structural Integrity 9 (2018) 71–85 Tareq RahmanMahmood, et al. / Structural Integrity Procedia 00 (2018) 000–000

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automation (Pereira et al. 2010)(Hamidinejad, Kolahan, and Kokabi 2012). Due to the large number of spot welds in a particular application such as in one car about 3000–7000, RSW is a critical joining process in vehicle production (Brauser et al. 2010)(Duraffourg et al. 2015). Vehicle crashing and their capability to provide adequate protection to its passengers, depends on the integrity and mechanical performance of the spot welds (Pouranvari 2012b; Pouranvari and Marashi 2010). All welds suffering from cracking either from the weld toe for the traditional weldments, or from HAZ for the spot welded joints (A.M. Al-Mukhtar 2011; A. Al-Mukhtar 2013; Al-Mukhtar 2015, 2009, Al-Mukhtar et al. 2010, 2011; A. Al-Mukhtar et al. 2009; A. M. Al-Mukhtar 2013a, 2013b; A. M. Al-Mukhtar et al. 2009; Al Mukhtar 2002, 2016; A. Al-Mukhtar and Doos 2013; A. M. Al-Mukhtar and Doos 2013; Daws, Al-Douri, and Al Mukhtar 2003). The failure mode of resistance spot welds is a specific measure of mechanical properties (Sadasue et al. 2016). Basically, spot welds can fail in two modes as follows (Pouranvari 2012a)(Al-Mukhtar 2016):  Interfacial failure (IF) mode in which the fracture propagates through the fusion zone (FZ). It is believed that this failure mode has a detrimental effect on the crashworthiness of the vehicles.  Pullout failure (PF) mode in which the failure occurs via withdrawal of the weld nugget from one sheet. In this mode, fracture may initiate in the base metal (BM), heat-affected zone (HAZ), or HAZ-FZ depending on the metallurgical and geometrical characteristics of the weld zone and loading conditions (Al-Mukhtar 2016). The nugget pullout fracture indicates to higher plastic deformation and energy absorption (Al-Mukhtar 2016)(Brauser et al. 2010). The transition from IF to PF mode is generally related to the increase in the size of FZ above a minimum value (Brauser et al. 2010). It has been shown that the minimum fusion zone is a function of sheet thickness, base metals, and HAZ properties as well as the loading conditions (Marashi and Alizadeh-Sh 2015). The goodness of the joint in RSW is directly affected by welding input parameters. The determination of the input parameters is a common problem for manufacturer to get the required strength. Thus, finding the relationships between the strength of spot weld and process parameters have a great interest in related industrial applications. Structures employing RSW joints are usually designed so that these joints are loaded in shear even if the parts are exposed to tension or compression loading, therefore, the tensile–shear strength of spot weld is an important index to welding quality (Marya et al. 2006). Static tensile shear test is the most common laboratory test used to determine weld strength because of its simplicity (Hamidinejad et al. 2012). In recent years, analytical and numerical methods have been employed to model welding processes and to establish the relationships between the weld quality and process parameters. Specifically, several research works are reported on using artificial neural networks (ANNs) to model various welding techniques (Mathew, Kim, and Ryu 2008)(Ates 2007)(Fratini, Buffa, and Palmeri 2009). Optimization of the model was carried out to study other manufacturing processes and applications (Sugandhi and Ravishankar 2012). The process parameters such as composition of zirconia, compaction pressure and sintering temperature were analyzed using Response Surface Method (RSM). The validity of the model was checked and the significant parameters were identified using analysis of variance (ANOVA) (Elsen, Ramesh, and Aravinth 2014). Hence, the strength of the weld was maximized by optimizing the parameters like amplitude, welding pressure and weld time. RSM is a collection of statistical and mathematical methods that are useful for the modeling and analyzing engineering problems. In this technique, the main objective is to optimize the response surface that is influenced by various process parameters.. The using of RSM is developed to predict spot weld quality measure (tensile–shear strength). The present study differ from the existing researches since three different materials; HSLA steel, and low carbon steels in two thicknesses have been considered. The important process parameters considered here include welding current, welding time, electrode force. Next, using design expert program procedure has been employed to determine optimal process parameter values for desired tensile–shear strength. 2. Experimental procedure HSLA Docol 500LA steel, and the low carbon steels have been used. Docol 500LA is widely used in car industry. Low carbon is commercially available. Therefore, it can be used in some parts to be connected with HSLA steel. The chemical composition is shown in table 1. The specimens for tensile test has been prepared according to ASTM E-8