Friction drilling is a green hole-making process that zealously utilizes the heat generated from the friction between the rotating conical tool and workpiece to create a bushing without generating chip. The difficult-to-machine materials with unique metallurgical properties have been developed to meet the demands of extreme applications. However, the major challenges of friction drilling on difficult-to-machine materials are the hole diameter accuracy, petal formation and tool wear. In this study, the effects of process parameters such as spindle speed and feed rate on bushing height and shape, hardness and tool wear in friction drilling of titanium alloy Ti-6Al-4V were experimentally investigated using tungsten carbide tool. Optical photographs have also been analyzed for better understanding of the chipless friction drilling process for different parametric settings. Experimental results indicated that the spindle speed has great influences for achieving better bushing formation and prolong the tool life. It was confirmed that the low spindle speed and low feed rate have great influences for achieving better bushing shape and height, prolong tool life and lower hardness that located adjacent to the hole wall. It also was discovered that the low thermal conductivity of Ti-6Al-4V caused to improper increment of frictional heat and surface temperature. This disadvantage leads to unsatisfactory bushing formation. This work demonstrated the performances of chipless friction drilling used on difficult-to-machine material that can offer a great prospective for a new product design and manufacturing.

This paper describes laboratory tests on twelve simply-supported one-way slabs including four lightweight concrete slabs in this study and previously conducted experiments on eight self-compacting reinforced concrete slabs subjected to loading at the age of 14 days. All slab were identical by dimensions of 3.8 m long supported on 3.5 m span, 400 mm wide, and 161 mm deep with 4N12 bars at an effective depth of 136 mm providing a reinforcement ratio of 0.008. After seven days moist-curing, the specimens were removed from the formworks and subjected to different values of the uniformly distributed loading including the self-weight of slabs. The mid-span deflection of slabs was recorded immediately after putting the loading blocks on the slabs. Despite close values of the compressive strength of the mixtures, the obtained results validate the effect of the concrete type on the instantaneous deflection of slabs. A wide range of existing models of the effective stiffness of reinforced concrete section were investigated to predict the instantaneous deflection of slabs. Majority of the models are developed for conventional concrete. Comparing the predicted and experimental results of mid-span deflection confirmed that the existing models are inadequate for lightly reinforced specimens such as slabs. New models are proposed and verified to predict the effective moment of inertia in the slabs with and without fiber reinforcing concretes.

An in-house finite element code was utilized to evaluate mode I/II stress intensity factor (SIF) of an edge cracked semi-circular disc subjected to three-point bending. The specimen was considered as an isotropic and homogeneous material. Relative span length ratios of 0.3 to 0.8 in steps of 0.1 were invoked. Relative crack length ratios of 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were analyzed with crack angles up to 60° in steps of 5°. At the same crack length, mode I SIF decreases with increasing crack angle or decreasing the span length. The range of pure mode II decreases with increasing the span length. For the same crack length, the crack angle corresponding to the transition from a mixed mode I/II to a pure mode II increases with increasing the relative span length ratio. On the contrary, that angle decreases with increasing the crack length for the same span length. Good agreement has been generally obtained with relevant results found in the literature.

Linear matching method (LMM) is one of the effective numerical methods for the limit and shakedown analysis, which computes the converging upper series by solving iteratively linear elastic analysis with Young’s modulus varying in space. LMM, which is capable of implementing by using the commercial finite element packages such as ABAQUS and ANSYS has been widely used in the practical applications including fatigue, creep and composite analysis. Nevertheless, LMM could not ensure numerical accuracy for discontinuous problems such as crack analysis since it computes the mechanical quantities including stress, strain and displacement on the base of conventional finite element method, likewise other numerical methods for the limit and shakedown analysis. Meanwhile, extended finite element method (XFEM), recently proposed, is an attractive numerical method for the analysis of discontinuous problems which enriches finite element approximate space by some special functions. In this paper, authors proposed a very straightforward method for the limit analysis by the combination of XFEM with LMM. Numerical validation is done for two types of typical fracture specimens. Numerical examples show that the limit analysis by combining XFEM with LMM gives more accurate result compared with the one by combining of conventional finite element method with LMM. Furthermore, we demonstrated that the choice of enrichment region plays an important role in the improvement of numerical accuracy of our proposed method.

Friction Stir Welding (FSW) is a relatively new solid state joining technique which is used not only for joining the aluminum and its alloys but also has potential for joining dissimilar materials with very different physical and mechanical properties which are hard to weld using conventional fusion welding processes. Tensile shear testing is used to determine the Mechanical strength of friction stir lap (FSL) welds under static loading, fracture strength (σLap) corresponding to the maximum load in a test over the sample width is widely used as the strength value. During friction stir lap welding (FSLW) of dissimilar metals with large differences in melting temperatures, a metallurgical bond is established through the formation of interfacial intermetallic compounds. However, as these intermetallic compounds are generally believed to be brittle with little ductility, they are generally considered to have detrimental effect on fracture strength. The aim of the present research is to study how the interface structure is affected by FSW parameters and how the formation of interface structure affects fracture of Al-Steel and Al-Ti FSL welds.

The interphase is a region between fibers and a matrix, which has different properties from the matrix and the fibers, but is dependent on them. Considering the interphase region has a significant effect on the accuracy of obtained residual stresses. So far, in order to obtain the micromechanical residual stresses, the interphase properties are considered as an average. In this paper, the properties of the interphase are assumed variable by using a suitable UMAT code in the ABAQUS software. The equations of previous studies that have acquired interphase properties to be variable are used to write the UMAT code. A representative volume element (RVE) in polymer composites is modeled in three phases in the ABAQUS software and the interphase properties are considered as FGM by using the UMAT code. Temperature variation during curing to environment temperature is the only loading factor in the RVE. The matrix, fiber and interphase stresses are obtained in the ABAQUS software. The achieved stresses were compared with the results of previous studies that considered interphase properties as average. Finite element and energy methods were used in previous papers but in the present study just the finite element method with variable interphase properties was use. In addition, residual stress diagrams with the variable interphase properties are plotted to study the effect of the thermal expansion coefficient. The results of this study are similar to those in previous ones, and the curves are improved.

Thermal deformations can reduce the product quality that causes loss of dimensional control and structural integrity. It may increase the manufacturing cost due to unfitted component. This paper deals with the thermal deformation on AA6061 aluminum alloy T-joint after exposed to heat by gas metal arc welding (GMAW) process. In this study, two main parameters; welding speed and welding voltage were used to evaluate the angular distortion, transverse shrinkage and longitudinal shrinkage occurred in GMAW process. The results show that the angular distortion is larger with lowest welding speed. The transverse shrinkage is reduced gradually with increasing of welding speed and transverse shrinkage also linearly increasing with increasing of welding voltage. The magnitude of longitudinal shrinkage is much smaller than angular distortion and transverse shrinkage. Longitudinal shrinkage is insignificantly affected by changing the welding heat input. These findings are important to identify and minimize the unacceptable welding distortion in product manufacturing.

In this article, waste plastics (low-density polyethylene, LDPE) and crumb rubber have been utilized to solve one of the most important environmental issues and to improve bitumen performance properties by these low cost materials. At first, modified bitumen samples were made using high shear mixer, then classic and performance tests were performed on them. It has been observed that adding low-density polyethylene and crumb rubber to the bitumen leads to improvement of classical characteristics. Then, after conducting dynamic shear rheometer test on modified bitumen samples, it was found that the sample containing 3% LDPE and 3% crumb rubber has the best performance. Conducting short-term and long-term aging experiments on samples containing 3% LDPE showed improved performance at high temperature services. After BBR test, more appropriate performance grade is observed for the sample containing 3% LDPE 3% crumb rubber.

This paper deals with the elastica and buckling loads of the nonlinear elastic tapered cantilever columns subjected to an axial load at the free end. The column cross section is rectangular, where the width and depth vary linearly with the column axis. The column material is nonlinear elastic, which obeys the Ludwick’s constitutive law. The ordinary differential equations governing the elastica of buckled column are derived and solved numerically for computing the elastica and buckling loads. Parametric studies for the annealed copper, N.P. 8 aluminum alloy and steel columns are conducted

This work is focused on the influence of different friction stir welding (FSW) parameters on AA6082 T-6 and AA5083-O alloys welding quality, by using Taguchi, Grey Relational and Weight Method. Four welding parameters were investigated, namely tool rotation speed (TRS), welding speed (WS), tool pin profile (TPP) and shoulder diameter (SD). The optimized setting of these input parameters was investigated so that weld parts quality could be optimized. Analysis of variance (ANOVA) was used to investigate the effects of these welding process parameters on response variables, viz. elongation (EL) and ultimate tensile strength (UTS). Single response optimization was carried using Taguchi Technique while grey relational analysis (GRA) was used for simultaneous optimization of two responses. Once the optimal settings of control factors were identified, confirmation experiments were performed for the validation of results. In the multi-response optimization, TRS was found to have the maximum effect (57.9%), followed by WS, SD and TPP. Weight method was applied for providing the priority to the response (i.e. EL and UTS). The response with higher priority presented a weight equal to 0.7, while the lower priority given corresponds to a weight of 0.3.