Sohail M.A. Khan

Effect of temperature on the mechanical properties of polypropylene–talc composites:

In this study, the effect of the temperature and talc concentration on the mechanical properties of the polypropylene (PP) + talc composite is analysed. Tensile, impact, bending and dynamic mechanical tests were carried out to evaluate the mechanical properties of PP + talc composite and to analyse the effect of temperature variation on these properties. The obtained results show that the temperature increase has a very negative effect on the mechanical strength of the PP–talc composite but it can be significantly reduced by the augmentation of the talc content.

Fatigue crack propagation in aluminum plates with composite patch including plasticity effect

In this paper, we analyzed experimentally and numerically the behavior of fatigue crack in aluminum plates repaired with bonded composite patch. We studied the behavior of repaired crack in AA 2024 T3 and AA 7075 T6 under two levels of applied fatigue stresses: maximal stresses of 70 and 120 MPa at a load ratio of 0.1. In the experimental part, the fatigue life of unrepaired and repaired notched specimens were determined. In the numerical part, the J integral around repaired and unrepaired crack tips was calculated. The numerical and the experimental results were used to plot the crack velocity (da/dN) as a function of the J integral. The analysis was completed with scanning electron microscopic observations on fracture surfaces of repaired and unrepaired specimens. It was found that patch improves the fatigue life but this improvement is considerably reduced with the increase in the applied fatigue load. The Al 2024 T3 presents better resistance to fatigue crack propagation in both repaired and unrepaired cases.

Specific crack enthalpy as material characterization parameter

Abstract In this study, the specific crack enthalpy (damage), considered a material characterization parameter according to crack layer theory, is discussed. The crack region and its accompanying damage become a crack layer. Fatigue crack propagation experiments were conducted on HT60 and HT80 steel. The specific enthalpy γ* of fracture due to ductile crack propagation in steel HT60 and HT80 has been calculated. The energy release rate and damage coefficients were determined at different stress ratios varying from R = 0.04 to 0.8. The crack layer translational resistance moment R1 has been determined. Because interpreting the data of crack propagation on two types of steel in the light of this theory reveals reasonable similarity, the need to set up experiments specifying the limitations and applicability of the theory is essential.

Evaluation of residual stresses present in spirally welded API grade pipeline steel using the hole drilling method

Abstract The mechanical and microstructural characterization of a material prior to its installation for the desired service is imperative to avoid material or structural failures. Of the several mechanical properties affecting the performance of a material, the residual stresses (RS) constitute an integral part of the material property and arise mostly during the manufacturing processes. They can be either beneficial or detrimental to material performance depending on their nature and magnitude. In this study, the microhardness, the tensile and the nature and magnitude of RS present in the weldment zones, base material (BM), heat affected zone (HAZ) and weld nugget (WN) of spiral welded (SWP) API grade line pipe steel, were determined. The microhardness and tensile responses were observed to have significant demarcation depending on the location where examined. The RS were measured using a nondestructive X-ray diffraction (XRD) and a semidestructive hole drilling (HD) technique. The results from both measurement techniques are found to be in good agreement. The BM microstructure consisted of ferrite and pearlite phases with ferrite constituting the dominant phase. The WN comprised of multi-passes, which consisted of root (hot) and the reinforcing (filling) pass. The microstructure of the reinforcing passes can be described as columnar grains/structure.