The present issue contains five papers. The first paper, “An Experimental and FE Analysis of Helical Gear for Bending Stress at Critical Section”, by Prashant J Patil and M S Patil presents the theoretical as well as experimental results on the effect of pressure angle on bending stress at the critical section of helical gear. With a view to optimizing the process design, the authors evaluated bending stress at critical section of helical pinions of different pressure angles experimentally by 3D photoelastic analysis and strain gauge technique as well as Finite Element Analysis (FEA). In the study, the authors considered different pressure angles and torques for the analysis. The results indicate that the stress values obtained by FEA at 30o pressure angle are in good agreement with those computed theoretically using Lewis equation. At the same angle of 30o, a good agreement is noticed in the bending stress values obtained in both the experimental techniques. Overall, the authors conclude that the bending stress values found in the experimental analysis are less than those evaluated theoretically and by FEA. Their study noted that with the decrease in the pressure angle, the discrepancy in the values increases.

Expansion joints are used in the ducts to absorb dimensional variations caused due to flow of gas at high pressures and temperatures. Occasional failure of the joints is not uncommon. In the paper, “Thermostructural and Dynamic Analysis of Expansion Joint Due to Dynamic Response of Gas Pressure Excitation and Thermal Expansion”, the authors, Chetan Kaduba Mahajan and Ganesh D Korwar, investigated the causes of failure and analyzed the behavior of the 500 mm expansion joint at discharge end of second stage Export Gas Compressor (EGC) for prediction of life using Finite Element and Analytical studies. The analysis, wherein the authors had modeled the shapes similar to the failure of sleeves, yielded results which show that the failure of expansion joints in the EGC piping circuits could be due to cyclic fatigue caused by interaction between the gas flow and the sleeves. Further, the cyclic fatigue is attributed to the variation in pulsating frequency arising due to variation in motor speed. The behavior of expansion joints is found to be dependent upon the relative flexibility versus stiffness of the joint. The authors conclude that attempts to increase or decrease the stiffness and mass combination of the model suitably may yield good results, such that joint is out of resonance zone.

Surface texturing is being widely used for reducing friction in moving parts and improving wear resistance, and to prolong their life with tribological properties of the surface. The micro-dimples reduce friction considerably mainly due to their lubrication retention capability. The properties and geometry of dimples play
an important role in the quantum of reduction of frictional properties of the surface. In the paper, “The Effect of Dimple Density on Tribological Performance of Polyamide (PA66) Composites”, the authors, G S Pendbhaje, V S Aher, A K Mishra and V D Wakchaure, have studied the effect of surface texturing on tribological properties of Polyamide (PA66) composite materials by considering Elliptical texture pattern with varying orientations. The frictional and wear behavior of Polyamide (PA66) composites has been investigated with and without surface texturing on mating surface, at dry and wet lubrication by using a pin-on-disc Tribometer. The coefficient of friction of textured pattern is relatively low when compared with non-textured pattern. Load carrying capacity of textured surface has increased in higher dimple density. The authors conclude that mechanical efficiency and bearing life increase with dimple density in both dry and wet conditions.

The composite materials, composed of two or more distinct phases—matrix phase and reinforcing phase—are used as reinforcements in the form of continuous fibers or discontinuous fibers or particulates or whiskers having bulk properties significantly different from those of any of the ingredients. In recent decades, significant progress has been made in the development of light metal matrix composites for use mostly in the automotive, aerospace and healthcare applications. Hybrid Metal Matrix Composites (HMMCs) are made of two or more number of reinforcements that are integrated into a single matrix material, to get the desirable properties such as equal distribution of reinforcement. Wire Electrical Discharge Machining (WEDM) is extensively used for machining the composite parts with varying hardness or complex shapes with sharp edges that are very difficult to be machined by other machining processes. G Gokulakannan, R V Praveena Gowda and S Ramesh have discussed the problems that are generally encountered in the machining of HMMCs and the future possible research trends in their paper—“Machining of Aluminum Hybrid Metal Matrix Composite by Wire Electrical Discharge Machine: A Review”.

Right selection of ordering policies is one of the important processes for the development of any industry. Numerous selection criteria are related with ordering policies and influenced the ranking of the policies. Based on the available literature, Amit Gupta, in the fifth paper, “Ranking of Ordering Policies by Simple Additive Weighting (Saw) Technique for Indian Automotive Industry”, developed an analytical inventory management model. The author proposed SAW technique to rank the ordering policies against the selection criterion with an objective to reduce the complexity of DBA, and has illustrated it with an example. The proposed model is found to be more helpful and valuable since it offers choices to investigate the final decisions for different set of criterion.

S V Srirama Rao
Consulting Editor