Fabrication and testing of Al–SiCp composite poppet valve guides

Composite materials are replacing the materials used in various fields and are the candidate materials for future growth. Metal matrix composites are the class of composite materials finding vast applications in automotive, aircraft, defense, sports, and appliance industries. In the present work, Al–SiC_p composites with 5–30 wt.% of SiC particulates were fabricated using powder metallurgy as well as casting processes. Mechanical alloying of aluminum and SiC particles was done prior to compaction so as to enhance the properties of the fabricated powder metal components. A custom built sliding valve guide wear test rig was fabricated to simulate the valve stem/guide wear under cold start condition of an engine by reciprocation of a valve stem under different imposed loads, against a stationary poppet valve guide. The hardness and radial crushing load was measured for the Al–SiC_p composite poppet valve guides and were found better than the cast iron poppet valve guides presently used in engines. The wear test of the poppet valve guides was done using valve guide wear test rig, which revealed that the Al-20 wt.% SiC_p and Al-30 wt.% SiC_p composite poppet valve guides have higher wear resistance than the cast iron poppet valve guides. The hardness, radial crushing load, and wear resistance of Al–SiC_p composite poppet valve guides were found to increase with increase in weight percent of SiC_p. The microstructural analysis of the cast and PM Al–SiC_p composites was also done using scanning electron microscope. Finite element analysis of the Al–SiC_p composite poppet valve guide was also done using Ansys software, which supports the successful implementation of the Al–SiC_p composite poppet valve guides for automobiles.     

Ultrastructural analysis of cell wall of drug resistant and sensitive Mycobacterium tuberculosis isolated from cerebrospinal fluid by transmission electron microscope

Drug‐resistant tuberculosis is being increasingly recognized and is one among the leading cause of death worldwide. Remarkable impermeability of cell wall to antituberculous drugs protects the mycobacteria from drug action. The present study analyzed the cell wall thickness among first‐line drug resistant and sensitive Mycobacterium tuberculosis (Mtb) isolated from cerebrospinal fluid by transmission electron microscopy (TEM). The average thickness of the cell wall of sensitive isolates was 13.60 ± 0.98 nm. The maximum difference (26.48%) in the cell wall thickness was seen among multi‐drug resistant (18.50 ± 1.71 nm) isolates and the least difference (4.14%) was shown by streptomycin‐resistant (14.18 ± 1.38 nm) isolates. The ultrastructural study showed evident differences in the cell wall thickness among sensitive and resistant isolates. Preliminary TEM examination of cells indicates that morphological changes occur in the cell wall which might be attributed to the drug resistance. The thickened wall of Mtb appears to help the bacilli to overcome the action of antituberculous drugs.     

A PC-based system integrating CMM and CAD for automated inspection and reverse engineering

A personal computer (PC)-based system integrating a manual CMM and a CAD system has been developed for on-line capture of 3D point data, resulting in the automation of the inspection process. The sequence of steps taken to measure a master component using the CMM is stored in a measurement program in teach mode and replayed for repetitive measurement of a batch of identical components in the replay mode. The measurement program guides the CMM operator regarding the geometric entity to be measured, the number of points to be input and the direction to be followed for taking the points on the CMM. The operator has simply to follow the sequence displayed on the computer screen. The program automatically computes the dimensions and the deviations from the corresponding dimensions of the master component. The 3D measurement data from the CMM are transferred to a CAD system in real time. Programs have been developed to create 3D cubic splines and surfaces from the 3D point data taken on the CMM. The full features of the CAD software can be used to manipulate the 3D point data for CAD applications.     

Fabrication and testing of Al-SiCp composite valve seat inserts

In the present work Al-SiC_p composite valve seat inserts with 10, 15, 20, and 25 wt?% of SiC_p were fabricated through die compaction of powders and subsequent sintering at 580 °C. Valve seat inserts were also fabricated through the gravity die casting process. The Rockwell hardness, density, radial crushing load and surface roughness of the Al-SiC_p composites (with different wt % of SiC_p) and steel valve seat inserts presently used in engines were measured and compared. The Rockwell hardness and radial crushing load for Al-15, 20, and 25wt% of SiC_p composite valve seat inserts were higher than that of the steel valve seat inserts presently used in engines. The microstructure of the cast and powder metal Al-SiC_p composites was also studied.     

Development of abrasive cut-off wheel having side grooves

The abrasive cut-off wheel fails prematurely during the routine sectioning of workpiece, which may cause injury to the operator. One of the major reasons of premature failure is the improper mixing of the abrasive mixture. In order to provide strength to the wheel, it was reinforced by woven roving type glass fiber and the abrasive mixture was ball milled. Cutting zone temperature becomes high during the cutting operation, which may cause thermal damage to the workpiece and debonding of abrasive from the wheel. It is very difficult to supply the cutting fluid to the cutting zone in order to reduce the temperature. New types of abrasive cut-off wheels were developed, which have radial passages on their surfaces to supply the cutting fluid to the cutting zone. Performance of the wheels was compared and the mechanical strength of the wheel material was tested.     

High Performance Lithium‐Ion Batteries Using Layered 2H‐MoTe2 as Anode

The major challenges faced by candidate electrode materials in lithium‐ion batteries (LIBs) include their low electronic and ionic conductivities. 2D van der Waals materials with good electronic conductivity and weak interlayer interaction have been intensively studied in the electrochemical processes involving ion migrations. In particular, molybdenum ditelluride (MoTe₂) has emerged as a new material for energy storage applications. Though 2H‐MoTe₂ with hexagonal semiconducting phase is expected to facilitate more efficient ion insertion/deinsertion than the monoclinic semi‐metallic phase, its application as an anode in LIB has been elusive. Here, 2H‐MoTe₂, prepared by a solid‐state synthesis route, has been employed as an efficient anode with remarkable Li⁺ storage capacity. The as‐prepared 2H‐MoTe₂ electrodes exhibit an initial specific capacity of 432 mAh g^?1 and retain a high reversible specific capacity of 291 mAh g^?1 after 260 cycles at 1.0 A g^?1. Further, a full‐cell prototype is demonstrated by using 2H‐MoTe₂ anode with lithium cobalt oxide cathode, showing a high energy density of 454 Wh kg^?1 (based on the MoTe₂ mass) and capacity retention of 80% over 100 cycles. Synchrotron‐based in situ X‐ray absorption near‐edge structures have revealed the unique lithium reaction pathway and storage mechanism, which is supported by density functional theory based calculations.