EFFECT OF STRAIN RATE ON THE DEFORMATION BEHAVIOUR OF SHEET STEEL

Abstract

The rate at which a specimen is deformed is an important consideration in the production, fabrication, and testing of materials. This rate can have an important influence on the mechanical properties, particularly the flow stress of material. The aim of the present investigation is to analyze the effect of strain rate on the mechanical behaviour of plain low carbon sheet steel (0.8mm. thick), which contains 0.08 percent carbon. The effect of strain rate has been found out on the as-received, normalized, and annealed conditions. The tensile samples have been cut from the sheet steel along the rolling direction, with the help of a die. The samples were plated with copper by electroless process to prevent decarburisation during heat treatment i.e. annealing and normalizing. The strain rate behaviour of plain low carbon sheet steel has been investigated at the strain rates (speed of loading) of 1,50,100,200,500,750,1000mm/min. TENSOMETER is used in the present investigation for tensile testing. The load versus elongation curves obtained from the test has been replotted into engineering stress-strain curves. Tensile properties i.e. yield stress, ultimate tensile stress, uniform elongation, total elongation, and strain hardening exponent has been reported at above mentioned strain rates. SEM analysis of fractured surfaces has been done to find out the effect of strain rate on the mode of fracture. In general the flow stress (YS, UTS) of as-received, normalized, and annealed steels increases with increase in strain rate. The ultimate tensile stress of as-received steel has been found to increase from 400 MPa to 461 MPa as strain rate increases from lmrn/min. to 1000mm/min. Similarly for normalized steel, ultimate tensile stress increases from 394 MPa to 448 MPa and in case of annealed steel it increases from 294 MPa to 317 MPa as the strain rate increases from Imm/min. to 1000mm/min. The yield M stress of as-received steel has been found to increase from 362 MPa to 415 MPa as strain rate increases from 1mm/min. to 1000 mm/min. Similarly for normalized steel yield stress increases from 309 MPa to 380 MPa and in case of annealed steel it increases from 199 MPa to 257 MPA as the strain rate increases from lmm/min. to 1000mm/min.