Experiment. A wealth of information about a material's mechanical behavior can be determined by conducting a simple tensile test in which a round shaped or a flat specimen of uniform cross-section is pulled until it divides or fractures into separate piec

Authors Avatar

IŞIK ÜNİVERSİTESİ

Department of Mechanical Engineering

ME 301 Measurement and Instrumentation

LAB REPORT 4

19.11.2009

PREPARED BY

ONUR EMRE KÖSE

207ME2051

ABSTRACT

        The mechanical properties of a material are directly related to the response of the material when it's subjected to mechanical stresses. Since characteristic behavior occur at discrete engineering stress and strain levels, the basic mechanical properties of a material are found by determining the stresses and corresponding strains for various critical occurrences. A wealth of information about a material's mechanical behavior can be determined by conducting a simple tensile test in which a round shaped or a flat specimen of uniform cross-section is pulled until it divides or fractures into separate pieces. The original cross sectional area, Ao, and gage length, lo, are measured prior to conducting the test and the applied load and gage displacement are continuously measured throughout the test using computer-based data. Based on the initial geometry of the sample, the engineering stress-strain behavior (stress-strain curve) can be easily generated from which numerous mechanical properties, such as yield strength and elastic modulus, can be determined. Universal testing machines, which can be hydraulic or screw based, are generally utilized to apply the test displacement/load in a continuously increasing manner according to ASTM specifications.

INTRODUCTION

        The tensile test consists on the application of a tensile stress on a chosen specimen

attached to a device that calculates the force applied on it and the elongation. The

graph of the stress against the elongation allows the engineers to determine the elastic

and plastic region of a metal which are respectively located on the left and right sides

of the yield point. The metal has a plastic behaviour in the elastic region which means

that it will retake its original form after deformation. However once the yield point is

reached, the deformation applied to metal will be definitive as it is now located in the

plastic region.

          The metal will sustain the load until it reaches the fracture point preceded by the ultimate tensile strength which is the maximum load that a metal can sustain during a tensile test.

The data collected from the tensile test can be analysed using the following formula to

determine the Stress, Strain and Tensile modulus.

Stress = Area / Force

Strain = Extension / Original Length

Tensile modulus = Stress / Strain (in the elastic region)

The Yield Stress, Proof stress, Tensile Strength and Elongation can also be calculated

using the following relations:

 Yield Stres Re = Tensile force at yield point / Original cross sectional area of specimen

Proof Stress = Stress occuring at a strain of 0.002 or %0.2

Tensile Strength = Maximum tensile force in test / Original cross sectional area

Elongation = ( lf-lo) / lo    where  lo=original gauge length

                                                    Lf=gauge length at fracture

INSTRUMENTATION and PROCEDURE 

        A Universal Testing Machine otherwise known as a materials testing machine/ test frame is used to test the  and  properties of materials. The Universal Testing machine is named so because it can perform all the tests like compression, bending, tension, etc. to examine the material in all mechanical properties Such machines generally have two columns but single column types are also available.  and  measure the key parameters of  and  as the sample is tested. These machines are widely used and would be found in any materials testing laboratory.

A typical testing system consists of a materials testing machine/test frame, control and analysis software, and critically, the test fixtures, accessories, parts and devices used to hold and support the test specimen.

Join now!

A tension test is a destructive test in the sense that the specimen is finally broken or fractured into two pieces. To perform the tensile test, the universal testing machine should be capable of applying that load which is required to break or fracture the material.

The test piece or specimen of the material is generally a straight piece, uniform in the cross-section over the test length and often with enlarged ends which can be held in the machine grips. However, the machine can hold the specimen without enlarged ends also.

Many decades ago before the birth of digital sensor ...

This is a preview of the whole essay