Page 255 - CITS - Welder - Trade Theory

WELDER - CITS

Mechanical Testing of Metals. Principles, Applications of

- Hardness testing (Rockwell and Brinell) - Impact testing

(Izod and Charpy) - Tensile testing and Bend Test

Objectives : At the end of this lesson you shall be able to
• describe the mechanical testing of metal
• explain the hardness testing
• explain the impact testing.

1 Introduction: The mechanical properties are those which affect the mechanical strength and ability of a
material to be molded in suitable shape. Some of the typical mechanical properties show huge applications in
space and automobile industries. These properties are associated with the capability of the materials to resist
mechanical forces and load and they are measured in terms of the behavior of the material when subjected to
a force. Mechanical properties may be determined to provide either design data for the engineer or as a check
on the standard of raw materials
1 Mechanical properties may be changed by heat treatment process and the working temperature. Mostly,
the strength, toughness and hardness of materials are to be measured after the metal forming process

2 The main objective of the paper is to give the overview of the importance of mechanical properties of the
materials, testing. This paper, includes the concepts of strength, plasticity, malleability, stiffness, elasticity,
brittleness, ductility, toughness, resilience, fatigue, creep and shown how improper understanding of
properties can lead to have confusion. The engineering concepts of mechanical. properties dominate the
teaching in the technological universities over natural sciences.
2 Mechanical Properties Definition : Strength and Stress-Strain Curve Strength of the materials refers to the
ability of a material to resist the externally applied forces without breaking or yielding. The maximum stress is
that any material withstands before destructive is called its ultimate strength (D). Fig 1 shows the stress and
strain relationship. Stress and strain curve of the material obtained during tensile test describe its ductility and
yield strength. According to Fig 1, upto the elastic limit, the elasticity of material, that means the material would
return to its original dimension, would be maintained, over it the plasticity would follow. Once the material
exceeds the ultimate stress point (D), necking starts to have on the specimen. The strain hardening is kept
between yield points to ultimate tensile strength. A material obeys hooks law upto proportional limit accurately.
The stress and strain curve is used to obtain Young‘s modulus of materials by comparing stress and strain
value upto elastic limit. In the figure, A-B range is measured as elastic limit. The Ability of materials to sustain
loads without undue failure or distortion is known as strength and it is known that the ability of a material
to provide an equal reaction to an applied force (tensile, compression, shear) without rupture. Simply, the
strength is a maximum resistance by the material to the deformation. Similarly, tenacity is the ability of a
material to resist rupture due to a tensile force.

Fig 1

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CITS : C G & M - Welder - Lesson 83 - 97