Introduction to Basic Manufacturing Processes and ... - always yours

126 Introduction to Basic Manufacturing Processes and Workshop Technology
Poisson’s Ratio
The ratio of lateral strain to linear strain in metal is called poisson’s ratio. Its value is
constant for a particular material but varies for different materials.
Proof Resilience
The maximum amount of energy which can be stored in an elastic limit is known as
proof resilience.
Modulus of Resilience
The proof resilience per unit volume of a material is modulus of resilience or elastic toughness.
7.3.3 Testing of Hardness
It is a very important property of the metals and has a wide variety of meanings. It embraces
many different properties such as resistance to wear, scratching, deformation and machinability
etc. It also means the ability of a metal to cut another metal. The hardness of a metal may
be determined by the following tests.
(a) Brinell hardness test
(b) Rockwell hardness test
(c) Vickers hardness (also called Diamond Pyramid) test
(d) Shore scleroscope
Fig. 7.9 shows Rockwell hardness testing machine.
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1. Indicator.
2. Indentor holder.
3. Indentor.
4. Screw.
5. Screw wheel.
6. Weight.
7. Load.
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Fig. 7.9 Rockwell hardness testing machine
7.3.4 Testing of Impact Strength
When metal is subjected to suddenly applied load or stress, it may fail. In order to assess the
capacity of metal to stand sudden impacts, the impact test is employed. The impact test
measures the energy necessary to fracture a standard notched bar by an impulse load and
as such is an indication of the notch toughness of the material under shock loading. Izod test
and the Charpy test are commonly performed for determining impact strength of materials.
These methods employ same machine and yield a quantitative value of the energy required
to fracture a special V notch shape metal. The most common kinds of impact test use notched
specimens loaded as beams. V notch is generally used and it is get machined to standard
specifications with a special milling cutter on milling machine in machine shop. The beams
may be simply loaded (Charpy test) or loaded as cantilevers (Izod test). The function of the