Practice Questions

The Charpy V-notch test involves striking a notched specimen with a pendulum to measure the energy absorbed during fracture. The notch creates a stress concentration and determines the ductile-to-brittle transition temperature

Hardness tests are used to determine the hardness of a material. Rockwell hardness test is a microhardness test that uses a diamond cone or hard steel ball to carry out hardness tests to HRB or HRC scales. Brinell hardness test uses a hard spherical incdenter of 10 mm diameter. Knoop and Vickers hardness tests are micro indentation hardness tests that use a small diamond indenter of pyramidal shape.

Isotropic materials have identical properties in all directions. Metals and glasses are examples. To define the elastic behavior of an isotropic material, only 2 independent elastic constraints are required. Homogeneous materials cannot be separated into different materials and have uniform composition throughout.

The Brinell hardness number for mild steel is 130. The Brinell Hardness Tester consists of a loading system, two ball hard steel indenters, a main screw, and a dial gauge. The indenter tool material is hardened steel and the tool shape is spherical with a diameter of 10 mm.

During a tension test, the fracture occurs on a crystallographic plane known as the cleavage plane, where the normal tensile stress is at its maximum. This test provides information on various mechanical properties of materials such as strength, ductility, and toughness. The results obtained from the test include proportional limit, elastic limit, modulus of elasticity, yield strength, ultimate tension strength, modulus of resilience, modulus of toughness, percentage elongation, and percentage reduction in area.

The Knoop hardness test is a micro indentation hardness test where a small diamond indenter of pyramidal shape is used to force into the specimen. The longer diagonal of the indentation is measured for precise measurement and the Knoop hardness is calculated based on the projected area of the indent. This test is also known as a microhardness test.

The Izod impact test is used to study material behavior under dynamic load conditions. The specimen is positioned like a cantilever beam with a V-notch at the center to initiate a crack. The notch angle in the Izod test specimen is 45°, giving non-uniform stress distribution and less accuracy. The Charpy test uses a simply supported beam with a centrally applied load and a notch to create a stress concentration.

The hardenability of steel is measured by the Jominy end- quench test, which involves quenching a standard cylindrical specimen of austenitized steel with a jet of water at a specific flow rate and temperature. The resulting hardenability curve shows the distance from the quenched end to the location where there is 50% pearlite and 50% martensite, known as the Jominy distance. This test is used to determine the case of martensite formation and is the correct answer for assessing the hardenability of steel.

The toughness test is conducted to study material behavior under dynamic load conditions. Two testis are there- Charpy Impact test and Izod impact test. Charpy impact testing determines temperature-depended ductile-to-brittle transition. A universal testing machine is used to test tensile and compressive strength of materials.

As the mild steel wire is loaded in equal increments till it breaks, the extensions noted with increasing loads will increase uniformly first and then increase rapidly. This is because, after the yield load, further increase in load will cause marked deformation in the whole volume of the metal, leading to a rapid increase in extension. The maximum load which the specimen can withstand without failure is called the load at the ultimate strength.

increase uniformly first and then increase rapidly

When a ductile material is subjected to tensile stress, the maximum shear stress occurs on a plane inclined at 45 degrees to the load. Ductile materials are weak in shear, and failure primarily occurs due to slip in shear along the planes forming approximately 45-degree angles with the axis of the test specimen. This results in a "cup and cone" fracture.

Hardness is the property of a material to resist scratching, abrasion, indentation or wear. There is no absolute scale to measure it.

A Universal Testing Machine (UTM) measures Load and Elongation when performing standard tensile and compressive tests on materials, components, and structures. It is a load-controlled machine that works on the principle of elongation/deformation of material on the application of load.

Engineering Stress and Engineering Strain

Rockwell hardness testing method measures the hardness of a material by the depth of penetration of the indenter. A variety of indenters and loads are used in this method to develop different scales for different materials. Brinell hardness test uses a hard spherical indenter with a diameter of 10 mm and load varying between 500-3000 kg. Hardness is the measure of localized plastic deformation and is related to the size of the resulting indentation.

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