Material Testing under Tension

Types of Testing There are two types of testing Destructive testing Non-Destructive testing Destructive testing is changes the dimensions or physical and structural integrity of the specimen. (It is essentially destroyed during the test) e.g., Tensile, Compression, Shear and Rockwell Hardness Non-Destructive testing does not affect the structural integrity of the sample. ( A measurement that does not effect the specimen in any way) e.g., weighing, measurements etc.

Mechanical Testing Ultimate Tensile Strength - The maximum tensile stress that a material is capable of developing during a test. Load- Applied force either pounds or Newton's Stress - The intensity of the internally-distributed forces or components of forces that resist a change in the form of a body. Commonly measured in units dealing with force per unit area, such as pounds per square inch (PSI or lb/in2) or Mega pascals (Mpa). The three basic types of stress are tension, compression, and shear. The first two, tension and compression, are called direct stresses. Elastic Limit - The greatest amount of stress a material can develop without taking a permanent set. Percent Elongation - The total percent strain that a specimen develops during testing.

Mechanical Testing Modulus of Elasticity - Also known as Young’s modulus; calculated by finding the slope of the stress-strain curve for a given material within the range of its linear proportionality between stress and strain. Proportional Limit - The greatest stress a material can develop without deviating from linearity between stress and strain. Otherwise stated, the greatest stress developed in a material within its elastic range. Percent Reduction in Area - The difference between the original and final cross-sectional areas of a test piece, expressed as a percentage. Yield Point – Also referred to as Elastic Limit, is the point at which any additional stress will result in permanent deformation. Yield Strength - The stress at which a material exhibits a specified limiting permanent set.

Tensile Test - Introduction The tensile test is a common test performed on metals, wood, plastics, and most other materials. Tensile loads are those that tend to pull the specimen apart, putting the specimen in tension. They can be performed on any specimen of known cross-sectional area and gage length to which a uniform tensile load can be applied. Tensile tests are used to determine the mechanical behavior of materials under static, axial tensile, or stretch loading. stress strain P is the load in lbs A0 is the original cross-sectional area near the center of the specimen. l is the gage length at a given load l0 is the original gage length with zero load

Material Fracture: Background This stress-strain curve is produced from the tensile test. Stress-Strain Curve

Tensile Testing - Procedure Tensile tests are used to determine the tensile properties of a material, including the tensile strength. The tensile strength of a material is the maximum tensile stress that can be developed in the material. In order to conduct a tensile test, the proper specimen must be obtained. This specimen should conform to ASTM standards for size and features. Prior to the test, the cross-sectional area may be calculated and a pre-determined gage length marked. The specimen is then loaded into a machine set up for tensile loads and placed in the proper grippers. Depending on the material and specimen being tested, data points may be more or less frequent. Data include the applied load and change in gage length. The load is generally read from the machine panel in pounds or kilograms. The change in gage length is determined using an extensometer. An extensometer is firmly fixed to the machine or specimen and relates the amount of deformation or deflection over the gage length during a test. While paying close attention to the readings, data points are collected until the material starts to yield significantly. This can be seen when deformation continues without having to increase the applied load. Once this begins, the extensometer is removed and loading continued until failure. Ultimate tensile strength and rupture strength can be calculated from this latter loading. Once data have been collected, the tensile stress developed and the resultant strain can be calculated. Stress is calculated based on the applied load and cross-sectional area. Strain is the change in length divided by the original length.

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