Strength of Materials Lab

1. Torsion testing apparatus.

A torsion testing machine is a device that uses a torsion beam to apply a twist to a specimen and measure the torque necessary to induce failure. Torsion testing machines are helpful in research, development, and production engineering to determine the ultimate tensile strength (UTS) or elastic modulus of materials. A torsion testing machine consists of a lever arm, a torque cell for holding the sample, and a load cell for measuring the torque. Usually, students turn a twist handle to apply force to drive the gears within the machine. It guides a shaft lengthwise from input to output, which allows for any change in length of the specimen during the tests and easy insertion of samples. An encoder measures any tilt or movement relative to continuous rotation. While this does not calculate the rotation angle directly, it displays the angular displacement on an analog display. In addition, another gauge – measuring torsion forces – is built into one or both sides of the drivetrain.

2. Impact testing apparatus.

Impact testing machines evaluate an object's capacity to withstand high-rate loading and it is commonly used to determine the service life of a part or material. Impact resistance can be among the most challenging qualities to measure. There are two standard kinds of impact test, Charpy and IZOD. Charpy tests are commonly performed on metals, but a few plastics and polymers can also be tested. IZOD tests can be performed on either plastic or metal specimens. A Charpy test specimen is usually a 55 x 10 x 10 millimeter bar. An IZOD specimen is typically a 64 x 12.7 x 3.2-millimetre bar.

(a) Charpy impact testing machine.

The tester is equipped with a falling pendulum hammer, able to break, with a single blow, a sample carved in the middle and positioned on two supports. The test is carried out on a CHARPY sample.
The energy absorbed during the test is checked. The value stands for the impact strength of the material (resilience) are Cast iron frame, Pendulum with hardened knife, Brake device to stop the pendulum, Impact energy 300J with 2J graduation, Falling angle: 140°, Pendulum mass kg 21.3, Impact speed: 5.187 m/s.

 

 

(b) IZOD impact testing machine.

The IZOD impact test is an ASTM (American Society for Testing and Materials) standardized method used to determine the impact resistance, or toughness, of a material. When designing a structure or part, it is important for engineers to know the toughness of a material to ensure that their designs not only satisfy the intended application, but are also safe, resilient, and long-lasting. To determine impact resistance (toughness) using an IZOD impact test, a weighted pendulum is dropped from a prescribed height and strikes a notched test specimen. When the specimen breaks, the energy absorbed and the material’s impact resistance can be related back to the potential energy of the pendulum before it is released.

 

 

3. Universal testing machine.

A universal testing machine (UTM), also known as a universal tester, materials testing machine or materials test frame, is used to test the tensile strength and compressive strength of materials. An earlier name for a tensile testing machine is a tensometer. The "universal" part of the name reflects that it can perform many standard tensile and compression tests on materials, components, and structures (in other words, that it is versatile). Common components include. (a) Load frame - Usually consisting of two strong supports for the machine. Some small machines have a single support. (b)Load cell - A force transducer or other means of measuring the load is required. Periodic calibration is usually required by governing regulations or quality system. (c) Cross head - A movable cross head (crosshead) is controlled to move up or down. Usually this is at a constant speed: sometimes called a constant rate of extension (CRE) machine. Some machines can program the crosshead speed or conduct cyclical testing, testing at constant force, testing at constant deformation, etc. Electromechanical, servo-hydraulic, linear drive and resonance drive are used. (d)Means of measuring extension or deformation - Many tests require a measure of the response of the test specimen to the movement of the cross head. Extensometers are sometimes used. (e)Output device - A means of providing the test result is needed. Some older machines have dial or digital displays and chart recorders. Many newer machines have a computer interface for analysis and printing. (f) Conditioning - Many tests require controlled conditioning (temperature, humidity, pressure, etc.). The machine can be in a controlled room or a special environmental chamber can be placed around the test specimen for the test. (g) Test fixtures, specimen holding jaws, and related sample making equipment are called for in many test methods.

 

4. Strain gauge apparatus.

A strain gauge is an electrical sensor; they are used to measure and monitor strain. They are sometimes used as part of different sensors; load cells, pressure transducers and others. The resistance of a strain gauge changes when force is applied and this change will give a different electrical output. Strain gauges use this method to measure pressure, force, weight and tension. When external forces are applied to a stationary object there are two forces present; stress and strain. Stress is the resisting force of the object (like a pushback) strain is the displacement and deformation of the object and this is the force which can be measured by a strain gauge. Because they are small and highly sensitive strain gauges can measure the contraction or expansion of an object even if it is just a small amount when they are correctly bonded to an object or device. Strain gauges are very thin and come in a wide range of shapes and sizes making them suitable for a variety of applications.