How much do you know about mechanical property tests in the field of materials science?

What is mechanical property test?

Mechanical property testing evaluates the mechanical properties of a material by applying external forces and measuring its stress and strain. Stress refers to the magnitude of the internal force of the material, and strain refers to the deformation of the material under the action of external force. By measuring stress and strain, the strength, stiffness and durability of materials can be determined.

In the field of material science, mechanical property tests are mainly divided into two categories: static properties tests and dynamic property tests. The static properties test mainly studies the static mechanical properties of materials, such as yield strength, tensile strength, elastic modulus, etc., while the dynamic performance test focuses on the dynamic mechanical properties of materials, such as fatigue strength and impact toughness. The wide application of these test methods provides important support for the optimal design of various engineering structures and products.

The most common statics test is tensile test and compression test. The tensile test obtains the tensile strength, yield strength and other indicators of the material by applying tensile force on the specimen to make it plastically deformed until it breaks. The compression test obtains data such as compressive strength and deformation of the material by applying pressure on the specimen to compressive deformation until it ruptures. The acquisition of these test data has important guiding significance for the selection and design of materials.

The most common dynamic performance tests are fatigue tests and impact tests. The fatigue test simulates the behavior of the material during long-term use by cyclically loading the stress on the specimen, so as to obtain data such as the fatigue strength of the material and the fatigue crack growth rate. The impact test simulates the behavior of the material in the impact environment by applying an impact load on the specimen, so as to obtain data such as the impact toughness and energy absorption of the material. These test results are important for evaluating the durability and safety of materials.

When conducting mechanical property tests, the following points need to be paid attention to:

Preparation of specimens: The shape, size and preparation method of the specimen should meet the test requirements to ensure the accuracy and comparability of the test results.

Selection of test equipment: select appropriate test equipment according to test methods and material properties, and ensure the accuracy and reliability of equipment.

Control of test conditions: Environmental conditions, such as temperature, humidity, pressure, etc., should be strictly controlled during the test to ensure the stability and repeatability of test results.

Data analysis methods: correct data processing and analysis of test results, extraction of useful information, and reliable basis for engineering practice.

Mechanical property test generally includes tensile test, impact test, torsion test, compression test, bending test, flattening test, stress relaxation test, hardness test and fatigue test, etc., the material, groove form, welding process, etc. of the welding specimen are the same as the actual situation of the product.

1. Tensile test

Tensile testing is one of the most commonly used test methods to determine the behavior of a specimen after being subjected to axial tensile loads. These test types can be performed at room temperature or under controlled (heating or cooling) conditions to determine the tensile properties of the material. It can be used to measure the tensile strength, yield strength, elongation and end face shrinkage of welded metal and welded joints and other mechanical performance indicators, in the tensile test can find some welding defects at the fracture of the specimen, verify the correctness of the welding material and welding process, tensile test can be made into plate specimens, round specimens or tubular specimens.

Applicable materials:

Metals, plastics, elastomers, paper, composites, rubber, textiles, adhesives, films, etc.

Common tensile test results:

Maximum load: Elongation at maximum load

Maximum load work: stiffness

Breaking load: Deformation at break

Work done by breaking: string slope

Stress: Strain

Test instruments: universal testing machine, high-speed testing machine, etc

2. Impact test

Impact test is also known as impact toughness test, used to determine the impact toughness and gap sensitivity of weld metal and welded joint, from the fracture form can judge their failure properties (plastic fracture or brittle fracture) through low temperature impact test, can also measure the brittle transition temperature of weld metal and welding heat affected zone.

Applicable materials: a variety of materials, polymers, composite materials, metals, wood, ceramics, glass, textiles and so on

Test instruments: impact testing machine (pendulum type and drop weight type) section quasi-measurement and control testing machine: manual impact testing machine, semi-automatic impact testing machine, automatic impact testing machine.

Common technical indicators: peak acceleration, pulse duration, velocity change (half-sine wave, post-peak sawtooth wave, trapezoidal wave) and waveform selection.

Some test criteria:

ISO179-1-2010 Determination of pendulum impact properties of plastics

GB/T15231.5-1994 Performance test method for glass fiber reinforced cement impact resistance

GB/T14152-2001 External impact resistance of thermoplastic pipes

GB/T21239-2007 Test for compression performance of fiber-reinforced plastic laminates after impact

BSEN950-1999 door leaf. Determination of impact resistance to hard objects

DINISO2747-1999 Enamel and enamel. Enamel cooking utensils. Determination of thermal shock resistance

GB/T3917.1-2009 Tearing performance of textile fabrics

BSENISO6603-1-2000 Plastic rigid plastic punching performance determination department quasi-measurement and control testing machine

3. Torsion test

Torsion test is a test to determine the resistance of materials to torque, and is one of the basic test methods for material mechanical property tests. Torsion test can determine the strength and plasticity of brittle and plastic materials, and torsion test is often required for manufacturing parts that are often subjected to torque such as shafts and springs.

Test instrument: torsion testing machine

4. Compression test

The compression test is a test method commonly used to determine the compressive load or compressive resistance of a material, and also to determine the resilience of a material after being subjected to a specific compressive load and holding it for a set period of time. The compression test is used to determine the behavior of a material under loading. In addition, the maximum stress that a material can withstand under (constant or incremental) loads over a period of time can be determined.

Applicable materials:

Metals, plastics, elastomers, paper, composites, rubber, textiles, adhesives, films, etc.

Test instruments: universal testing machine, high-speed testing machine, compression testing machine, etc

5. Bending test

Bending test is also known as cold bending test, is a test method to determine the plasticity of welding joints when bending, but also a method to test surface quality, it is a certain shape and size of the sample, under room temperature conditions is bent to appear the first crack larger than the specified size of the bending angle as an evaluation standard, cold bending test can also reflect the plastic difference in each area of the welded joint, assess the molten core quality of the molten core area and expose welding defects, bending test is divided into positive bending, back bending and side bending three, can be selected according to product technical conditionsIt is easy to find the root defects of the weld, and the side bending can check the bond strength between the weld layer and the weldment.

Suitable materials: many different materials, including metal, plastic, wood, laminate, particleboard, clear water walls, tiles and glass.

Test instruments: universal testing machine, high-speed testing machine

Application range: there are mainly three point bending and four point bending two loading methods,

Determination of the flexural strength of gray cast iron

Determination of the flexural strength of cemented carbide

Measure the flexural strength of ceramic materials and tool steels

Inspect and compare the quality and performance of surface heat treatment layers

Tests the performance of materials under bending loads

Some test criteria:

ASTM Quasi-Measurement and Control Tester D7624 is used to determine the bending stiffness and strength properties of polymer matrix composites

GB/T232-2010 "Bending test methods for metallic materials"

6. Flattening test

Flattening test is a test method used to test the deformation performance of metal pipe flattened to a specified size and show its defects.

When the flattening test is carried out, the specimen is placed between two parallel plates, and the flattening distance specified by the relevant technical conditions is evenly pressed by a press or other method (flattening distance of the outer wall of the tube or the flattening distance of the inner wall, expressed in millimeters), and the bending deformation of the specimen is checked, if there is no crack, crack or weld crack, it is considered qualified.

7. Stress relaxation test

The stress relaxation test is used to determine the creep behavior of a specimen when subjected to tensile or compressive loads for a long time at a constant temperature. The ratio of the deformation rate of the specimen to the stress at a constant temperature is the creep rate. It is calculated from the creep and slope on the timegraph line. Creep usually occurs under elevated temperature conditions, so this type of test is often performed inside a temperature chamber to achieve precise heating/cooling control. Temperature control is essential to minimize the effects of thermal expansion on the sample.

8. Hardness test

The flattening test can be used to determine the plasticity of the tube when the welded joint is flattened, and the plasticity is determined according to the distance between the upper and lower outer walls of the flattened tube when the first crack occurs on the test.

9. Fatigue test

Fatigue test is used to determine the strength of welded joints under alternating load, it is often expressed by the stress and cycle number of fractures under a certain alternating load, fatigue strength test according to different forces, can be divided into tensile fatigue, bending fatigue and impact fatigue test.

Applicable materials: a variety of materials, including polymers, composite materials, metals, etc.

Test instruments: electro-hydraulic servo fatigue testing machine, etc.

In summary, mechanical property testing has an important position in the field of material science. Through in-depth research on the mechanical properties of materials, we can fully understand the mechanical behavior and characteristics of materials, and provide strong support for the optimal design of various engineering structures and products. With the development of science and technology, mechanical property test methods and technologies are also constantly improving and improving, which provides an important guarantee for the continuous deepening of material science research. Therefore, we should fully understand the importance of mechanical property testing and continuously promote its application and development in engineering practice and scientific research.

Enjoy testing can be carried out according to the needs of users for mechanical property test, the test is to use static tensile force on the tensile testing machine to axial tension of the specimen to measure the force and corresponding elongation (generally stretch to fracture), to determine its corresponding mechanical properties of the test.

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