What are the testing methods for the mechanical properties of materials?

Mechanical properties of materials, also known as mechanical performance, refer to how a material deforms when subjected to force. When deformation reaches a certain level, the material fractures.

This behavior of deformation and fracture under external loading is known as mechanical behavior. It is determined by the internal material structure and is an inherent property of the material.

1. Tensile Test

Tensile testing is one of the most commonly used testing methods to determine the behavior of a specimen when subjected to axial tensile loads.

These tests can be conducted at room temperature or under controlled (heating or cooling) conditions to determine the tensile properties of materials.

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

Testing Instruments: Universal testing machines, high-speed testing machines, etc.

Figure 1: Universal Testing Machine

Some Test Standards:

ASTM D3039-76 for determining the in-plane tensile properties of polymer matrix composite materials reinforced with high-modulus fibers.
ASTM D638 for determining the tensile strength and tensile modulus of specimens.

2. Compression Test

Compression testing is a commonly used method to determine the compressive load or compressive resistance of materials. It is also used to measure the recovery capability of materials after being subjected to a specific compressive load for a set period. Compression tests measure the behavior of materials under loading and determine the maximum stress a material can endure under constant or increasing load over time.

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

Testing Instruments: Universal testing machines, high-speed testing machines, compression testing machines, etc.

Figure 2: Diagram of Common Compression Testing Devices

Precautions:

Compression tests are mainly suitable for brittle materials, such as cast iron, bearing alloys, and construction materials.
For plastic materials, the compression strength limit cannot be measured, but the elastic modulus, proportional limit, and yield strength can be measured.

Some Test Standards:

ASTM D3410-75 (Shear Load Method for Determining the Compression Properties of Polymer Matrix Composite Materials with Unsupported Standard Sections)

3. Bending Test

One of the basic methods for testing the mechanical properties of materials, used to determine the mechanical properties of materials under bending loads.

Applicable Materials:

A variety of different materials, including metals, plastics, wood, laminates, particleboard, plaster walls, tiles, and glass.

Figure 3: Three-Point Bending Test Diagram

Testing Instruments:

Universal testing machines, high-speed testing machines

Application Scope:

Mainly includes three-point bending and four-point bending load methods to:

Determine the bending strength of gray cast iron
Determine the bending strength of hard alloys
Measure the bending strength of ceramic materials, tool steels
Inspect and compare the quality and performance of surface heat treatment layers
Test the performance of materials under bending load

Some Test Standards:

ASTM D7624 for determining the flexural stiffness and strength properties of polymer matrix composite materials

4. Shear Test

Shear strength is the ability of a material to withstand shear forces, defined as the strength limit when external forces act perpendicularly to the material axis, causing shearing action.

Applicable Materials:

Various materials, polymers, composites, metals, wood, ceramics, glass, etc.

Testing Instruments:

Universal testing machines, micro-strength testing machines, etc.

Figure 4: Schematic Diagram of the Model State at the End of the Shear Test

Operation Method:

Remove the bending and compression fixtures from the universal testing machine, install the shear fixtures, select the shear test standard in the testing software, and operate as in the bending test.

Some Test Standards:

ASTM D5379 applicable to most fiber-reinforced composite materials.

5. Impact Test

Impact testing is generally used to determine the safety, reliability, and effectiveness of military and civilian equipment when subjected to external forces or impacts.

Applicable Materials:

Various materials, polymers, composites, metals, wood, ceramics, glass, textiles, etc.

Testing Instruments:

Impact testing machines (pendulum and drop-weight types): manual impact testing machines, semi-automatic impact testing machines, fully automatic impact testing machines.

Common Technical Indicators:

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

Some Test Standards:

ISO 179-1-2010 Plastics - Determination of Charpy impact properties
BS EN 950-1999 Door leaves - Determination of the resistance to hard body impact
DIN ISO 2747-1999 Vitreous and porcelain enamels - Determination of resistance to thermal shock of enamelled cooking utensils
BS EN ISO 6603-1-2000 Plastics - Determination of puncture impact behavior of rigid plastics

6. Fatigue Test

Fatigue testing is used to determine the process of fatigue stress or strain cycles in materials or structures.

Fatigue refers to the localized, permanent damage accumulation at a point in a material under cyclic loading conditions.

Applicable Materials:

Various materials, including polymers, composites, metals, etc.

Testing Instruments:

Electro-hydraulic servo fatigue testing machines, etc.

Some Test Standards:

ISO 12108 Metal Materials - Fatigue Testing - Crack Growth Method
ASTM E2207-02 Standard Practice for Axial-Torsional Fatigue Testing of Thin-Walled Tubes with Control of Mean and Alternating Strain
ASTM E1949-03 Standard Test Method for Room-Temperature Fatigue Life of Bonded Metal Strain Gages