Explorando propriedades mecânicas de materiais sob cargas estáticas

Exploring mechanical properties of materials under static loads

1. Compression Test

1.1 Overview

Compression Testing is a method used to determine the mechanical properties of materials under static axial pressure. It is one of the fundamental techniques for evaluating the mechanical properties of materials.

The test is mainly used to measure the yield strength of metals under uniaxial compression at room temperature and the compressive strength of brittle materials.

Compressibility is defined as the ability of a material to resist deformation and damage under compressive stress.

In engineering, many components are subject to compressive loads, such as columns in large structures, crane supports, and compression bolts in steel rolling mills. Therefore, the raw materials used in these components must undergo compression tests to ensure their suitability.

1.2 Concept

Compressive yield strength: This is the stress at which a metallic material yields during a compression test, characterized by continuous deformation without an increase in strength.

Superior Compressive Yield Strength: This is the highest compressive stress experienced by the specimen before there is a drop in strength due to yielding.

Least compressive yield strength: This is the minimum compressive stress experienced during the yield period, excluding any instantaneous effects.

Tensile Strength: For brittle materials, this is the maximum compressive stress experienced by the specimen during compression to failure.

Compressive Elastic Modulus: This is the ratio of axial compressive stress to axial strain within the range where there is a proportional linear relationship between axial compressive stress and axial strain during testing.

1.3 Test equipment, instruments and samples

Equipment and Instruments: The following equipment and instruments are required for a compression test:

  • A universal testing machine for materials.
  • A Vernier caliper for accurate measurement.

The compression specimens used in the test are generally cylindrical in shape, with circular or square cross sections.

During compression testing, the friction between the two ends of the sample and the indenter of the testing machine can restrict the lateral deformation of the sample. The shorter the specimen, the greater the influence of this restriction. However, if the sample is too long, it can easily result in longitudinal bending and instability.

Torque-Torsion Angle Curve

Step-by-step charging method:

Within the range of elastic cross-section, the sample must be loaded with a minimum of five equal torques.

The torque and corresponding twist angle at each stage must be recorded. The average twist angle increment for each stage should be calculated and the shear modulus (G) should be calculated using the graphical method formula.

(2) Determination of specified non-proportional torsional strength

The torque-torsion angle curve is recorded using an automatic recording method.

The axis of the cross-twist angle of the elastic straight line segment on the curve is extended to point O. The segment OC is intersected and a parallel line CA is drawn from the elastic straight line segment through point C to point A. corresponding torque for point A is Tp.

Shore Hardness Tester

Sample Requirements:

For the sample to be tested, the following requirements must be met:

  • The mass of the sample must be at least 0.1kg and the thickness must generally be greater than 10mm.
  • The sample testing area should be as large as possible.
  • The surface must be free from oxide scale and foreign dirt and must be non-magnetic.

Representation method:

The hardness value is represented as follows:

  • The number before HS indicates the hardness value.
  • The number after HS indicates the type of hardness scale.
    • 45HSC means that the hardness value measured by a type C hardness tester is 45.
    • 45HSD means the hardness value measured by a D-type hardness tester is 45.

Benefits:

  • Simple operation and high efficiency
  • After testing, there is almost no recoil and testing can be carried out on the finished product.

Disadvantages:

  • Low measurement accuracy
  • Poor repeatability
  • Not suitable for testing with high accuracy requirements.

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