Adhesives, as one of the most important elements in various industries, play an essential role in the connection and integrity of materials. From the construction and automotive industries to electronics and medicine, choosing the right adhesive and ensuring its quality is of great importance. To ensure the proper performance of adhesives, it is necessary to perform various tests and evaluate them according to specific standards. In this article, we will review different methods of adhesive quality testing and common standards in this field.

The importance of adhesive quality testing

• Performance Assurance: Tests help to ensure that the adhesive has the necessary properties including adhesion, resistance to stress, temperature, and humidity under the intended operating conditions.
• Production quality control: By conducting regular tests, it is possible to ensure the stability of production quality and the absence of defects in adhesives. Periodic tests of adhesives help manufacturers to maintain the quality of their products and prevent possible problems.
• Choosing the right adhesive: tests help to choose the best type of adhesive for a specific application. By performing various tests, it is possible to choose an adhesive that is most compatible with the materials used and environmental conditions.
• Formulation improvement: By analyzing the results of tests, it is possible to improve the formulation of adhesives and optimize their performance.
• Ensuring the optimal performance of the product: low quality adhesives can lead to the separation of parts, reducing the useful life of the product and even accidents.
• Reducing costs: preventing problems caused by the use of low-quality glue and reducing costs related to repairs and reconstruction.
• Increasing the useful life of the product: choosing the right glue increases the durability and longevity of the product.
• Complying with quality standards: compliance of products with national and international standards.

Adhesive quality testing methods

Adhesive testing methods are very diverse and are chosen depending on the type of adhesive, its application and desired standards. Some of the most important testing methods are mentioned below:

• Tensile Test: In this test, a sample of glue that connects two surfaces is stretched at a certain speed to measure the force required to separate the surfaces. or the force required to separate two bonded surfaces is measured. This test is used to determine the adhesion strength.
• Shear Test: In this test, a force is applied parallel to the connection surface to measure the resistance of the adhesive against shear forces. In other words, in this test, the force applied to separate two glued surfaces in the direction parallel to the surface is measured. This test is used to evaluate the adhesive resistance against shear forces.
• Flexural Test: This test is used to evaluate the adhesive resistance against bending forces. The glued sample is subjected to impact to measure its resistance to sudden impacts.
• Adhesion Test: In this test, adhesive adhesion to different surfaces is measured using methods such as tensile, shear or lattice test.
• Fatigue Test: This test is used to evaluate the adhesive behavior under repeated and intermittent loads.
• Thermal Test: This test includes placing adhesive samples at high or low temperatures to evaluate the change in adhesive properties at different temperatures.
• Moisture Resistance Test: In this test, adhesive samples are placed in environments with high humidity to check their resistance to moisture penetration and its effect on adhesion.
• Chemical resistance test: This test is used to evaluate the adhesive’s resistance to contact with different chemicals.
• Ultraviolet (UV) light test: This test is used to check the effect of sunlight on the glue.

Physical tests include tensile test, shear test, bending test, impact test and fatigue test.

Environmental tests include high and low temperature tests, humidity tests, chemical tests, and ultraviolet light (UV) tests.

Common standards related to adhesive quality testing

International standards are used to ensure the integrity and comparability of different test results. Some of the most important standards related to adhesive testing are:

• ASTM International: This organization provides extensive standards for testing various materials, including adhesives. Among them, we can refer to the standards ASTM D4541 (tensile test), ASTM D903 (shear test) and ASTM D3359 (paint adhesion test).
• ISO (International Organization for Standardization): The International Organization for Standardization also has several standards for adhesive testing.
• DIN (Deutsches Institut für Normung): The German Standard Institute also compiles national and international standards in the field of adhesive testing.
• BSI (British Standards Institution): This organization develops British national standards for adhesive testing.

What is the difference between tensile test and adhesive shear test?

In line with adhesive quality testing, tensile test and shear test are two important mechanical tests that are used to evaluate the properties of various materials, including adhesives. Each of these tests provides different information about the material’s resistance to applied forces.

Tensile Test

Purpose: to measure the resistance of a material against the force that tries to stretch and lengthen it.

How to do it: A sample of the material is attached to a tensile testing machine at both ends and then stretched at a certain speed until it breaks.

Measurement parameters

Tensile strength: The maximum force a material can withstand before failure.

Elongation: the amount of elongation of the specimen before failure.

Young’s modulus: indicates the hardness of the material.

Application: To evaluate the resistance of materials against tensile forces such as wires, cables, fibers and some types of adhesives.

Shear Test

Purpose: to measure the resistance of a material against the force that tries to cut it in the direction parallel to the surface.

How to do it: A sample of the material is placed between two plates and then a force is applied parallel to the surface to cut the sample.

Measurement parameters:

Shear strength: the maximum force a material can withstand before shearing.

Application: To evaluate the resistance of materials to shear forces such as adhesives, screws, rivets and mechanical connections.

The main difference between tensile test and shear test

Tensile test: It is used to evaluate the initial adhesion strength and resistance to separating forces.

Shear test: It is used to evaluate the adhesive resistance against sliding and shearing forces, which is more important in many practical applications.

Both tensile and shear tests are necessary to evaluate the mechanical properties of adhesives. Choosing the right test depends on the type of adhesive, the type of surface, the environmental conditions and the final application. By performing these tests, it is possible to ensure that the glue used has the necessary properties to connect the parts reliably and stably.

How to measure the adhesive’s resistance to heat?

Adhesive resistance to heat is one of the most important features that is considered in many industrial and construction applications. Adhesives that are exposed to high heat or temperature changes must be able to maintain their adhesion and prevent degradation. To measure the thermal resistance of glue, different methods are used, each of which is performed according to specific standards and with specific equipment. Below are some of these methods:

Thermal Cycling Test:

The bonded sample is subjected to alternating temperature cycles (eg, from ambient temperature to elevated temperature and then to ambient temperature). In each cycle, the adhesive strength is measured. By repeating these cycles, it is possible to determine the reduction in adhesive strength due to heat and temperature changes.

High Temperature Test:

The glued sample is placed at a high temperature and kept for a certain period of time, and after a certain period of time, the strength of the glue is measured. This test is used to determine the maximum temperature that the adhesive can withstand.

Thermal Shock Test:

The glued sample is quickly moved between two very different temperatures. This test is used to check the adhesive resistance against sudden temperature changes.

Combined Thermal Test:

This adhesive quality test is a combination of the above methods and is used to simulate the actual conditions of adhesive application. For example, the glued sample is exposed to humidity, sunlight and temperature changes.

Factors affecting the choice of test method

Type of glue: each type of glue has its own thermal properties.

Application of glue: working conditions and temperature in which the glue is used.

Target standards: Different standards define specific test methods for different types of adhesives.

Equipment used

Furnace: To create a high and uniform temperature

Freezer: To create a low temperature

Tensile testing device: to measure the strength of the adhesive

Thermometer: to measure temperature

Timer: to control the sample exposure time at different temperatures

Related standards

ASTM: International Organization for Testing and Materials has different standards for thermal testing of adhesives.

ISO: International Organization for Standardization provides international standards for adhesive testing.

Important considerations

Sample preparation: Bonded samples must be prepared in a standardized and careful manner to obtain reliable results.

Reproducibility: Each test should be repeated several times to ensure that the results are reliable.

Interpretation of the results: The results of the tests must be carefully interpreted and evaluated according to the application of the adhesive.

Measuring the thermal resistance of adhesive is an important process to ensure the quality and test the quality of adhesive in various applications. By using appropriate testing methods and accurate equipment, the thermal resistance of the adhesive can be accurately measured and the appropriate adhesive can be selected for each application.

conclusion

Adhesive quality testing is an essential step in the production and use of adhesives. By choosing appropriate test methods and using valid standards, it is possible to ensure the optimal performance of adhesives in various applications. Also, by analyzing the results of the tests, it is possible to improve the formulation of adhesives and develop new products.