Test Methods For Adhesives And Adhesives

The test can not only measure the strength of adhesives, but also evaluate the problems of bonding technology, surface cleaning, surface treatment effectiveness, surface corrosion, adhesive coating, adhesive thickness and curing conditions.

The tensile test is the test of loading perpendicular to the glue plane and passing through the center of the adhesive face.

The tensile strength test method of ASTM D897 adhesive joints is one of the oldest methods of retaining adhesive in ASTM.

Attention should be paid to the manufacture of test pieces and fixtures. Due to improper design, the edge stress and stress concentration will be generated during the test. The stress data obtained by using the method to calculate the strength of different bonding areas or different structural joints may not be true.

Therefore, D897 has been replaced by D2095 (bar and bar tensile strength test method).

This specimen is made in accordance with the standard of ASTM D2094 (preparation of bar and round bar test in adhesive test), and it is easy to adjust concentricity.

If the specimen is correctly manufactured and tested, the tensile bond strength can be measured more accurately.

Tensile test is the most common test for evaluating adhesives. Although the joints are designed by experienced personnel, it is not guaranteed that the loading is completely tensile.

Most structural materials have higher tensile strength than adhesives.

One of the advantages of tensile test is that it can get the most basic data, such as tensile strain, elastic modulus and tensile strength.

The difference in modulus results in shear stress passing along the interface.

The pure shear stress is the stress generated by the parallel bonding surface.

Single lap shear specimen can not represent shear, but it is very practical and simple to manufacture. The measured data have practical value and good repeatability.

Like the tensile test, the stress distribution of the shear test is also uneven. The failure stress is the normal way to divide the load by the adhesive area. The maximum stress in the adhesive layer is much higher than the average stress. The stress of the adhesive layer is different from that of the pure shear.

The failure mode of the adhesive shear joint is related to the thickness of the adhesive layer and the stiffness of the adhered material. Sometimes the shear failure is the main cause and sometimes the tensile failure is the main cause.

The method solves the problem that the adhesive is easily extruded from the edge.

ASTM D3165 (laminated composite adhesives tensile shear strength test method) shows how to prepare specimens to determine the tensile shear strength of sandwich structures.

The standard of double lap shear test is ASTM D3528 (double lap adhesive joint tensile shear strength test method), the advantage is that the force is more balanced, thus reducing the splitting stress and peel stress of single lap test.

But it also brings new problems. When testing two or more layers of adhesive force at the same time, the comparative test may be complicated.

ASTM D905 (test method for compressive shear strength of adhesive joints) is an experiment for determining shear strength of timber (hardwood, etc.).

ASTM E229 is the test for determining the shear strength and the shear modulus of torsion.

If the specimen is suitable and the concentricity is good when loading, the stress distribution of adhesive layer is even more uniform than that of lap shear test in E229.

The peel test is used to determine the ability of flexible adhesives to withstand local stress concentration.

The stripping force is considered to be acting on a line, that is, the force of the line.

The softer the adhesive is, the higher the adhesive modulus is, and the more the force on the surface is, the greater the stress is.

Because the area of stress depends on the thickness and modulus of the adhesive and adhesive, it is difficult to estimate. Therefore, it is generally considered that the action stress and failure stress are linear forces, namely Newton / centimeter (N/cm).

The T peel test (ASTM D1876) is widely used for sheet metal adhesion.

In this test, the load is all pferred to the joint, so the peel strength is lower than that of other forms of peel test.

T peel test is a frequently used test method.

This test is mainly to measure the resistance of two flexible adhesive joints to peeling.

The specimen is 25.4mm wide, with a thickness of 0.5mm and a length of 304.8mm, and the length of the adhesive part is only 228.6mm.

The "Bell" peeling test is a test piece that is stripped on the steel roller of 25.4mm with a fixed radius. The specimen is bonded by a thin sheet of metal (about 0.635mm thickness) and another metal sheet (thickness of 1.6mm) that does not produce plastic deformation in testing. It is slightly different from the T peel angle. The measured value is slightly higher than that of the T peel test, and the test repeatability is better.

ASTM D1781 is a metal to metal climbing drum stripping test method, with a diameter of 100mm rotary drum to obtain a fixed peel radius.

The device used in Bell test and creeping test is designed to stabilize the stripping angle. However, the method of fixed peeling radius does not guarantee the peeling radius is fixed, because the high modulus metal resists the close coordination with the steel roller or drum.

In these two methods, a large amount of energy is consumed in metal deformation. Therefore, for certain adhesives, the peel strength is higher than that of the T peel test.

The specimen is made of flexible sticky material and rigid adhered material. It is suitable for measuring the peel strength of semi flexural adhered material on hard substrate.

This method is particularly useful for acceptance and process control, and can be used as another alternative method for ASTM D1781 (climbing drum test).

This method is very strict because of the large angle of stripping.

The flexible foil, film or tape is stripped from the harder substrate (such as the thickness of metal, plastic, glass, wood, etc.).

This method is mainly used to measure the peel strength of adhesive tape and elastic or soft material such as rubber, fabric, film and so on.

Splitting and stripping are all forces on the line, and the damage begins at the end.

If the adhered material is thick enough and the rigidity is large, the load will act on one end of the specimen and be perpendicular to the bonding surface, and the adhesive will not yield deformation. The joint failure will happen abruptly, that is, splitting.

ASTM D3807 explains the method for determining the splitting stripping of adhesives for engineering plastics bonding.

Adhesive structure is subjected to sustained load during use, especially in the presence of vibration. The creep resistance of adhesives is very important.

ASTM standard has two ways to measure creep.

ASTM D2293 is a method for measuring the compression shear creep properties of metal to metal bonding, and ASTM D2294 is a method for determining the tensile shear creep properties of metal to metal bonding.

ASTM D1780 is a standard practice for creep test. This is a general test method. For a single lap specimen, a constant load is applied, a microscope is used to monitor the edges of the adhesive layer, and time dependent deformation is recorded.

As creep is affected by temperature, it must be carried out at constant temperature.

Although the static strength test is useful for many adhesive applications, it does not include the harsh condition of stress discontinuity, namely fatigue.

The fatigue of joints is due to the continuous cyclic alternating stress, so that the strength of the joint will continue to descend until the damage occurs with the extension of time.

Joints that suffer great vibration during use seem to be most sensitive to fatigue.

Therefore, it is necessary to determine the fatigue strength under the simulated condition before an adhesive joint is used on the actual component.

ASTM D3166 (bonding tensile shear fatigue test method) is used for metal to metal joints, but also for plastic sticky materials.

All specimens were made of ASTM D1002 single lap shear joint. The test was carried out on a dedicated tensile testing machine, which exerts periodic or sinusoidal loading.

The fatigue test is usually carried out at a height of up to 1800 weeks /min or higher. The maximum stress S in alternating stress is recorded. The S-N fatigue curve of the joint can be obtained by plotting the logarithm of the alternating cycle number N of the failure, which is the most commonly used method.

The impact test is mainly used to determine the toughness of the adhesive, that is, to determine the ability of the adhesive to buffer or absorb the external force at a moment.

Basically, all these tests are sensitive to the loading rate of adhesives.

ASTM D950 (test method for impact strength of adhesive joints) illustrates the pendulum test method for shear specimens subjected to impact force.

The test result is expressed by the absorbed energy (KJ/m2) per unit adhesive area when the specimen is damaged by impact force.

Some test machines use gravity acceleration impact method, and use a series of weights to drop freely to the test piece. At this time, the load is equal to the weight by the falling height.

Other advanced instruments use compressed air to shorten the load time to 10-5s.

Many ASTM tests and practices can measure the durability of specimens, but the most important is the wedge test.

ASTM D3762 introduced a wedge in the plain aluminum specimen adhesive layer, resulting in tensile stress at the crack tip area.

After that, the stressed specimen is exposed to the hot and humid environment or other required environment.

Then the crack growth with time and the type of failure are calculated.

This test is basically quantitative, but the surface treatment parameters of sticky materials and the environmental durability of adhesives should be treated differently.