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Test methods for adhesives and bonding


There are many reasons are the need for adhesives and bonding tests, some of which are:

(1) Performance Comparison (tensile, shear, peel, flexural, impact, and cleavage strength; durability, fatigue resistance, the environment and conductivity, etc.).

(2) to each batch of adhesive quality checks carried out to determine whether the standards.

(3) test the effectiveness of the surface of their treatment.

(4) to determine useful to predict the performance parameters (curing conditions, dry conditions, layer thickness, etc.).


Test for the material science and engineering are very important in all aspects, especially for adhesives become more important. Test not only their own determination of adhesive strength, but also the evaluation of bonding techniques, surface cleaning, surface treatment effectiveness, surface corrosion, adhesive coating, adhesive layer thickness and curing conditions of the people are very concerned about the issue.


This chapter begins by a general discussion of various types of adhesive joints test, but including some of the more important test, and then in some subject areas are listed in the ASTM methods and practices, as well as SAE Space Agency recommended methods (ARP / s) . Two tensile load of a simple tensile test is the plane perpendicular to the layer through the adhesive surface-center study. ASTM D897 tensile strength of adhesive joints in the ASTM test method is to retain the adhesive in one of the oldest methods.


For the test specimens and fixtures used in the production must be given attention, due to improper design, testing will have the edge when the stress, there is a great stress concentration, stress data obtained by analogy order to balance the different areas or different bonding configuration of connectors The strength is likely to be untrue. Therefore, D897 has been D2095 (bar and round bar specimen tensile strength test methods) replaced. This test piece in accordance with ASTM D2094 (Adhesive trial bar and round bar specimen preparation) standard production, it is easy to adjust the concentricity. If properly produced and tested specimens will be able to more accurately determine tensile bond strength.


Adhesive tensile test was to evaluate the most common test, although there is a connector designed for experienced personnel, there is no guarantee tensile loading in strict form. Most of the structural materials of high tensile strength than the adhesive. One of the advantages is the tensile test to get the most basic data, such as tensile strain, elastic modulus and tensile strength.


California Institute of Technology Weiqian Adams and his colleagues stress distribution on the tensile test were analyzed and found that except when the adhesive material and being viscous modulus match, the stress inside the specimen in the whole distribution is uneven. This difference in modulus caused by transfer of shear stress along the interface. 3 simple shear parallel to the shear stress is the stress generated by surface adhesion. Single-lap shear specimen can not represent the cut, but very practical, making relatively simple, the measured data have practical value, and good reproducibility.


Shear test is a very common test (compared to the following several trials), because of its easy preparation of specimens, and the geometry and operating conditions for many structural adhesive thinner apply. And tensile tests, shear tests are also non-uniform stress distribution, failure stress is based on conventional methods of bonding area is derived by dividing the load, layer inside to withstand the maximum stress was much higher than the average stress, layer be different from the stress and pure shear. Bonding of the "Cut" the destruction of joints form and layer thickness and the stiffness of the material is sticky, sometimes to the main shear failure, and sometimes dominated by tensile failure. Currently used by the shear test method , In addition to ASTM D1002, there are ASTM D3163, compared with ASTM D1002, almost the same configuration, but different thickness. This method is easy to solve the adhesive squeezed out from the edge of the problem.


 ASTM D3165 (laminated composite adhesive lap shear strength test their methods) explains how to prepare the specimen to determine the tensile shear strength of sandwich structures. Double-lap shear test of the standard ASTM D3528 (dual-lap adhesive joint tensile shear strength test methods), the advantage of a more balanced force, thus reducing the single-lap test of splitting and peeling stress stress. But it has also brought new problems, test two or more of the adhesive layer at the same time force, comparison tests may be complicated. Compression and shear tests are usually used, ASTM D2182 ([url = javascript:;] metal [/ url] on the metal bonding shear strength determination of compression method) of the test piece and the lap shear and compression shear tests of similarity devices are described.


ASTM D905 (Adhesive joint compression and shear strength testing method) is to measure the timber (hardwood, etc.) shear strength tests. ASTM E229 is the determination to reverse the shear strength and shear modulus to reverse the experiment. If the test piece fit, and the loading time concentricity good, E229 middle * in the lap shear test than the more uniform stress distribution. 4 Peel peel test for the determination of flexible adhesive to withstand the capacity of local stress concentration. Peel strength was considered to be acting on a line, that is, the force lines. The more viscous material is a soft, adhesive modulus, the higher the surface tends to force the greater the force lines, so the stress is enormous. As the force size is dependent on the sticky material and the adhesive thickness and modulus, it is difficult to estiyoga mate, it is generally believed that the role of stress and failure stress is the line of force, that is, N / cm (N / cm). For the sheet metal is widely used in the more viscous material is a T-peel test (ASTM D1876). In such a test load of all the passed joints, so the measured peel strength than other forms of peel test are low. Elastomer adhesive peel strength with the layer thickness, with the layer thickness, adhesive because of its elastic deformation, leaving an area of increased adhesion, the joint force at the same time, the tensile stress distribution on the width and degree of stress concentration is also small, it should also peel strength is relatively higher.


 T-peel test is a frequently used test method. This test is mainly determined by two kinds of flexible adhesive material bonding joints of the spin-off resistance. The specimen width 25.4mm, thickness of typically 0.5mm, length 304.8mm, was sticky part of the length is only 228.6mm. "Bell" peel test is a test piece in the 25.4mm steel roller with a fixed radius of stripping, the sample from a thin metal sheet (thickness of about 0.635mm) with another in the test does not produce plastic deforyoga mation of metal sheet (thickness of 1.6mm) bond is made with T-peel angle is slightly different, the measured values than the slightly higher T-peel test, test good reproducibility. ASTM D1781 is a metal on metal climbing drum peel test method to 100mm diameter rotating drum to be spin-off of fixed radius. Bell test and climbing drum test devices are used to stabilize the spin-off angle, but the spin-off radius of the fixed method, and can not guarantee the fixed value of spin-off radius, because of its high modulus of metal and steel drum roller or a close played a role with the resistance. In both methods, there are huge energy consumption of the metal deformation, so for certain amount of adhesive is concerned, they are measured peel strength is higher than T-peel test. ASTM D3167 is to determine the adhesive floating roller peel strength tests.


The specimen was sticky from flexible material and rigid has been made sticky bonding material applied to the determination of deflection and a half could be sticky material veneer bonding on hard substrates on the peel strength. This method of inspection and process control is particularly useful, can be used as ASTM D1781 (climbing drum test) Another method of providing an alternative. This method is due to spin-off angle is big, so the operation more stringent. ASTM D903 is the adhesive peel joints or tear strength determination method, which is a standard peel test 1800, was one of the sticky material should have sufficient flexibility to enable it to collapse. Measured from the more rigid substrate (such as the considerable thickness of the metal, plastic , glass, wood, etc.) under the flexible strip of foil, film or tape.


This method is mainly used to measure the adhesive tape, as well as rubber, textile, film and other flexible or soft material attached to the rigid material is sticky on the peel strength. 5 split lines are split and peel force, undermining the beginning from the end. If the sticky material is thick enough, greater rigidity, load acting on the specimen at one end, and with the adhesive surface vertically, was sticky material does not appear to yield deforyoga mation, joint destruction is sudden, that is split. ASTM D3807 describes for engineering plastic adhesive the determination of the adhesive strip method of splitting. 6 creep bonding structure in the use of persistent load to bear, especially the existence of vibration, creep-resistant adhesive is very important. ASTM standards are two methods is to measure the creep. ASTM D2293 is a metal to metal bonding compression and shear creep properties determination method, and ASTM D2294 is a metal to metal bonding tensile creep properties of shear determination method.


 ASTM D1780 is a standard practice to conduct creep tests, which is a common test method, for a single-lap specimen to impose a constant load, with a microscope to monitor the edge layer of fine engraved lines, note the changes over time deformation. As the creep affected by the temperature measured at constant temperature when you must be under. 7 Although the static fatigue strength test application of choice for many bonding adhesive is useful, but does not include the role of stress-intermittent harsh conditions, that is fatigue. The so-called lighting joint fatigue is due to the constant cycle of alternating stress the role of Er Shi joint strength will continue to decline with time until the damage occurring phenomenon. When using the connector to withstand major shocks seem to fatigue the most sensitive. Therefore, the actual components used in an adhesive joint with the previously measured the fatigue strength under simulated conditions of use is very necessary.


ASTM D3166 (Adhesive tensile shear fatigue performance measurement methods), although for metal on metal joints, but is sticky plastic material is also available. All test items are classified as ASTM D1002 single-lap shear joints form of a dedicated test was carried out on tensile test machine, this test function to impose periodic or sine wave-type load. Usually as high as 1800 weeks / min or higher state of fatigue test, recording alternating stress in the maximum stress S, in order to place the alternating cycle of destruction of the logarithm of the number of N mapping can be obtained joints SN fatigue curve, This is also the most commonly used method.


8 shock impact test is mainly used to determine adhesive toughness, that is to determine the adhesive in an instant ability to buffer or absorb external force. Fundamentally speaking, these experiments are measured adhesive on the loading rate sensitivity. ASTM D950 (the impact strength of adhesive joint test methods) shows the specimen under shear when the pendulum impact test method. The results based on specimens subject to impact damage when the role of adhesion per unit area of energy absorbed (KJ/m2) expressed in. Some testing machine is used to accelerate the impact of gravity method, using a series of free-fall into the weight of the specimen, the damage at this time is equal to the weight multiplied by the height of the drop load. Other advanced equipment is the use of compressed air, so that load of time to the 10-5s.


9 Durability many ASTM test and practice the durability of the specimen can be measured, but the most important of which is the wedge test. ASTM D3762 describes the test piece of aluminum flat then layer embedded in a wedge, thus causing the crack tip zone, resulting in tensile stress. Will be followed by the power of the specimen exposed to hot and humid environment, or other required environment. Then calculated the growth of cracks over time and determine damage type. The pilot is essentially quantitative, but the surface was sticky material parameters and adhesive environmental durability should be treated differently