Test methods adhesive joints

ASTM D 896-84, Standard Test Method for Resistance of Adhesive Bonds to Chemical Reagents, specifies the testing of adhesive joints for resistance to solvents and... 

Nondestructive Testing of Adhesive Joints. Many commercially available adhesives are based on polymers. NDT of adhesive joints (180) poses challenges because of (2) the small size of possibly deleterious defects (eg, porosity), (2) the thinness of the adhesive layers, and (3) sometimes, the size, shape, and material of the adherends. Acousto-ultrasonics (181) and various types of ultrasonics (182,183) are applicable to adhesive joints. Ultrasonics can be combined with noncontact optical methods (184) and pulsed thermography (185). However, the assessment of the quality or of the quantitative strength of the adhesive bond based on the NDT data often proves difficult. 

The present work was done with the aim to evaluate the efficiency of the acoustic emission method as a diagnostic tool for analysing a carbon plastic composite and its adhesive joints. The samples of the carbon plastic type UKN-5000 were used in the test. Non-defected samples and samples with artificial defects were tested. 

By working trough the method of the AE diagnostics, and as it was with carbon plastic case, the adhesive joint were tested by the step- and two-multiple loading. 

Thus, carrying out tests of the samples shows that the acoustic emission method is quite effective at the quality estimation of carbon plastic and its adhesive joints. Depending on the chosen diagnostic diagram of the construction material loading, the criteria parameters are K, S or AS (a C). 

Munns, G.A. Georgiou, Non-destructive testing methods for adhesively bonded joint nspection - a review, INSIGHT, Vol 37, No 12, Dec 1995, pp 941-952... 

Fig. 1, Schematic of commonly u.sed methods for testing the strength of adhesive joints, (a) Peel test. Note that the peel angle can be changed depending on the test requirements, (b) Double overlap shear test. In this test, the failure is predominantly mode II. (c) Single overlap shear test. In this test the failure mode is mixture of mode I and mode II. (d) Blister test.

In applications where possible degrading elements exist, candidate adhesives must be tested under simulated service conditions. Standard lap shear tests, such as ASTM D1002, which use a single rate of loading and a standard laboratory environment, do not yield optimal information on the service life of the joint. Important information such as the maximum load that the adhesive joint will withstand for extended periods and the degrading effects of various chemical environments are addressed by several test methods. Table 15.2 lists common ASTM environmental tests that are often reported in the literature. 

In addition to tests performed on the incoming materials, test specimens may be made to verify the strength of the adhesive joint. The quality control tests should be those that can quickly and accurately detect deficiencies in the adhesive s physical or chemical properties. ASTM lists various test methods that are commonly used for adhesive acceptance. 

The specification writer must try to put into the specification the requirements that, if met, will provide the greatest likelihood of success. These requirements should be standard tests and acceptable test limits that are agreed upon by both the supplier and the user. The tests should be indicative of how the adhesive is used in production and how the finished joint is to be used in service. Tests that are not directly applicable to the specific application should not be included. Tests should not be used simply because they are standard test methods or have been used in the past. 

ASTM D 1144 provides a recommended practice for determining the rate of bond strength development for either tensile or lap shear specimens. However, peel and can-teliever tests can also be used effectively. Measured bond strength values of partially cured test specimens are compared with those of a reference (i.e., fully cured adhesive joint) to assess the extent of cure. This method may suit some applications, but it is limited in accuracy because it does not directly measure the degree of cure in the adhesive, and the effect on the joint design and substrates may override the effect of cure development. 

Dielectric test methods are used to measure the cure of epoxy adhesives between two conducting electrodes. This method is especially appropriate for metal-to-metal joints because the substrates themselves can be used as the electrode. The adhesive is treated as a capacitor during the test. Its response (dielectric constant, dissipation factor, etc.) over a range of electrical frequencies is measured as a function of curing time. 

There are several ways that actual joints can be tested. For quality control purposes, a proof test is commonly used, as described above. This test imposes a stress on the specimen but limits it to a point well below where any destruction of the joint can occur. This type of test only looks for serious flaws in the bonding processes such as interface contamination, air entrapment in the joint, or undercured adhesive. The prototype joints can also be tested to destruction by using similar test methods described above for standardized testing. This, however, is generally not done at great frequency because of the cost. Generally, most actual joint tests are performed to ascertain the cause of failure (i.e., forensic analysis of the failed joint) or for nondestructive determination of the adequacy of the bond. 

D 2919 Test Method for Determining Durability of Adhesive Joints Stressed in Shear... 

Shear Sandwich Joints in Shear by Tension Loading D 3165 Test Method for Strength Properties of Adhesives in Shear by Tension Loading... 

D 4502 Test Method for Heat and Moisture Resistance of Wood Adhesives Joints... 

D 5041 Test Method for Fracture Strength in Cleavage of Adhesives in Bonded Joints... 

Test Method for Adhesion and Cohesion of Elastomeric Joint Sealants Under Cyclic Movement (Hockman Cycle)... 

Test Method for Adhesion in Peel of Elastomeric Joint Sealants Recommended Practice for Surface Preparation of Concrete for Application of Chemical Resistance Resin Monolithic Surfaces Method of Testing Release Papers Used with Preformed Tape Sealants Test Method for T-Peel Strength of Hot Applied Sealants Test Method for Tensile Adhesive Strength of Preformed Tape Sealants by Disk Method... 

Whilst test methods to measure the mode I fracture resistance of polymer fibre-composites [1] and stmctural adhesive joints [2,3] have now proceeded to full standards, the efforts to standardise a mode II method have been beset by a number of problems. Firstly, there exist a number of competing tests e.g. the end-loaded split (ELS), the end-notched flexure (ENF), the four point end-notched flexure (4-ENF) and the stabilised end-notched flexure (S-ENF) have all been proposed and have been subjected to various inter-laboratory evaluations. However, the results of these programmes have always revealed a very large scatter in the values of Gnc measured e.g, [4], and this scatter has been variously attributed to friction... 

It is my great pleasure to introduce the proceedings of the ESIS TC4 conference, Fracture of Polymers, Composites and Adhesives , which was held in the mountain resort of Les Diablerets, Switzerland between 15-18 September 2002. This was the third conference organised by TC4 and, as on the two previous occasions, it reflects the main activities of the committee which are focussed on developing fracture mechanics test methods for polymers, adhesive joints and composites. 

The adhesion of asphalt to the mineral aggregate is a fundamental property of road asphalt. Once the adhesion deteriorates, the surface becomes unstable and unusable. There is a test method (ASTM D-1191) designed for use on crack and joint sealers that is used primarily to determine whether a jointing material possesses an arbitrary amount of bonding strength at low temperatures where portland cement concrete is being used. 

The most important tests on bonded joints are targeted at the determination of the strength under precisely defined conditions. In order to obtain comparable results from such tests on different test stations, for example, at the adhesive manufacturer and the adhesive user, the test conditions have to be stipulated in detail and must be binding. For this purpose, test standards have been issued by the German Institute for Standardization (DIN) and the European Standards (EN) in cooperation with interested technical groups. The standards for tests in the held of adhesive technology, for example, contain indications regarding material and dimensions of test pieces, the test method to be applied (test equipment, test speed), if required even surface pretreatment of test pieces and other test criteria to be taken into account. 

D 1002 Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to Metal)... 

The fracture-based approach derives from continuum fracture mechanics theory, which claims the strength of most real solids is governed by flaws within the material [2]. To help predict this type of behavior, many test methods have been developed to determine fracture properties of adhesives. These tests are used to characterize the mode I, II, and III fracture properties of many types of material systems. In this study, the focus will be on the mode I and II characteristics of bonded joints for automotive applications. 

Blackman, B. R. K. and Kinloch, A. J., "Fracture Tests for Structural Adhesive Joints, in Fracture Mechanics Testing Methods for Polymers," Adhesives and Composites, A. Pavan, D. R. Moore, and J. G. Williams, Eds., Elsevier, Amsterdam, 2001, pp. 225-267. 

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