Destructive adhesion tests

Non-destructive adhesion testing of plasma-sprayed coatings using ultrasounds and laser shocks, in Thermal Spray 2004 Advances in Technology and Applications, Proceeding of the ITSC, Osaka, Japan, May 10-12, 2004 (eds C.C. Berndt, K.A. Khor, and E. Lugscheider) ASM International. 

In destructive adhesion tests, this latter term may be higher than the thermodynamic work of adhesion. However, small changes in the thermodynamic work of adhesion may result in large changes in the total (real) work of adhesion, thus both terms are of great... 

Non-destructive adhesion test (adhesion) See Adhesion test, non-destructive. 

Mealiness in apples results from a breakdown in adhesion between cells so that chewing the apple tissue results in cell separation rather than cell rupture. Eating a mealy apple is therefore associated with the unpleasant sensory perception of a lack of juiciness, loss of crispness and hardness. A number of studies have succeeded in correlating the degree of mealiness with destructive reference tests such as the Magness-Taylor firmness and confined compression juiciness, but clearly there is a need for non-destructive, on-line detection of mealiness in apples. 

There have been a number of previous attempts to relate the appearance of higher harmonics in the transmission of ultrasound through bonded structures to the quahty of the bonds [2-9]. Commonly used is the so-called nonhnearity parameter y 2, a measure of the generation of only the second harmonic [2], and the distortion factor K which describes the complete nonlinear content of the response [7]. In this paper cahbrated measurements on samples consisting of two aluminum plates joined together by a thin epoxy layer are presented and discussed. The amphtudes and phases of the ultrasonic waves transmitted through the bond are considered. The measurements are related to the results of destructive tensile tests of the adhesive layer. 

After the adhesive is cured, the joint area can be inspected to detect gross flaws or defects. This inspection procedure can be either destructive or non-destructive, as discussed in Section 12.1. Destructive testing generally involves placing samples of the production run in simulated or accelerated service and determining if it has properties similar to a specimen that is known to have a good bond and adequate service performance. The causes and remedies for a number of faults revealed by such mechanical tests are described in Table 12.1. Most of the destructive (mechanical) tests that can be carried out on adhesive bonds are listed in Section 12.2.1.1 (ASTM methods for mechanical properties). Non-destructive tests are far more economical, and every assembly can be tested, if desirable. ... 

One of the more weird adhesion tests is the Mattox bad breath test . In this test, a person breathes on the film to condense moisture. If the film has a high residual stress, the moisture accelerates fracture propagation. When the film fails it blisters or flakes. Obviously, the uninformed individual attributes the failure to the bad breath of the tester. This test has the advantage that it can be done immediately and without equipment. If the film cannot pass this test it will probably fail in the future. The condensing breath often contaminates the film surface for further use and the test could probably be improved to be non-destructive. 

Adhesion test, non-destructive A test that can be performed to establish the presence of a specified amount of adhesion without destroying the film. Examples Tape test of a mirror surface pull-to-limit wire-bond test. 

Adhesion test, tape A comparative go or no-go (pass or fail) adhesion test in which an adhesive tape is applied to the surface of a film and pulled. Usually the him is scored under the area of the test so that the tape pulls on a free edge of the him. If the him remains on the surface, the adhesion is deemed good. May be used as a non-destruchve adhesion test. The tape can be examined for Pull-outs. See also Non-destructive test. 

By testing the adhesive joints for the shift, the loading curve appears to be almost linear until the destruction point. The acoustic noise curves for the weak samples are describing an increased activity at tbe initial loading moment, and just before tbe destruction. The strong samples are acoustically little active up to the start of the macro-destruction. 

The test with the step loading shows that acoustic activity of the solid adhesive joints in the tested carbon plastic is quite low. The maximum on the endurance area was fixed at the predestructive moment. The last is evidence to the fact that the prevailing defect of the adhesive joints is starting its development at the loading level, which is close to the destruction point. 

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... 

The surface forces apparatus (Section 2.3) enables the estimation of a surface energy term, Fq (Eq. 9), providing sufficiently smooth surfaces can be produced. In recent years Chaudhury, Pocius and colleagues have made a valuable contribution to the field of adhesion by developing the technique to study energies of adhesion and of surface energies of polymers [81-85]. These SFA results provide alternatives to values based on traditional destructive tests or contact angle measurements. 

There is no single test that will give a quantitative assessment of adhesion, and those which have been proposed all cause destruction of the test piece. It has already been stated that this property is dependent upon mechanical and chemical bonds between the enamel and the metal. One must, however, also consider the stresses set up at the interface and within the glass itself during cooling after fusion or after a delayed length of time. 

Impact tests Such tests reveal the resistance of coatings to deformation and destruction by concentrated sudden stresses. They thus throw considerable light on the integrity of the metal-coating bond. Changes in adhesion through chemical reaction at the paint/metal interface will be reflected in the impact-test values. 

Loss of Adhesion When Wet. Many coatings, particularly those applied to a roughened surface, show excellent tensile adhesion to steel but lose this adhesion after exposure to pure water at room or elevated temperatures. A thin film of water at the interface is apparently responsible for the loss of adhesion. If the coating is allowed to dry without destructively testing the adhesion, the dried coating often exhibits the original tensile adhesion. The phenomenon is... 

The best approach to achieving good performance in bonded joints is to select the proper adhesive, design the joint properly for the specific application, and maintain rigid process control. One disadvantage in the use of adhesives is the absence of good non-destructive tests to determine the strength of adhesive-bonded joints in a wide variety of ord applications... 

Bond Inspection. After the adhesive or sealant is cured, the joint area can be inspected to detect gross flaws or defects. This inspection procedure can be either destructive or nondestructive. The nondestructive type of tests can be visual or use advanced analytical tests. These types of bond inspections are described below. 

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. 

Nondestructive Testing. Nondestructive testing (NDT) is far more economical than destructive test methods, and every assembly can be tested if desired. Several nondestructive test methods are used to check the appearance and quality of structures made with adhesives or sealants. The main methods are simple ones such as visual inspection, tap, proof, and more advanced physical monitoring such as ultrasonic or radiographic inspection. The most difficult defects to find are those related to improper curing and surface treatments. Therefore, great care and control must be exercised in surface preparation procedures and shop cleanliness. 

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