Mechanisms of bond failure

Definition of Failure Modes Mechanisms of Bond Failure... 

H. M. Clearfield joined Martin Marietta Laboratories in January, 1985. Since then, he has primarily investigated surface and interfacial phenomena in adhesive bonding, including surface preparation of titanium alloys for structural applications at high service temperatures, mechanisms of bond failures that occur at high temperatures, and bonding of the thermal protection system to the space shuttle external tank. Additionally, he has investigated dopant depth distributions in ion-implanted and laser-annealed silicon. Dr, Clearfield is supervisor of surface analysis facilities at Martin Marietta Laboratories. Recently, Dr. Clearfield joined IBM s T. J. Watson Research Center. 

In many applications rubber is bonded to metal for fixing purposes or in order to alter the stiffness, and the integrity of the bond is often vital for maintenance of the required stiffness characteristics and to ensure adequate life. The mechanics of bond failure were studied for various types of deformation. Provided that the tests were carried out under suitable loading conditions, time-dependent failure with a similar locus was observed in peeling at 90 or 180 degrees, pure shear and various combinations of simple shear and compression. There were indications that an energetics approach could enable results from different geometries to be quantitatively interrelated. Cavitation-... 

An investigation of the mechanism of adhesive failure of polydimethylsiloxane elastomers was conducted [75]. The study showed that the total adhesive failure energy could be decomposed into energies for breaking chemical bonds, breaking physical bonds and deforming the bulk viscoelastic elastomer. 

An understanding of the mechanism of creep failure of polymer fibres is required for the prediction of lifetimes in technical applications. Coleman has formulated a model yielding a relationship similar to Eq. 104. It is based on the theory of absolute reaction rates as developed by Eyring, which has been applied to a rupture process of intermolecular bonds [54]. Zhurkov has formulated a different version of this theory, which is based on chain fracture [55]. In the preceding sections it has been shown that chain fracture is an unlikely cause for breakage of polymer fibres. 

Bartz, W.J. and Xu, Jinfen, Wear Behaviour and Failure Mechanism of Bonded Solid Lubricants, Lubric. Eng., 43, 514, (1987). 

The above discussion indicates that TBCs can fail in a number of locations. Wherever a crack nucleates it will propagate if the stored elastic-strain energy exceeds the fracture toughness in that location. The mechanics of TBC failure have been reviewed in detail. The details of the fracture process depend on the type of bond coat and its fabrication, the technique for depositing the topcoat, and even on the nature of the thermal exposure (e.g., cycle frequency). ... 

Each of the fixation mechanisms has an idiosyncratic behavior, and their load transfer characteristics as well as the failure mechanisms are different. Further complexity arises from prostheses which combine two or more of the fixation mechanisms in different regions of the implant. Multiple mechanisms of fixation are used in an effort to customize load transfer to requirements of different regions of bone in an effort to preserve bone mass. Loosening, unlocking, or de-bonding between implant and bone constitute some of the most important mechanisms of prosthetic failure. 

The advent of high resolution scanning electron microscopy (STEM) represents a tremendous advancement in the microscopic examination of adherend and failure surfaces. Venables et al. (15) have demonstrated using STEM that the degradation mechanism causing bond failure of aluminum alloys in a humid environment is the conversion of the surface oxide with a cellular and whisker structure to a surface hydroxide with a "com flake" type structure. 

The various methods used to study the effect of environmental exposure on structural bonds have been described, pointing out that such methods provide results of a comparative nature only. There are at present few test methods that provide information useful for making predictions of durability of actual bonded structures. Most of the test methods involve the simultaneous effects of an applied load and environmental exposure some involve exposure to cyclic conditions. As explained, these conditions are much more detrimental to joint performance than is exposure to a single test condition. The tests based on fracture mechanics principles have provided some especially useful information and insights into the mechanisms of environmental failure. 

De Lolhs N. Theory of adhesion—Part 2—proposed mechanism for bond failure. AdhesAge 1969 13(l) 25-29. 

De LolUs N. Theory of adhesion—part 2—proposed mechanism fm bond failure. Adhes Age 1969 13(l) 25-9. 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

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