Fracture Of Adhesive Joints Research Articles

Failure load prediction of structural adhesive joints

The objective of this study was to determine how the fracture of adhesive joints depends on elastic beam parameters describing the adherends and the applied loads. The basic specimen geometry was the cracked lap shear joint constructed of aluminium alloy with various adherend and bondline thicknesses. Loads were applied in different combinations of bending, tension and shear to generate a failure envelope for each adhesive and specimen geometry. It was found that crack propagation for precracked specimens occured at a critical strain energy release rate but was also a function of the GI/GII ratio and the bondline thickness. The experiments also showed that the loads required to propagate a crack in a precracked specimen were always lower than the loads required to break the fillet. Hence, by treating uncracked joints as being cracked, where the fictitious crack tip is assumed to coincide with the location of the fillet, a conservative estimate of the failure load is obtained.

Non-destructive evaluation of materials and structures by the elastic-wave transfer function method

The elastic-wave transfer function method (ETFuM) is a method for comparing the input elastic wave and the output wave from the test specimens, parts or actual structures and for separating and analysing only the information on the condition of the specimen from the transfer function in the frequency domain. In this review, the background theory and application examples of ETFuM are mentioned. The application examples are concentrated on the estimation of adhesive joint fracture strength and medical application to evaluating the artificial hip joint condition.

Interlaminar shear fracture of laminated composites

The interlaminar fracture toughness in mode II and mode III of a number of advanced composites was studied using beam type test specimens and scanning electron microscopy. Special emphasis was placed on elucidating the material aspects of the fracture process and on quantifying the effect of matrix on fracture energy. The fracture energy in mode II was independent of crack extension while that for mode III exhibited a rather probablistic “resistance” behavior that was attributed to the effect of fiber bridging. The initiation fracture energy, considered here the true measure of G IIIC , coincided with G IIC . For either mode, the interlaminar region ahead of the crack tip exhibited considerable plastic deformations, the severity that is believed to control the laminate toughness. The interlaminar fracture energy in shear, hereby denoted as G SC (=G IIC =G IIIC ), was accurately predicted from a straightforward adhesive joint fracture test provided the adhesive thickness coincide with the thickness of the interlaminar resin layer.

Fracture of adhesive joints and laminated composites

AbstractThe mechanisms of resin controlled failure in adhesive joints and composites (delamination and transverse cracking) are examined. An in‐situ failure model based on the fracture mechanics principles is applied here to describe the failure processes involved. The model centers on the crack tip plastic zone developed in the thin resin layer between the fibers or the adherends. The plastic zone in the resin layer is heavily influenced by a dominant slow varying stress distribution, approximated to be r−m/2 dependent with m ≪ 1 (r is the distance from the crack tip). The adhesive or composite fracture toughness G*IC can then be expressed as a function of several resin properties of comparable importance: modulus E, yield stress σy, resin GIC and residual stress. The relative significance of the resin properties on the adhesive or composite fracture is discussed. The effects of temperature, loading rate, and resin toughening on such failure as a result of the corresponding variations in resin properties are also addressed.

An In-Situ Failure Model for Adhesive Joints

Abstract In this paper, a theoretical model based on the fracture mechanics principle is built to describe the in-situ failure process of adhesive joints. The central concept of the model is that the adhesive fracture is controlled by the plastic zone developed at the crack tip. On the basis of an approximate crack tip stress distribution, a quantitative representation is found to relate the adhesive fracture energy G1c(joint) to certain bulk resin properties: fracture toughness G1c(bulk), yield stress σy, and Young's modulus E. It is found that the factor σ y 2/E is sometimes more important than G1c(bulk) in controlling G1c(joint). The in-situ failure model interprets well the temperature and loading rate dependent phenomena of adhesive joint fracture reported in the literature. A correlation between the resin material variables and the adhesive fracture is thus established.

The use of the double torsion test geometry to study the fracture of adhesive joints

The use of the double torsion test geometry to study the fracture of adhesive joints

Mode I and II fracture of adhesive joints

The compliance method is used to determine strain energy release rates in mode I and II fracture of adhesive bonded joints. A strong dependence of the strain energy release rates upon the adhesive thickness is found. Standard compact tension and compact shear specimens are used. It is found that the former are well suited to the investigation of mode I fracture, but that the latter are less well suited to mode II investigations. Attention is focussed on bond failures caused by cracks propagating between an adhesive and an adherend. Experimental and theoretical arguments are combined to determine the critical strain energy release rates at which such failures occur. The critical values are shown to be strongly dependent upon the method of surface preparation as well as upon the physical properties of the materials used.

Fracture of adhesive joints

AbstractThis paper presents some of the important results obtained from a series of studies on cohesive fracture in adhesively bonded joints. Due to the complex nature of the adhesive joint fracture, an accurate and efficient numerical method particularly suitable for the present problem has been developed, based on a hybrid‐stress finite element formulation. Fracture characteristics in adhesively bonded joints are described in terms of local crack‐tip deformation and stress fields in the polymeric adhesive layer. Effects of material properties, joint geometry, and bond‐line thickness on the crack behavior are studied for classical lap‐shear and currently used double‐cantilever‐beam joints. Of particular interest are the crack‐tip stress intensities in the adhesive layer; their values are obtained for several cases of practical importance.

Crack Tip Processes and the Adhesive-Cohesive Transition in the Environmental Fracture of Adhesive Joints

Abstract Following an earlier paper concerning the role of shrinkage stress on the environmental fracture of adhesive joints, further work has been carried out to investigate the factors which control and limit the rate of interfacial crack growth. The fracture surfaces have been examined using scanning electron microscopy and data from bulk epoxy resin specimens has been obtained for comparison with the results from adhesive specimens. This has allowed a model for slow, water induced crack growth to be proposed.

On the Character of Failure of Adhesive Joints Between Two Polymers

Abstract Up to the present there has been discussion of the locus of fracture of adhesive joints, i.e., if it proceeds precisely at the interphase border, or if cohesive fracture in a weak layer of one of the components takes place. There are only a few data available on this point.

The Role of Shrinkage Stresses in the Environmental Fracture of Adhesive Joints

Abstract Slow interfacial crack growth occurs in epoxy-metal joints when loaded in the presence of water. Previous workers have sought to explain this on the basis of thermodynamic arguments, but this leads to inconsistencies with the results from fracture mechanics studies. A mixed mode failure criterion is proposed in this paper where the strain energy release rate contribution from shrinkage stress is included. This is found to give a more consistent model of joint failure.

Failure criterion for the fracture of structural adhesive joints

The long-term strength of stressed, structural adhesive joints, consisting of aluminium alloy substrates bonded with an epoxide adhesive, has been investigated. The applied adhesive fracture energy, G I c , is shown to be linearly dependent upon the logarithmic time-to-failure; the failure time decreases as the value of G I c is increased. The fracture of these joints over eight decades of time is uniquely described by the hypothesis that there is a critical plastic-zone size developed at the crack tip at failure.

Quasi-Static Adhesive Fracture

Abstract The concept of quasi-static crack propagation is used in the present paper to study quantitatively the effects of environmental fluids on fracture in adhesive joints. The mechanisms and mechanics of environmental adhesive fracture under rising loads are discussed. Two types of cracking behaviour were observed. (1) When the dissolution or the “surface energy reduction” mechanism prevailed, the fracture toughness of the adhesive joint in the environment was reduced. (2) However, when environment-enhanced crazes were formed in the adherend at the crack tip region, the local fracture toughness of the adhesive joint would be increased. But cracking was usually unstable so that crack velocities were not readily measurable. Except in so far as the adhesive surfaces may have considerable effects, the fracture toughness of an adhesive joint is independent of the specimen geometries used in the present work. Also, the variation of fracture toughness with crack velocity for an Aluminum/ Araldite joint in a carbon tetrachloride solution is reported.

Types of fracture of adhesive joints made with polymers

Modern concepts of the fracture of adhesive joints made with polymers are critically analyzed. The results of experiments carried out by new research techniques are used to show that fracture of joints of this kind may be cohesive, adhesive (interfacial), or compound in character.