Spontaneous Delamination Research Articles

A Thermodynamic Model of the Adhesive Bond

Abstract An adhesive bond is considered as a thermodynamic system in which the properties of components are expressed in relevant thermodynamic terms. Two hypotheses are analysed, (i) that the maximum strength of the bond is achieved when the interfacial energy is a minimum, and (ii) that only those systems which exhibit a true zero-interfacial energy can be considered stable in terms of their durability. Conditions are found expressed by the 'critical energy ratio', αCRIT, under which the thermodynamic work of adhesion becomes negative and, accordingly, the strength of the adhesive bond is zero. Thermodynamic Equilibrium Diagrams are constructed which allow analysis of bond performance in order to determine conditions for maximum strength, zero strength, and the ‘no-bond’ area, indicating zero-strength or spontaneous delamination tendency.

Decohesion of Thin Films From Ceramic Substrates

ABSTRACTDecohesion of thin films from ceramic or semiconductor substrates is strongly influenced by internal stresses in films and stress concentrations from edges or flaws as well as by interfacial fracture energy. Residual stresses can cause spontaneous delamination, splitting and curling of films under tension or delamination, buckling and spal ling of films under residual compression, even with good interfacial bonding. Delamination behavior is considered using simple fracture mechanics models, supplemented with preliminary measurements of interfacial fracture energies. Formation conditions largely control internal stresses in films; whereas fracture energies are dictated by interfacial chemistry and mechanical factors such as plasticity.

Kinetics of the spontaneous peeling of elastomers

The spontaneous delamination of an elastomer strip in contact on a deformable substrate is studied. Theoretically, the system is analysed in terms of the energy balance theory of fracture by the general equation G − w = w · Φ(αθ · Φ), proposed by Maugis and Barquins in 1978, in which G is the strain energy release rate, w the Dupre's energy of adhesion, and Φ a dissipation function characteristic of the viscoelastic material and of the propagation in mode I, only depending on the temperature through the WLF shift factor αθ and on the crack propagation speed ν. It is shown that the knowledge of the function Φ, which represents viscoelastic lossed localized at the crack tip, allows one to predict the kinetics of the spontaneous peeling and the force applied to the system. Experiments realized with two polyurethane strips in adhesive contact, one strip used as substrate being submitted to instantaneous or increasing tensile elongations, verify theoretical predictions with a reproducibility better than 3%.

The effects of shrinkage on interfacial cracking in a bonded laminate

The effects of shrinkage stress on three types of brittle interfacial failure are treated-cleavage delamination measured in peeling tests, shear delamination measured in lap tests and spontaneous delamination under the influence of shrinkage stress alone without the aid of additional forces. Theoretically, the system is analysed in terms of the energy balance theory of fracture, experimental support being derived from tests on a laminate made by bonding together two equal strips of rubber. Results showed that the laminate was weakest in cleavage and that this weakness was accentuated by shrinkage stresses. By contrast, the laminate exhibited more resistance to shear delamination.

Environmental aspects of adhesion and adhesive joint strength

AbstractWe have outlined a theory which considers the durability of adhesive joints in the presence of a hostile environment. The approach is basically the Griffith theory modified for the presence of liquids. Two main conditions for spontaneous delamination of a composite appear to be immiscibility of the liquid in the environment with the members of the composite and complete interaction of the liquid (in a surface‐chemical sense) with one or more members of the composite. In the absence of chemisorption and interdiffusion in an A‐B composite, we find that (σfL/σf)2 = WABL/WAB, where σf is the critical stress to failure, WAB is the work of adhesion, and the superscript L refers to the presence of a liquid phase. When the liquid (L) interacts, in a surface‐chemical sense, with the composite, we have WAB > WABL, and σfL < σf. To illustrate the main features of the theory, composites are prepared whose interfacial tensions have been modified by the presence of an adsorbed monolayer of a fatty acid. In this instance, the interfacial tensions are changed so that WAB ≈ WABL and σfL ≈ σf. The composite then becomes more stable under an applied stress in the presence of an environment of high relative humidity.