The effects of surface pretreatment on the cyclic-fatigue characteristics of bonded aluminium-alloy joints

Accepted versio

A maximum stress at a distance criterion for the prediction of crack propagation in adhesively-bonded joints

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Modelling the fracture behaviour of adhesively-bonded joints as a function of test rate

Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 × 10−6 m/s to 13.5 m/s. Unstable (i.e. stick–slip crack) growth behaviour was observed at test rates between 0.1 m/s and 6 m/s, whilst stable crack growth occurred at both lower and higher rates of loading. The adhesive fracture energy, GIc, was estimated analytically, and the experiments were simulated numerically employing an implicit finite-volume method together with a cohesive-zone model. Good agreement was achieved between the numerical predictions, analytical results and the experimental observations over the entire range of loading rates investigated. The numerical simulations were able very readily to predict the stable crack growth which was observed, at both the slowest and highest rates of loading. However, the unstable crack propagation that was observed could only be predicted accurately when a particular rate-dependent cohesive-zone model was used. This crack-velocity dependency of GIc was also supported by the predictions of an adiabatic thermal-heating model.Deposited by bulk importAM

The fracture behaviour of adhesively-bonded composite joints: Effects of rate of test and mode of loading

AbstractThe present paper discusses the results of an investigation into the effects of test rate and the mode of loading on the fracture energy, Gc, of adhesively-bonded fibre-composite joints. Various carbon-fibre reinforced-polymer (CFRP) matrix composite substrates have been bonded using two different types of automotive structural epoxy-adhesives. They have been tested via loading the bonded joints in mode I (tensile), mode II (in-plane shear) and mixed-mode I/II from slow rates (i.e., of about 10−5m/s) up to relatively high rates of test of about 15m/s. The high-rate tests were photographed using a high-speed digital video camera to record the deformation of the joint and the fracture behaviour. An analysis strategy has been developed for the various modes of loading (i) to account for the observed fracture behaviour, (ii) to circumvent the problems posed by oscillations in the load traces due to the presence of dynamic effects in the faster tests, and (iii) to account for the kinetic energy associated with the moving specimen arms in the faster tests. Based on the analysis strategy developed, the effect of the test rate on the fracture energy, Gc, for the different loading modes for the joints has been ascertained. Furthermore, various different fracture paths were observed in the tests. They were either cohesive, in the adhesive layer, or interlaminar in the composite substrates. The exact fracture path observed was a function of (i) the type of composite substrate, (ii) the type of adhesive, and (iii) the mode of loading employed. However, the nature of the fracture path was found to be quite insensitive to the test rate. Essentially, it was found that joints subjected to mixed-mode I/II loading were more likely to exhibit an interlaminar fracture path in the composite substrates than when loaded in either pure modes I or II. The propensity for a given joint to exhibit such a fracture path via delamination of the composite substrate has been explained by calculating the transverse tensile stresses induced in the loaded composite arms, and comparing this value to the measured transverse tensile strength of the composite. Following this approach, the underlying reasons for the observed fracture path were identified and could be predicted. Also, the proposed scheme provides a route to design against delamination failure occurring in adhesively-bonded fibre-composite test specimens

Influences of non-singular stresses on plane-stress near-tip fields for pressure-sensitive materials and applications to transformation toughened ceramics

In this paper, we investigate the effects of the non-singular stress ( T stress) on the mode I near-tip fields for elastic perfectly plastic pressure-sensitive materials under plane-stress and small-scale yielding conditions. The T stress is the normal stress parallel to the crack faces. The yield criterion for pressure-sensitive materials is described by a linear combination of the effective stress and the hydrostatic stress. Plastic dilatancy is introduced by the normality flow rule. The results of our finite element computations based on a two-parameter boundary layer formulation show that the total angular span of the plastic sectors of the near-tip fields increases with increasing T stress for materials with moderately large pressure sensitivity. The T stress also has significant effects on the sizes and shapes of the plastic zones. The height of the plastic zone increases substantially as the T stress increases, especially for materials with large pressure sensitivity. When the plastic strains are considered to be finite as for transformation toughened ceramics, the results of our finite element computations indicate that the phase transformation zones for strong transformation ceramics with large pressure sensitivity can be approximated by those for elastic-plastic materials with no limit on plastic strains. When the T stress and the stress intensity factor K are prescribed in the two-parameter boundary layer formulation to simulate the crack-tip constraint condition for a single-edge notch bend specimen of zirconia ceramics, our finite element computation shows a spear shape of the phase transformation zone which agrees well with the corresponding experimental observation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42782/1/10704_2004_Article_BF00018779.pd