Relationship between mechanical properties of and crack progogation in epoxy resin adhesives

Gledhill, R. A.; Kinloch, A. J.; Yamini, Salim; Young, Robert J.

doi:10.1016/0032-3861(78)90285-9

Cited by 131 publications

(49 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For the epoxy adhesive, from dynamic mechanical thermal analysis (DMTA) studies, the value of tanδ r at room temperature and a relatively low test frequency of 1 rad/s is 0.014 [16]. From Equation (5) Thus, from (a) the current values of n being very similar as deduced from the fracture tests and the DMTA studies and (b) by analogy to previous work [13][14][15], it appears that the viscoelastic processes which operate in the vicinity of the crack tip control the rate dependence of the toughness, G c , of the present adhesive joints. This explains why no effect of the RH, substrate type or surface pretreatment used is observed with respect to the rate dependence; i.e.…”

Section: The Relationship Between G C and Asupporting

confidence: 56%

“…Previous workers [13][14][15] have found a similar relationship for crack growth in thermoplastic and thermosetting polymers, which is also associated with a relatively low value of n. Williams [14] has postulated that viscoelastic processes occurring at the crack tip control the dependence of G c upon the crack velocity, a  , and that the value of n is related to the polymer's viscoelastic properties by:…”

Section: The Relationship Between G C and Amentioning

confidence: 91%

See 1 more Smart Citation

Crack Growth of Structural Adhesive Joints in Humid Environments

Korenberg¹,

Kinloch²,

Watts

2004

The Journal of Adhesion

View full text Add to dashboard Cite

The adhesive fracture energy, G c , of aluminium-alloy and steel joints, bonded with a rubbertoughened epoxy adhesive, has been measured using monotonically-loaded tests. Such tests have been conducted at different levels of relative humidity and two surface pretreatments have been employed for the substrates prior to bonding: a simple grit-blast and degrease ('GBD') pretreatment or a silane primer ('GBS') pretreatment. When G c was plotted against the crack velocity, three regions of fracture behaviour could be distinguished. At low rates of displacement the crack grew in a stable manner, visually along the interface, and relatively low crack velocities could be readily measured. This was termed 'Region I' and here the value of the adhesive fracture energy was relatively low and decreased steadily as the relative humidity was increased. On the other hand, at relatively high rates of displacement the crack grew in a stick-slip manner mainly cohesively in the adhesive layer at approximately 20 km/minute. This was termed 'Region III', and here the value of G c was relatively high and independent of the relative humidity. In this region the crack was considered to grow faster than the water molecules were able to reach the crack tip, which explains the independence of G c upon the test environment. In between 'Region I' and 'Region III', a transition region was observed which was designated as 'Region II'. The major effect of the 'GBS' pretreatment, compared to the 'GBD' pretreatment, was to increase the value of G c both in 'Regions I and III', although the presence of the silane primer had the greater effect in 'Region I'. INTRODUCTIONThe use of structural adhesives offers many advantages when compared with other more traditional joining methods such as welding, riveting and mechanical fasteners [1]. However, as with any technology, there are some potential disadvantages associated with the use of adhesives.In particular, adhesive joints may suffer environmental attack when exposed to relatively hot and humid environments. The development of a sound accelerated-ageing test method to assess the susceptibility of an adhesive 'system' (i.e. the adhesive/primer (if any)/substrate and substrate surface pretreatment in combination) to such attack would represent a significant advance, especially if such tests could be completed in a relatively short time-scale [2].The aim of a sound and meaningful accelerated ageing test must be to accelerate the mechanisms of attack seen during the service-life of the bonded joint, and not to induce misleading and irrelevant mechanisms. For example, it is well known that to accelerate the rate of environmental attack it is not possible simply to raise the temperature of the environment, since unrealistically high test temperatures will indeed change the mechanisms of attack. One method of accelerating the rate of attack which has recently been explored in detail by Kinloch and coworkers (e.g. [3]) has been the use of cyclic-fatigue tests, using a fracture-mechanics approach, conducte...

show abstract

Section: The Relationship Between G C and Asupporting

confidence: 56%

Section: The Relationship Between G C and Amentioning

confidence: 91%

Crack Growth of Structural Adhesive Joints in Humid Environments

Korenberg¹,

Kinloch²,

Watts

2004

The Journal of Adhesion

View full text Add to dashboard Cite

show abstract

“…The mechanism of plastic void growth in an epoxy matrix has been modeled by Huang and Kinloch, who find that this contribution to the toughness of a rubber-toughened epoxy is negligible at reduced temperatures [75]. As T. of the epoxy was approached, however, the inelastic growth of voids became the major consumer of energy due to the sharp reduction in yield stress.…”

Section: Cavitationmentioning

confidence: 99%

Experimental investigations of crack trapping in brittle heterogeneous solids

Mower

Argon

1995

Mechanics of Materials

View full text Add to dashboard Cite

Over the past two decades many mechanisms of toughening have been considered for brittle solids. Some of the most prominent ones applicable to either monolithic materials or fiberreinforced composites include deformation-induced local transformations, micro-cracking, crack trapping, crack bridging, and fiber pull-out. Few if any of these have been studied in the past in a manner which permitted evaluation of the effects of individual mechanisms in the absence of other interacting mechanisms. Here we present the development, analysis and results of an experimental study of toughening by the process of crack trapping by second-phase particles (spheres and fibers) of such toughness that make them impenetrable by probing cracks, forcing the cracks to bow around the obstacles with increasing applied load.The model fracture specimens employed here were wedge-loaded double cantilever beams cast of a brittle epoxy, containing macroscopic (3mm-diameter) inclusions of Nylon or polycarbonate having similar elastic properties to the matrix. The tests were performed at -60*C to achieve controlled, stable crack propagation. Images of the crack fronts advancing at velocities of about 10-4 M/s were recorded with good resolution, providing a continuous record of crack-front shapes during the evolution of the crack-trapping process from the initial pinning configuration through the transition to crack-flank bridging. Remarkable agreement between these images and crack-front shapes predicted by the numerical simulation of Bower & Ortiz is demonstrated. A parametric approach was adopted to study the influence of obstacle spacing, surface adhesion and thermally-induced residual stresses upon the observed crack-front behavior and enhanced stress intensity required to propagate the cracks past these obstacles. Analysis of the quantitative data has demonstrated that, in brittle matrices containing particle volume fractions of approximately 0.2, toughness enhancement by over a factor of two, relative to neat matrix values, may be achieved through the crack-trapping mechanism alone, provided that a high level of adhesion can be maintained between the matrix and the tough reinforcing particles.

show abstract

“…The epoxy system based on the reaction of the difunctional epoxy monomer diglycidyl ether of bisphenol-A, DGEBA, with aliphatic amines is such an example. The properties of this and other epoxy systems can be varied as a function of the molecular weight of the hardener molecule [7][8][9][10] , by variations in processing conditions [11][12][13] or by the use of different hardener to monomer ratios 8,11,[13][14][15][16][17][18][19][20][21] . This last variable introduces boundary condition (i.e., when a variable like temperature or the amount of monomers is changed).…”

Section: Introductionmentioning

confidence: 99%

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

2003

View full text Add to dashboard Cite

An investigation was carried out on the room temperature ageing of off-stoichiometric DGEBA/TETA epoxy formulations. The results obtained show that the epoxy rich mixtures have their inherent brittleness increased by the ageing treatment due to recrystalization of the unreacted epoxy monomers, although homopolymerization could also play a minor role. The initial reaction steps dominated by the amine addition reactions control the macromolecular structure and the mechanical performance of the stoichiometric and near stoichiometric formulation with excess of epoxy monomer. Plasticization due to absorbed -OH results on a significant increase of the deformability of these formulations. The amine rich mixtures have the more stable structures, although plasticization due to moisture absorption from the surrounding environment also produces an increase on the deformability of all, but one, of the formulations investigated. keywords: epoxy resins, ageing, mechanical propertiesoff-stoichiometric mixtures. For the particular system made of the triethylene tetramine, TETA, hardener and the DGEBA monomer the variation of the hardener to monomer ratio promotes strong changes on the mechanical behavior [18][19][20][21] . Of particular interest with respect to these changes is the very sharp increase in the impact strength, when amine rich mixtures were used 21 . The problem of working with off-stoichiometric mixtures is that latent reaction sites could remain on the macromolecular structure developed and under the proper conditions the structure can evolve, resulting in changes on the mechanical performance of the material. Temperature is clearly one external parameter that could cause changes to the system, but, even at room temperature, ageing due to exposure of the epoxy resin to humid environments could also be important [22][23][24] . The changes observed on the mechanical properties when the epoxy monomer to hardener ratio is varied, and the possible changes due to aging, are a direct consequence of the different macromolecular structures that are developed and/or the possible reactions that could occur given a

show abstract

Relationship between mechanical properties of and crack progogation in epoxy resin adhesives

Cited by 131 publications

References 24 publications

Crack Growth of Structural Adhesive Joints in Humid Environments

Crack Growth of Structural Adhesive Joints in Humid Environments

Experimental investigations of crack trapping in brittle heterogeneous solids

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

Contact Info

Product

Resources

About