Crack blunting mechanisms in polymers

Kinloch, A. J.; Williams, J. G.

doi:10.1007/bf00552112

Cited by 252 publications

(112 citation statements)

References 20 publications

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“…In the unaged samples, it can be observed the presence of a large crack initiation region that indicates, according to theoretical thermoset polymer crack propagation, that a significant energy value was necessary for crack initiation 23 . This ductile behavior is also shown in the stress-strain curve which presented elongation at failure close to 8%, related to the absence of post cure treatment in the polymeric system.…”

Section: Fractographymentioning

confidence: 78%

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The effects of water absorption on an ester vinyl resin system

Sobrinho¹,

Ferreira²,

Bastian³

2009

Mat. Res.

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Derakene is a vinyl ester resin largely employed as matrix for polymeric based composite systems. In this work, the performance of such polymeric system was evaluated considering the effect of hygrothermal aging. The mechanical and thermal properties were examined for the processed material before and after ageing in water at 60 °C for a maximum period of 64 days. Both analyses indicated the occurrence of post cure of the system after 16 days due to exposition at 60 °C in water, which was also confirmed by analyses in samples with post cure treatment. Moreover, it was observed plasticizing of resin after 36 and 64 days of ageing. Micro structural and fracture surface analyses were carried out in order to characterize the samples. The appearance of surface voids was also observed.

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Section: Fractographymentioning

confidence: 78%

“…Of particular relevance for this study is the size of the mirror region, which has been correlated with the toughness of polymers and particulate composites 23,24 . The smaller the mirror region, the more brittle the material is.…”

Section: Fractographymentioning

confidence: 99%

The effects of water absorption on an ester vinyl resin system

Sobrinho¹,

Ferreira²,

Bastian³

2009

Mat. Res.

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“…From previous work [20,21], it is suggested that the reason for the unstable crack growth is that the wedge impacting the specimen initially gives rise to a relatively blunt crack, or notch, when it first makes contact with the adhesive bead formed in the 'V' of the specimen. However, in the case of the more brittle adhesives, the blunt crack rapidly sharpens to form a 'naturallysharp' running crack.…”

Section: Unstable Crack Growthmentioning

confidence: 99%

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Blackman

Kinloch

Taylor

et al. 2000

Journal of Materials Science

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The impact wedge-peel (IWP) test is an International Standard (ISO 11343) method that is employed to measure the resistance to cleavage fracture of structural adhesives at a relatively high test-rate of 2 to 3 m/s. In the present work this test has been employed to evaluate the performance of a range of structural adhesives when used to bond either steel or aluminium-alloy substrates. Firstly, a novel test arrangement for performing these tests, using a high-speed servohydraulic machine, is described. Tests were performed at 10 -4 and 2m/s and at test temperatures of -40°C and 23°C. High-speed photography was also used to investigate the failure of the IWP test specimens. Both stable and unstable types of crack growth were recorded, with the crack propagating cohesively through the adhesive layer in all cases. The methods of data analysis recommended by the International Standard are critically reviewed, and some shortcomings are highlighted. Secondly, the results from the IWP test are then directly correlated to the measured values of the adhesive fracture energies, G c , of the adhesives, which were determined using a fracture-mechanics approach. Finally, it is demonstrated that, from knowledge of the value of G c of the adhesive, coupled with a finite-element analysis of the IWP test geometry, the failure behaviour of the IWP specimen may be successfully modelled and predicted.

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“…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

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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

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Crack blunting mechanisms in polymers

Cited by 252 publications

References 20 publications

The effects of water absorption on an ester vinyl resin system

The effects of water absorption on an ester vinyl resin system

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

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