I think you might be mistaken in calling this experiment simple. The immediate problem I envisage is generating a suitable internal interfacial crack at the required interface, that is assuming you can engineer the interface to be perpendicular to the principle tensile stress. The nearest thing we do/have done to this is to notch then grow a fatigue crack along an interface, then do a K1C type fracture mechanics test. By a combination of fracture surface examination (SEM) and metallography on a plane perpendicular to the crackes we can determine if the fast crack followed the interfacial path. IIRC we have gone this on welds looking at weld/haz, and haz/parent.

Theoretically the relationships for edge cracks and internal cracks are all available in the fracture mechnics literature.

The only other way is put your faith in luck, i.e. you pull the internally cracked sample apart and trust that the initation defect has a recognisable appearance which is different to the propagated fast crack. But try that in a lot of materials and you will be doing a tensile test rather than a fracture mechanics test. I can imagine that in the composites field they have looked at the effect of interfacial/bonding defects on fracture stress/behaviour, i.e. materials where deformation is mostly elastic, which we would can instrinsically brittle.

International Journal of Fracture

1999, Volume 99, Issue 3, pp 143-161 A methodology for measuring interface fracture properties of composite materials

Leslie Bank-Sills, Nahum Travitzky, Dana Ashkenazi, Rami Eliasi

I think you might be mistaken in calling this experiment simple. The immediate problem I envisage is generating a suitable internal interfacial crack at the required interface, that is assuming you can engineer the interface to be perpendicular to the principle tensile stress. The nearest thing we do/have done to this (metallurgical field) is to notch then grow a fatigue crack along an interface, then do a K1C type fracture mechanics test. By a combination of fracture surface examination (SEM) and metallography on a plane perpendicular to the crackes we can determine if the fast crack followed the interfacial path. IIRC we have gone this on welds looking at weld/haz, and haz/parent to see how the crack propagates and the effect on the overall fracture resistance.

Theoretically the relationships for edge cracks and internal cracks are all available in the fracture mechnics literature. IIRC the edge crack and internal crack aren't that different as long as you call the length of the edge crack 'a', and that of the internal crack 2a. For an internal disc shaped crack LEFM gives something like K1 = {(2 x stress)/Pi} x SQRT(Pi x a).

The only other way is put your faith in luck, i.e. you pull the internally cracked sample apart and trust that the initation defect has a recognisable appearance which is different to the propagated fast crack. But try that in a lot of materials and you will be doing a tensile test rather than a fracture mechanics test.

However I can imagine that in the composites field they must have looked at the effect of interfacial/bonding defects on fracture stress/behaviour, i.e. and these are materials where deformation is mostly elastic, which we would call instrinsically brittle in the metallurgical field. Here's what I pulled up with just a quick search. Indeed it apears they have techniques and results for such work, not surprising really.

I would contact one of the leading lights in the field directly with this query.

International Journal of Fracture

1999, Volume 99, Issue 3, pp 143-161 A methodology for measuring interface fracture properties of composite materials

Leslie Bank-Sills, Nahum Travitzky, Dana Ashkenazi, Rami Eliasi

If you do a search you can find quite a few relevant papers Banchi et al., Zubelewicz, Buyukozturk, etc. etc.

Banks-Sills, L. (2014), 50th Anniversary Article: Review on Interface Fracture and Delamination of Composites. Strain, 50: 98–110. doi: 10.1111/str.12082

ABSTRACT

In this review paper, a methodology for measuring the interface fracture toughness of a crack between two isotropic, homogeneous materials and a delamination between two laminae of unidirectional composite materials of differing directions is presented. Four cases are considered. Two isotropic material pairs are described: glass/epoxy and two ceramic clays. Similar studies are presented for two cross-ply laminates: 0°/90° and +45°/−45. The Brazilian disk specimen was used to carry out mixed mode fracture tests. The load and crack or delamination length at fracture were measured and used in a finite element analysis to determine the displacement field. An interaction energy or M-integral was used to obtain the stress intensity factors at failure. These in turn were employed to calculate the critical interface energy release rate and two phase angles ψ and φ, which measure the mode mixity. For the M-integral and for each interface crack or delamination, the first term of the asymptotic solution of the fields is required. For two isotropic materials, these solutions are well known. For the laminates described here, they were determined by the Stroh and Lekhnittski formalisms. A failure criterion determined from first principles is presented. The values of , ψ and φ are used to specify the criterion for each material pair. A statistical analysis is presented, which predicts a 5% probability of failure.

Thanks for your answer. I am not trying to do experiments. I need experimental measurements to check a simple interface crack model.

I understand, good luck, all modellers need such work.

It sounds like you stole my project. I am working on same thing but I don't have results yet. Lets see what people have in store.

This measurement is important to check the following interface crack problem presented in a recent paper intitled "Interface crack loaded in tension: introducing an internal shear stress promoted by the Poisson's effect"; see our contributions in ResearchGate

Fracture mechanics of interfacial cracks is an area of current research interest. You will find a large number of recent articles in the literature. Prof. Leslie Bank-Sills and her colleagues have published quite a few in-depth studies, both experimental and numerical- on this technologically important issue.

Thanks, we shall look much more carefully the contributions quoted above in order to see if informations can be obtained regarding the questions opened by my recent modelling

Available experimental results are plots of critical crack extension force (interfacial toughness) as a function of phase angle that is a measure of shear/tension ratio. The interfacial toughness increases deeply with phase angle.

In our modelling, the shear/tension ratio increases with crack length; also, the reduced crack extension force increases deeply with crack length. In this way, a confrontation of our modelling with available experimental works is in the right direction (work in progress)

We have focussed, carefully, on two available experiments:

1) Banks-Sills and Ashkenazi (2000) using bi-material Brazilian disk specimens: in these tests, in mode I loading, the loading frame disturbs (inhibits) significantly Poisson's contractions. This experiment is not adapted to check the effect of the internal shear stress promoted by Poisson's effect.

2) Liechti and Chai (1992) using edge-cracked bi-material strip specimens: here, the tip of the initial starter crack is close to the middle of the specimen. In this region, the internal shear stress due to Poisson's effect is small. Poisson's effect contributes obviously to the observed asymmetry in interfacial fracture toughness versus phase angle.

Edge-cracked bi-material strip specimen may deserve consideration in estimating the exact magnitude of the contribution of Poisson's effect to the fracture toughness in experiments similar to Liechti and Chai, JAM, 1992. The geometry of the specimen, vis a vis the internal shear stress due to Poisson, is different from the one we have adopted in our modelling.

We are expecting that the asymmetry in fracture toughness versus phase angle, observed by Liechti and Chai (JAM, 1992) may be explained by an induced internal shear stress across the interface promoted by Poisson's effect (work in progress).

The asymmetry is due to the fact that in one direction, the applied shear stress acts in the same direction than the internal shear stress: this increases much more the crack extension force; and in the opposite direction, the overall shear stress is reduced; this leaves unchanged the fracture toughness with respect to the phase angle, over a much more larger range of phase angle values.

We have opened the following Q&A: What is the origin of the asymmetry in interfacial fracture toughness versus phase angle observed by Liechti and Chai (J.A.M., 1992) in epoxy/glass?

Please refer to our contribution "Interface crack under mixed mode I+II loading and internal shear stress due to Poisson's effect: theoretical analysis and confrontation with experiments" for a confrontation with Liechti and Chai (JAM,1992) experiments: reasonable agreement between theory and experiments is achieved