Test protocols

Linear elastic fracture mechanics test protocols



The protocol is based upon a linear-elastic fracture-mechanics (LEFM) approach and is designed to be used to determine the value of the adhesive fracture energy, GIC, (more generally termed the adhesive fracture toughness) of structural adhesives under Mode I loading. It has been developed under the auspices of the "European Structural Integrity Society (Polymers, Adhesives and Composites TC4 Committee)".

The spreadsheets are included to enable the calculations to be performed from using:

1. Tapered double-cantilever beam (TDCB) specimens.

2. Double-cantilever beam (DCB(LB)) specimens, loaded via using loading blocks.

3. Double-cantilever beam (DCB(DH)) specimens, loaded via using drilled holes.


B.R.K. Blackman and A.J. Kinloch, "Fracture Tests for Structural Adhesive Joints", in "Fracture Mechanics Testing Methods for Polymers, Adhesives and Composites", Eds. A.Pavan, D.R.Moore and J.G.Williams, (Elsevier Science, Amsterdam), to be published, 2001.

Peel test protocols



Flexible laminates are used in a wide range of industrial and packaging applications. In general, there will be considerable practical importance associated with the adhesive strength between two specific adjacent layers in these laminates. Historically, peel strength (peel force per unit width) has been used as a measure of adhesive strength. However, it has been recognised [1] that this does not resolve the important contribution from plastic bending energy (GP) during the peel process. Therefore, most current approaches to the determination of adhesive strength involve the measurement of adhesive fracture toughness (GA) (also known as adhesive fracture energy or interfacial work of fracture, and sometimes also termed Gc), where:

GA= G - Gp

G is the total input energy for peeling.

The wide application of peel tests means that several test geometry forms have been used. Three particular forms are fixed arm peel and T-peel, but roller assisted peel in the form of mandrel peel tests is also used. Two protocols are available for these tests; one for fixed arm and T-peel and another for mandrel peel.

Fixed Arm and T Peel

In the fixed arm and T-peel protocol, the input energy (G) is measured and the plastic bending energy (GP) is calculated from knowledge of the tensile stress-strain behaviour of the peel arm material. In order to conduct calculations of GP, three approaches can be used and these will be described later. In order to accommodate all methods for describing the stress-strain behaviour of the peel arm and also to accommodate non-negligible values of the adhesive bond-line thickness, further analysis has been written [2]. Moreover, in order to properly describe the nature of plasticity of the peel arm other analytical considerations have been made [3]. These relate to the constraint on the peel arm and in the latest analysis it has been shown experimentally [4] and by modelling [3] that a fully unconstrained peel arm is the appropriate description.

The three methods of calculating GP are:

(i) Bilinear: a bilinear fit to the stress-strain curve and an analytical calculation of GP [2,3].

(ii) Linear-power law: a linear elastic - power law plastic fit to the stress-strain curve and an analytical calculation of GP [2,3].

(iii) Digitised: digitisation of the stress-strain curve and a numerical calculation of GP [5].

These approaches are required because the calculation of GP is not tractable without some analytical or numerical description of the stress-strain behaviour of the peel arm material. In principle, the numerical approach is best but not always workable. In any case, in order to make the method practical, it is necessary to first complete the other two methods and then to use the parameters for the numerical calculations which otherwise would take too long on current-day equipment.

Software packages are helpful in order to conduct the calculations of GP and also the subsequent calculations of GA. ICPeel (2006) is used to accommodate both bilinear and linear-power law approaches. The tensile stress-strain curve is fitted to either a bilinear function or a linear elastic power law plastic function. This fitting provides parameters for elastic modulus (E), work hardening coefficients (a and n, respectively) and yield co-ordinates (sy and/or ey) (see the protocol for full details). ICPeel (2006) should be used first, since the numerical method will require the curve fitting parameters. The numerical analysis is conducted with the software package ICPeel (Digitised) 2007 [5].

Mandrel Peel

The mandrel peel method does not require these analytical considerations because both GA and GP can be determined directly by experiment. Full details are in the test protocol.


1. A.J. Kinloch, C. C. Lau, and J. G. Williams Int. J. Fracture, 66, (1994), pages 45-70.

2. I. Georgiou, H. Hadavinia, A. Ivankovic, A.J. Kinloch, V. Tropsa, J.G. Williams, The Journal of Adhesion, 79, 1-27 (2003).

3. J.G. Williams, H Hadavina, B Cotterell, Int Journal of Solids and Structures,42 (2005), 4927-4946.

4. L.F. Kawashita, D. R. Moore, J. G. Williams J. Mat. Sci. 40, (2005) 1-8.

5. L.F. Kawashita The Peeling of Adhesive Joints PhD thesis University of London 2006.