Strength, stability and size effects in the brittle behaviour of bonded joints under torsion: theory and experimental assessment

Abstract

This paper describes a simple Griffith fracture energy criterion to predict the brittle failure load for tubular or non‐tubular bonded joints subjected to torsion. The theoretical solution generalizes to non‐tubular bonded joints an analogous result already presented in the literature and experimentally validated for particular tubular bonded joints. The stability of brittle crack propagation and the size effects on mechanical collapse behaviour, as well as the ductile–brittle transition, are analysed. Experimental measurements of failure loads under torsion for non‐tubular bonded joints agree satisfactorily with the theoretical predictions.

A generalization of the Coulomb’s friction law: from graphene to macroscale

“…Following [18][19][20][21][22], we find the identical result reported in Eq. (4b), if we assume an equivalent dissipated energy per unit surface 2γ given by:…”

“…We treat the scheme reported in Fig. 1(a) according to elasticity and energy balance, following previous approaches [18][19][20][21][22][23]; in this paper we introduce friction (i) and we demonstrate that the sliding can be treated as a "delamination" but taking place at a reduced "equivalent surface energy" that is correlated to friction and adhesion (ii). Accordingly, following [18][19][20][21][22][23], the solution posed by elasticity for the maximum shear stress arising at the interface of the two layers (the stress peak will take place at the end of the element with the higher rigidity, thus is symmetric for our considered identical layers), having Young's modulus E 1,2 (E 1,2 = E for identical layers), crosssectional areas A 1,2 (A 1,2 = A = bh for identical layers) and contact length l = 2c, in the presence of friction becomes: …”

“…Is friction dominated by the friction shear strength, by the friction force or by the dissipated energy? Coupling elasticity and energy balance [18][19][20][21][22][23][24][25][26][27] with molecular dynamics (MD) [27][28][29][30] and statistical simulations [31][32][33][34] we solve in this paper such controversy.…”

Strength prediction of tubular composite adhesive joints under torsion

“…If the shear strain in the adhesive is dominant and other strain components are small enough to be neglected, the maximum shear strain criterion, rather than the maximum strain criterion, can be used to predict the adhesive bulk failure. The fracture energy criterion can provide a reasonable prediction of brittle failure load for adhesive joints with isotropic adherends when the bonding length is sufficiently long [19,20]. However, it gives somewhat less accurate predictions for composite adhesive joints and does not consider the variation of failure torques with bonding length [15].…”

Thermal loading in multi-layered and/or functionally graded materials: Residual stress field, delamination, fatigue and related size effects

“…The related size and shape effects are also discussed. The statically indeterminate stress analysis is solved coupling equilibrium, compatibility and constitutive equations, and extending the approach already established for torsional loading on bi-component prismatic or cylindrical (Pugno, 1999(Pugno, , 2001Surace, 2000, 2001;Pugno and Carpinteri, 2002) beams in static or dynamic regime. Regarding fracture, the attention is posed on delamination between the layers due to brittle or fatigue thermally induced crack propagations.…”