Fracture assessment of notched short glass fibre reinforced polyamide 6: An approach from failure assessment diagrams and the theory of critical distances

Prediction of fracture loads in PMMA U‐notched specimens using the equivalent material concept and the theory of critical distances combined criterion

“…Understanding notches as any kind of macroscopic stress risers in the material, these may be responsible for structural failures caused by static fracture-plastic collapse processes, or the initiators of fatigue processes which may cause a crack to initiate, propagate, and eventually lead to failure. 7,[37][38][39][40][41] The TCD is based on linear-elastic assumptions, although it has been successfully applied to elastic-plastic situations, either through the direct consideration of elastic-plastic stress fields, 2 or through the assumption of linear-elastic behaviour (stress field) and the corresponding calibration of the inherent strength (see Section 2). In such cases, if the defects are blunt, it is generally over-conservative to proceed on the assumption that the defects behave like sharp cracks, Nomenclature: a, defect size; B, specimen thickness; E, elastic modulus; K , strain-hardening coefficient; K c , fracture resistance measured in stress intensity factor units; K I , stress intensity factor; K Ic , fracture toughness; L, critical distance; n, strain-hardening exponent; P LM est , estimation of critical load by using the line method; P PM est , estimation of critical load by using the point method; P max , maximum (critical) load; W, specimen width; ε f * , strain at crack initiation for the virtual brittle material; ε P , true plastic strain; ε u , engineering plastic strain at maximum load; ε u,True , true plastic strain at maximum load; ε Y , elastic strain at yield point; ε Y P , true plastic strain at yield point; ρ, notch radius; σ, true stress; σ av , average stress along a given distance; σ f * , tensile stress at crack initiation for the virtual brittle material; σ u , ultimate tensile strength; σ Y , yield strength; σ 0 , inherent strength; EMC, equivalent material concept; FE, finite elements; LM, line method; LSY, large-scale yielding; MSY, moderate-scale yielding; PM, point method; PMMA, polymethyl-methacrylate; SED, strain energy density; SENB, single edge notched bending (specimen); SSY, smallscale yielding; TCD, theory of critical distances given that notched components develop a load-bearing capacity that is greater than that developed by cracked components.…”

“…[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] The TCD methodologies have been successfully applied to different failure mechanisms (eg, fracture, fatigue) and materials, and are particularly simple to implement in structural integrity assessments. 7,[37][38][39][40][41] The TCD is based on linear-elastic assumptions, although it has been successfully applied to elastic-plastic situations, either through the direct consideration of elastic-plastic stress fields, 2 or through the assumption of linear-elastic behaviour (stress field) and the corresponding calibration of the inherent strength (see Section 2). 4,5 In any case, when the material behaviour is not completely linear-elastic, the application of the TCD requires the fracture testing of notched specimens, finite elements modelling, or both, in order to calibrate the material parameters involved (the critical distance, L, and the inherent strength, σ 0 ).…”

Coupling Finite Element Analysis and the Theory of Critical Distances to Estimate Critical Loads in Al6060-T66 Tubular Beams Containing Notches

“…In this sense, when dealing with notch assessments, there are two main types of criteria: the global criterion (based on the use of a notch stress intensity factor, analogously to ordinary fracture mechanics), and local criteria (based on the study of stress or strain fields around the notch tip). Among the latter, the theory of critical distances (TCD) stands out, and its applicability in fracture assessments has been widely reported in the literature for a variety of materials (such as polymers [12,13], metals [14,15], composites [16], or ceramics [17,18]). Moreover, the TCD has also been validated to analyze phenomena such as fatigue [19] or environmentally assisted cracking [20] and has been applied to different length scales [19,21,22].…”

On the use of British standard 7910 option 1 failure assessment diagram to non‐metallic materials

“…There have been some previous works providing FAD assessments of non‐metallic materials containing crack‐like defects. Some of them use the FADs provided by structural integrity procedures, whereas others apply theoretical FADs such as those derived from the strip yield model or the modified inherent flaw model which, in practice, are not commonly used by industry. This work, beyond providing additional validation on a number of non‐metals, provides theoretical justification of the use of BS7910 option 1 FAD (also gathered in SINTAP and FITNET FFS procedure) on non‐metallic materials.…”

“…There have been some previous works providing FAD assessments of non-metallic materials containing crack-like defects. Some of them [5][6][7][8] use the FADs Nomenclature: a, crack length; A p , plastic area under the load-displacement curve in a fracture test; b 0 , initial remaining ligament; B, specimen thickness; e max , strain under maximum load; E, elastic modulus; f(L r ), function of L r defining FAD; J, J integral; J e , elastic component of J; K mat , material fracture resistance measured by stress intensity factor; K I , stress intensity factor; K IC , fracture toughness; K r , fracture ratio of applied K I to fracture resistance; L r , ratio of applied load to limit load; P, applied load; P L , limit load; N, strain hardening exponent; η, dimensionless constant; W, specimen width; σ u , ultimate tensile strength; σ 0.2 , 0.2% proof strength; FAD, failure assessment diagram; FAL, failure assessment line; PMMA, polymethylmethacrylathe; SGFR-PA6, short glass fibre-reinforced polyamide 6 provided by structural integrity procedures, 2,3 whereas others 9 apply theoretical FADs such as those derived from the strip yield model [10][11][12] or the modified inherent flaw model 11 which, in practice, are not commonly used by industry. This work, beyond providing additional validation on a number of non-metals, provides theoretical justification of the use of BS7910 option 1 FAD (also gathered in SINTAP and FITNET FFS procedure) on non-metallic materials.…”