Papers by Keyword: Process Zone

Abstract: A mode I, centre crack, in ductile steel plate of finite dimensions is modeled in ANSYS software. Non-linear stress-strain data of steel are used. Plane strain case is adopted. A suitable value of far field tensile stress (pressure) is chosen such that EPFM condition prevails at the crack tip. Process and plastic zones are obtained at the crack tip. Desired values are noted. Areas of high stress and high strain are identified. Validation of void nucleation taking place ahead of crack tip and not exactly at the crack tip and coalescence of voids happening at the crack tip are confirmed from the results. Plots between the distance of desired location from the crack tip and load line stresses and strains are drawn. The plots are in accordance with the expectations.

Abstract: The paper presents the stress field, obtained with the help of finite element method, around Mode I crack tip in ductile steel under EPFM regime. Process, plastic and non-K compliant elastic zones develop. Void nucleation ahead of the crack tip is observed in the process zone. The stress solution in the plastic zone is validated with theoretical HRR solution. In the elastic zone, as expected, substantial error is observed between K dominated LEFM solution and numerical EPFM values.Nomenclature

Abstract: The paper presents a numerical technique to estimate the critical value of J integral, of a ductile metal (Aluminum alloy). Cracked, Single Edge Notch Bend (SENB) specimen of the alloy is modeled by finite element method. Load over the specimen is chosen such that the process or fracture zone is generated at the crack tip. The load is subsequently increased for the process zone size to go up. Process zone sizes and displacements under loads are measured from post processor solutions. Resistance curve and blunting line are plotted. Intersection of the two provides the value of. equals upon fulfillment of the plane strain condition. Various thickness values of the specimen are tried. The value of K_IC obtained from is found to be in close agreement with the reported value obtained from experiments.Nomenclature

Abstract: Based on initial discontinuity state (IDS) of material, this paper presents a preliminary analytical model which was developed to evaluate the effect of exfoliation corrosion on the residual fatigue life of upper wing skins. A life prediction was then carried out using constant amplitude compression dominated loading for various exfoliation corrosion levels by AFGROW, and the prediction agreed reasonably with the available test data. The result suggest that exfoliation can be treated as a process zone located initially at a surface, and then at the base of an evolving general stress concentration representing the loss of material in the exfoliation region. The major effect of the exfoliation corrosion on fatigue life is to cause a dramatic reduction in life with small corrosion depths, and most of the fatigue effect is associated with the introduction of small pits, rather than more general stress concentration associated with the bulk of the exfoliation attack. But the effect of pit on fatigue life is gradually reduced with increasing pit size. A pit with a constant depth can be applied to the model described in this paper for long exposure structure. A preliminary recommendation for the pit depth is about 0.3mm for LY12CZ.

Abstract: The formation of fracture process zones in polygranular reactor core moderator graphites subjected to four-point bending has been investigated. The three-dimensional digital image correlation technique has been combined with resistance strain gauge measurements to evaluate, both the localised and the global displacements during testing. The non-linear load-displacement characteristics prior to peak load are correlated with the localised displacements which can extend up to ~3mm (process zone) from the tensile surface of the specimen. At peak load a macro-crack propagates rapidly along an irregular path controlled by the direction of the applied tensile load and the microstructure of the graphite. These cracks arrest prior to complete separation of the specimen. Localised tensile process zones extend for distances of up to ~3mm ahead of the tips of these cracks.

Abstract: When studying the growth of triaxial-stress-state crack, the plastic work rate consumed in the process zone at crack tip should be described clearly. Fracture for a cracked specimen is related to rupture of a simple uniaxial tensile specimen by nature. By equaling the crack tip stress-strain field to uniaxial stress-strain field, it is obtained that the plastic work rate consumed in the process zone at crack tip can be expressed by the plastic energy density WF multiplied by the equivalent size of the process zone hF. The plastic energy density WF can be expressed by virtue of uniaxial true stress-strain curve. And analytical form of hF for triaxial stress state is presented by recourse to three-dimensional analyses on material behaviors. The expression of plastic work rate consumed in the process zone is verified by the predicting fracture toughness.

Abstract: For explaining the SCG behavior of polyethylene, the crack layer theory is applied based on the description of two driving forces: crack and PZ. The relations between the speed of SCG, crack length and elapsed time are the most important characteristics of polyethylene resistance to crack propagation, or long-term brittle fracture. The crack layer model of slow crack growth in polyethylene is designed in such a way that it qualitatively reproduces the main features of the process indicated above and makes it possible to quantitatively match any pattern of step-wise crack growth. In this paper, the behavior of SCG of polyethylene is developed for numerical simulation based on the crack layer theory. Some parametric study and applications are addressed based on the developed simulation program.