Numerical Investigation Of Fracture Research Articles

Numerical investigation of fracture in double-edge notched FGM plates under tension load

Purpose The purpose of this paper is to introduce a numerical investigation used to calculate the J-integral of the main crack behavior emanating from a semicircular notch and double semicircular notch and its interaction with another crack which may occur in various positions in (TiB/Ti) functionally graded material (FGM) plate subjected to tensile mechanical load. Design/methodology/approach For this purpose the variations of the material properties are applied at the integration points and at the nodes by implementing a subroutine USDFLD in the ABAQUS software. The variation of the J-integral according to the position, the length and the angle of rotation of cracks is demonstrated. The variation of the J-integral according to the position, the length and the angle of rotation of cracks is examined; also the effect of different parameters for double notch FGM plate is investigated as well as the effect of band of FGM within the ceramic plate to reduce J-integral. Findings According to the numerical analysis, all parameters above played an important role in determining the J-integral. Originality/value The present study consists in investigating the simulation used to calculate the J-integral of the main crack behavior emanating from a semicircular notch and double semicircular notch and its interaction with another crack which may occur in various positions in (TiB/Ti) FGM plate under Mode I. The J-integral is determined for various load applied. The cracked plate is joined by bonding an FGM layer to TiB plate on its double side. The determination of the gain on J-integral by using FGM layer is highlighted. The calculation of J-integral of FGM’s involves the direction of the radius of the notch in order to reduce the J-integral.

Mode I fracture in PMMA specimens with notches – Experimental and numerical studies

This paper shows the results of experimental and numerical investigation of fracture in PMMA (Polymethyl-methacrylate) plate specimens under mode I. Samples had two thicknesses (9.7 and 18 mm) and they were weakened by two types of edge-notches: rounded V-notch with radius 0.5 mm and U-notch with radius 10 mm. During tests, critical load value, fracture initiation point and fracture initiation angle were obtained. Additionally, the fracture process was recorded by a high-speed PHANTOM camera. Crack length growth and changes in crack tip velocity over time were analyzed. Stress and strain fields under the critical load value were calculated using Finite Element Method (FEM). Three-dimensional isoparametric elements were used and non-linearity of material and geometry was also included. A stress–strain criterion for notched specimens under tension was proposed.

Experimental and numerical investigation of fracture in fillet welds by cross joint specimens

The load capacity of fillet welds is investigated experimentally and numerically in cross joint specimens with the objective of calibrating multiple failure criteria for the ductile fracture of weld metal. The cross joint specimens are composed of mild shipbuilding steel with plate thicknesses of 20 mm and 30 mm respectively. The fillet welds are manually produced by flux-cored arc welding, using the filler metal Elgacore MXX100. To achieve different stress states in the weld joints, forces in two different directions and moments about two different axes are applied separately on various specimens. A uniquely designed specimen is employed for each load scenario. For the numerical investigations, an appropriate discretization of the weld joints is established by taking into account the distribution of the metallographic structure with the weld metal and the heat-affected zone. The distribution of the different materials is determined by a macrosection of a weld joint. The material behavior, in terms of true stress-strain curves for the weld metal and the material of the heat-affected zone, is identified by hardness measurements. With the established discretization of the weld joints and true stress-strain curves of the different materials, the experimentally determined force-displacement curves are reproduced in finite element analyses. Furthermore, the Gurson (1977) damage model are successfully calibrated for the weld metal.

Experimental and numerical investigation of fracture in a cast aluminium alloy

This paper describes an experimental and numerical investigation on the fracture behaviour of a cast AlSi9MgMn aluminium alloy. In the experiments, a modified Arcan test set-up was used to study mixed-mode fracture. During testing, the tension load and the displacement of the actuator of the test machine were recorded, simultaneously as a high-resolution digital camera was used to record a speckle-patterned surface of the specimen. The recorded images were post-processed using an in-house digital image correlation (DIC) software to obtain information of the displacement and strain fields in the specimen during the test. In addition, some newly implemented features in the DIC software allowed us to detect and follow the crack propagation in the material. The numerical calculations were carried out with a user-defined material model implemented in an explicit finite element code. In the model, the material behaviour is described by the classical J 2 flow theory, while fracture was modelled by the Cockcroft–Latham criterion, assuming the fracture parameter to follow a modified weakest-link Weibull distribution. With the proposed probabilistic fracture modelling approach, the fracture parameter can be introduced as a random variable in the finite element simulations. Crack propagation was modelled by element erosion, and a non-local damage formulation was used to reduce mesh-size sensitivity. To reveal the effect of mesh density and meshing technique on the force–displacement curves and the crack propagation, several different meshes were used in the numerical simulations of the modified Arcan tests. The numerical results were finally compared to the experimental data and the agreement between the measured and predicted response was evaluated.

A numerical study of intergranular fracture and oxygen embrittlement in an elastic-viscoplastic solid

We present results from a numerical investigation of fracture along an embrittled surface embedded in an elastic-viscoplastic solid, an idealized model for high-temperature intergranular fracture in nickel-base superalloys. The formulation includes coupled models for the mechanical response, stress-assisted diffusion of oxygen, and a moving cohesive interface that determines crack initiation, growth and arrest. The entire system is formulated in a frame that translates with the crack tip and is implemented in an adaptive, space-time finite element code that supports both transient and direct steady-state calculations. We present a criterion for stable crack growth specific to the moving cohesive interface model and apply it to studies of fracture along a planar grain boundary with uniform cohesive properties. No stable solutions were found for the steady case. In the transient case, the stability criterion resolves a lack of uniqueness in the incremental solutions for growing cracks. Results are reported for monotonic loading to failure, linear ramp to sustained hold at a peak load level and cyclic loading. We investigate the sensitivity of the response to the loading rate, the cohesive interface properties and the degree of overload past crack initiation. Finally, we extend the cohesive interface model and the stability criterion with a phenomenological model for oxygen embrittlement and report the effects of embrittlement on steady-state response.

Experimental and numerical investigation of fracture in double-edge notched steel plates

Double-edge notched (DENT) steel plates were pulled until complete fracture and several experimental observations were made (using profilometry and scanning electron microscopy). The essential work of fracture (EWF) model was found to be well verified. Numerical simulations - up to the maximum load only - of some experiments were performed using the finite element method (FEM), and incorporating geometric and material non-linearities (large deformation elasto-plasticity). Some experimental measurements were compared with the corresponding numerical computations and excellent agreement was found.