جستجوی مقالات مرتبط با کلیدواژه "mode i fracture toughness" در نشریات گروه "فنی و مهندسی"

This work presents the hollow center cracked disc (HCCD) test and the cracked straight through Brazilian disc (CSTBD) test of oil well cement sheath using the experimental test and Particle Flow Code in two-dimensions (PFC2D) in order to determine mode I fracture toughness of cement sheath. The tensile strength of cement sheath is 1.2 MPa. The cement sheath model is calibrated by outputs of the experimental test. Secondly, the numerical HCCD model and CSTBD model with diameter of 100 mm are prepared. The notch lengths are 10 mm, 20 mm, 30 mm, and 40 mm. The tests are performed by the loading rate of 0.018 mm/s. When the notch length in CSTBD is 40 mm, the external work is decreased 48%, related to the maximum external work of model with notch length of 10 mm (0.225 KN*mm decreased to 0.116 KN*mm). When the notch length in HCCD is 30 mm, the external work is decreased 33%, related to the maximum external work of model with notch length of 10 mm (0.06 KN*mm decreased to 0.04 KN*mm). The fracture energy is largely related to the joint length. The fracture energy is decreased by increasing the notch length. In constant to the notch length, the fracture energy of the CSTBD model is more than the HCCD model. Mode I fracture toughness is constant by increasing the notch length. The HCCD test and the CSTBD test yield a similar fracture toughness due to a similar tensile stress distribution on failure surface. The experimental outputs are in accordance to the numerical results.

This work presents the Semi-Circular Bend (SCB) test and Notched Brazilian Disc (NBD) test of shotcrete using experimental test and Particle Flow Code in two-dimensions (PFC2D) in order to determine a relation between mode I fracture toughness and the tensile strength of shotcrete. Firstly, the micro-parameters of flat joint model are calibrated using the results of shotcrete experimental test (uniaxial compressive strength and splitting tensile test). Secondly, numerical models with edge notch (SCB model) and internal notch (NBD model) with diameter of 150 mm are prepared. Notch lengths are 20 mm, 30 mm, and 40 mm.  The tests are performed by the loading rate of 0.016 mm/s. Tensile strength of shotcrete is 3.25 MPa. The results obtained show that by using the flat joint model, it is possible to determine the crack growth path and crack initiation stress similar to the experimental one. Mode I fracture toughness is constant by increasing the notch length. Mode I fracture toughness and tensile strength of shotcrete can be related to each other by the equation, σt = 6.78 KIC. The SCB test yields the lowest fracture toughness due to pure tensile stress distribution on failure surface.

As fracture toughness (KIC) is one of the most practical parameters in fracture mechanics of rock, this article aims to investigate this parameter both experimentally and numerically. In the current research, mode-I fracture toughness of a kind of limestone was investigated by performing Brazilian disc, cylinder direct tension and under bending cubs. Through performing some tests on straight notched Brazilian disc specimen (SNBD), the effect of specimen diameter and crack length on the rock mode-I fracture toughness was investigated. Moreover, in order to determine the effect of the loading type on the mode I fracture toughness; two other tests were conducted on the cylinder direct tension specimens and cubic specimens (DT and SENB). Then, the effect of the crack length and the specimen diameter on the rocks mode-I fracture toughness was investigated through conducting the statistical analysis of variance (ANOVA) on the results obtained in DT and SNBD tests. In order to determine the requiredparameters of DT and SNBD specimens for fracture toughness, finite-element software was used. The results showed that by increasing the diameter from 75 mm to 95 mm, for Brazilian disc specimens the average fracture toughness increases by 30%. Also it seems that factors such as the test and loading type as well as the crack geometry can affect the fracture roughness parameter.