A review of T-stress and its effects in fracture mechanics

Mixed mode fracture behavior of PMMA, was studied experimentally and theoretically using four different test configurations and with different crack types. Although all the test samples were subjected to three-point bend loading but completely different mixed mode fracture behaviors were observed for the tested samples. For each test configuration, especial mixed mode fracture toughness curves were obtained for fracture initiation direction and fracture toughness in the whole ranges of mixed mode I/II loading conditions. The level of crack tip constraint in the tested samples (which is related to the stress intensity factors ( K ) and the T -stress) was used as the main affecting parameter for predicting the mixed mode fracture results based on a two parameter ( K-T ) fracture theory. It was observed that the loss of crack tip constraint in the tested samples increases the mixed mode fracture resistance and decreases the fracture initiation direction and vice versa.

Mixed mode fracture toughness testing of PMMA with different three-point bend type specimens

In this research, the plane stress fracture toughness of ultra-fine grained aluminum specimens produced through accumulative roll bonding (ARB) process was investigated for the first time. The specimens were produced successfully by the ARB process up to 7 cycles with the amount of 50% thickness reduction in each cycle at room temperature without using lubricant. The fracture toughness was evaluated for the annealed and different ARB cycles using ASTM E561 standard and compact tension specimens. Additionally, mechanical properties, tensile fracture surfaces and crystallite size of ultra-fine grained aluminum ARBed specimens were evaluated by uniaxial tensile tests, microhardness measurements, scanning electron microscopy and X-ray diffraction. By increasing the number of the ARB cycles, fracture toughness was increased and the maximum value of this parameter was achieved in the last cycle, which was approximately 25.4 MPam1/2 that it increased by 155% higher than the annealed specimen. Results of X-ray diffraction demonstrated that by increasing the number of the ARB cycles, crystallite size decreased so that it reached 175 nm for the 7th cycle ARBed specimen from 1341 nm for annealed samples. Furthermore, by increasing the number of the ARB cycles up to the 7th cycle, tensile strength and microhardness of ultra-fine grained aluminum increased to 232 MPa and 51VHN, respectively. At first, the value of elongation decreased and then increased. The SEM results showed that ductile fracture mode with large dimples occurring in the annealed specimen, changed to shear ductile fracture with elongated sophomoric shear and fine dimples after the ARB process.

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Experimental evaluation of the plane stress fracture toughness for ultra-fine grained aluminum specimens prepared by accumulative roll bonding process

Fracture loads prediction of the modified 3D-printed ABS specimens under mixed-mode I/II loading

In this article, fracture behavior of multi-layered composite processed via accumulative roll bonding (ARB) method has been investigated. At first, Al1050/Cu/MgAZ31B multi-layered composite has been prepared by ARB through seven passes. The microstructure and mechanical properties have been evaluated using uniaxial tensile test, microhardness test and optical microscope, respectively. Then, the plane stress fracture toughness of Al1050/Cu/MgAZ31B have been studied via R-curves. Also, tensile fracture surfaces have been demonstrated by scanning electron microscope (SEM). The results of microstructure investigations have indicated that plastic instability occurred for both pure Cu and Mg AZ31B reinforcing at the primary sandwich and uniform distribution has been processed. By increasing the applied strain, the values of microhardness for the three layers Al1050, pure Cu, and Mg AZ31B as well as ultimate tensile strength (UTS) have been significantly increased, continually, and UTS has reached to the maximum value of 355.5 MPa. SEM images of the tensile rupture surfaces in the different ARB passes have demonstrated that with increasing the applied strain, the fracture mode converted to shear ductile at the last ARB pass. Results of fracture test have shown that by increasing the applied strain, the value of fracture toughness have been raised, continually and at the third pass reached to the maximum value of 40.4 MPam1/2. Also, the trends of fracture toughness for Al1050/Cu/MgAZ31B were in great matching with the conclusions of the fracture behavior investigation of Al1050 produced by ARB.

Fracture toughness investigation of Al1050/Cu/MgAZ31ZB multi-layered composite produced by accumulative roll bonding process

Effect of equal channel angular pressing on fracture toughness of Al-7075

Determination of crack tip parameters for ASCB specimen under mixed mode loading using finite element method

In this paper, finite element method is implemented to model stranded-wire helical springs under different loading conditions. Finite element results are coupled with multiaxial fatigue criteria su...

Hossein Darban

Papers

Effect of equal channel angular pressing on fracture toughness of Al-7075

Determination of crack tip parameters for ASCB specimen under mixed mode loading using finite element method

Multiaxial fatigue analysis of stranded-wire helical springs: