Papers by Keyword: Dynamic Stress Intensity Factor

Abstract: The researchers and scientists have concluded that material dynamic fracture properties must be considered during the design stage of the modern structure. The dynamic stress intensity factor is very important in understanding of material dynamic behavior. Keeping in view the importance of the materials dynamic stress intensity factor: an efficient and reliable numerical-analytical procedure is developed for calculation of dynamic stress intensity factor. For this, three-dimensional model of a Modified Hopkinson Pressure Bar (MHPB) and a specimen is modeled and analyzed with the ANSYS software. Transient dynamic analysis technique is used for simulation of load-variations as a function of time. As an output of analysis, values of load point displacement and Crack Mouth Opening Displacement (CMOD) are obtained. These values are substituted into two different analytical formulas for calculation of a dynamic stress intensity factor. The results obtained are compared with previous published results, and a good agreement is found.

Abstract: A theoretical analysis is followed to calculate the dynamic stress intensity factors (DSIFs) in transversely isotropic piezoelectric bi-materials, due to existence of a permeable interfacial crack, near the edge of a circular cavity. The model is subjected to dynamic incident anti-plane shearing (SH-wave) and the formulation based on Green's function method. Conjunction and crack-simulation techniques are applied to obtain DSIFs at the crack’s outer tip. Calculations are prepared based on FORTRAN language program. A comparison is accomplished between the present model and another model with a crack emerging from the cavity edge to calibrate the program. Calculating results showed the influences of the physical parameters, the structural geometry and the wave frequencies on the dimensionless DSIFs and how those affected the efficiency of piezoelectric devices and materials.

Abstract: In transversely isotropic piezoelectric bi-materials, a theoretical analysis is followed to calculate the dynamic stress intensity factors (DSIFs) due to existence of a permeable interfacial crack, near the edge of a circular cavity. The model is subjected to dynamic incident anti-plane shearing (SH-wave) and Green's function method is the base of formulation. Conjunction and crack-simulation techniques are applied to obtain DSIFs at the crack’s inner tip. Calculations are prepared based on FORTRAN language program. For calibration of program, a comparison is accomplished between the present model and another with a crack emerging from the cavity edge. Calculating results clarified the influences of the physical parameters, the structural geometry and the wave frequencies on the dimensionless DSIFs and how those affected the efficiency of piezoelectric devices and materials.

Abstract: Using the Laplace transform and freezing time variable, the problem in the time domain into the frequency domain to solve the problem. The establishment of a crack unit model in the frequency domain, and the boundary integral equation and discrete form containing the crack unit has been deduced. While using Durbin algorithm suitable for transient dynamic response of the inverse Laplace transform, the amount of stress intensity factor of a set of transformation parameters corresponding to the frequency domain into a time domain to obtain the dynamic stress intensity factor of time curve, and calculate the stress intensity factor compared to the boundary finite element method has a Laplace transform high precision, easy to save CPU time and data preparation features, we recommend using this method to calculate the dynamic stress intensity factor.

Abstract: Recently, some improvements made to machine performance have caused accidents as a result of impact fracture. These fractures were caused by unexpected dynamic loads. To suppress the damage in these accidents, it is necessary to clarify the dynamic fracture mechanism, many reports have been published on dynamic fracture phenomena [1, 2, 3]. Cast iron is used to repair some structural and mechanical parts following fracture accidents. The brittle behavior of cast iron is not desirable for preventing dynamic fracture. It is necessary to clarify the dynamic fracture mechanism of cast iron for the safety design and maintenance of structures. The dynamic behavior of deformation and fracture depends on the size of a structure. In some cases, an experimental approach using specimens at industrial scale is difficult. As a first step, dynamic fracture without a huge mass effect should be discussed. In this study, a normal sized three point bending specimen consisting of cast iron was used in dynamic experiment. An ultra-high speed camera was used to observe crack propagation. Some fractures were caused under eccentric loading, non-straight cracks propagated in this condition. According to the experimental results, the path and velocity of crack propagation were estimated. Fracture criteria were discussed from the results of numerical simulation. To simulate the behavior of crack propagation a moving finite element method based on Delaunay automatic triangulation was used. The prediction of fracture paths based on the fracture mechanics theory was demonstrated in these numerical simulations. The predicted fracture path agreed with the experimental fracture path.