Totally found 412 items.

  • [期刊] Numerical investigation on the effect of well interference on hydraulic fracture propagation in shale formation
    Due to the low permeability of shale reservoir, the multiple well fracturing technologies are widely used for the development of shale gas. In this paper, a numerical model coupled rock deformation, fracturing fluid flow to investigate the effect of well interference on fracture dynamic propagation in multiple well fracturing. The simulation results indicate that asymmetric fracture propagations occur in multi-well fracturing, and the lateral growths of interior fractures are suppressed due to the intense inter-well stress interference. With the increase well space, the effect of inter-well stress interference decreases gradually. The case studies also indicate that, for successful fracturing treatment, a possible lower limit of well spacing should be considered in design, to avoid a sharp reduction of effectiveness in treatment. Meanwhile, the optimized well space obtained from zipper fracturing is tighter than that from conventional well factory hydraulic fracturing. Compared with the conventional well factory hydraulic fracturing, the zipper fracturing has a better performance in improving the stimulated reservoir volume and decrease the effect of inter-well stress interference, which is favorable to enhance hydrocarbon production.
  • [期刊] The interface behavior of a thin film bonded imperfectly to a finite thickness gradient substrate
    The interface behavior of a thin film bonded imperfectly to a finite thickness gradient substrate with or without an adhesive interlayer is investigated in the present paper. The governing integro-differential equations for such an interface problem are formulated based on the equilibrium and compatibility conditions. The distribution of the interfacial shear stress and the transverse stress in the thin film is comprehensively studied. The stress singularity near the bonded edges is also focused on. It is found that a more durable film and a more reliable interface could be achieved if Young's modulus of the substrate decreases in its thickness direction. The effect of the adhesive interlayer is to change the stress field, which acts like a "rubber gasket in mechanical engineering" to reduce the stress concentration at the interface. The result should be very useful for the design of various film/substrate systems in flexible and stretchable electronic devices.
  • [期刊] Use of the stress gradient factor to estimate fatigue stress concentration factors K-f
    Stress concentration effects in unavoidable notches reduce fatigue strengths and lives of most structural components, so they must be properly quantified when designing and analyzing them. The Stress Gradient Method (SGM), based on classic Fracture Mechanics concepts and on short crack ideas, can be used to calculate Stress Gradient Factors (SGF) and to properly estimate fatigue stress concentration factors K-f. The procedures proposed here to calculate them are general and only require the normal stress distribution ahead of the notch tip and material properties. The SGF concept is defined to differentiate it from the geometric stress concentration factor K-t, also present in stress intensity factor equations for cracks. Using short crack, SGM concepts, and SGF, a general equation is proposed to compute K-f, which is discretized to be used with any numerical methods (a short C + + algorithm is presented to solve it). Experimental K-f data are used to validate the proposed method, showing good agreement with its predictions, especially for sharp notches.
  • [期刊] Simulations of fracture tests of uncharged and hydrogen-charged additively manufactured 304 stainless steel specimens using cohesive zone modeling
    Fracture tests of uncharged and hydrogen-charged single edge bend specimens of additively manufactured 304 stainless steels are simulated using the cohesive zone modeling (CZM) approach. Two-dimensional plane strain finite element analyses without cohesive elements are conducted to identify the values of cohesive energy. Similar analyses using CZM with the trapezoidal traction-separation laws are then conducted. The best-fit cohesive parameters show the values of cohesive strength for the uncharged specimens are higher than those for the hydrogen-charged ones whereas the value of cohesive energy for the uncharged specimens can be either slightly lower or higher than that for the hydrogen-charged ones.
  • [期刊] Review on failure behaviors of fusion welded high-strength Al alloys due to fine equiaxed zone
    Fine eQuiaxed Zone (FQZ) close to the fusion line is a common and unique microstructural feature for fusion welded high-strength Al alloys particularly when containing Zr element. It is well believed that the presence of FQZ can degrade the fatigue cracking resistance and tensile strength of the joints. Thus, a thorough knowledge on the formation and microstructure due to FQZ and resultant softening and failure mechanisms is necessary to be well understood on the damage tolerance and structural integrity of fusion welded joints. Current paper reviews the relevant aspects mentioned above as an important reference to be capable of correlating the microstructural response with service performance. Some potential solutions to coordinate the FQZ are therefore discussed. Furthermore, few papers up to date have focused on the fatigue and fracture mechanisms related with FQZ inside high-strength Al alloy fusion welds. By combining conventional characterization and numerical modelling approach, the high-resolution synchrotron radiation X-ray computed microtomography shows great potential in revealing the competition mechanism between FQZ and welding defects on the cracking behavior.
  • [期刊] A study of induced delamination and failure in woven composite laminates subject to short-beam shear testing
    Failure in woven composite laminates subject to global shear load is studied. Laminates are manufactured, tested and analyzed using X-ray computed tomography, scanning electron microscopy and finite element models. It is found that the stress distribution along the thickness direction is dependent on the layer shifting that alters different yarn interactions, which in turn, affects delamination and failure onset A suggested failure mechanism is in agreement with experimental observations.
  • [期刊] 3D analysis of anchor bolt pullout in concrete materials using the non-ordinary state-based peridynamics
    In this work, a meshless analysis based the non-ordinary stated-based peridynamic method (NSPD) is performed to solve the problem of anchor bolt pullout in plain concrete. The peridynamic method is adopted as an analysis tool to avoid the difficulties found in FEM. In the analysis, the Drucker-Prager plasticity model is implemented to describe the nonlinear relationship between force vector state and deformation vector state. The Hughes and Winger algorithm is integrated in NSPD for large deformation analysis. The whole progressive failure process of the 3D anchor system, consisted of five groups with different embedment depth or member thickness, are investigated. Numerical analysis results indicate that the obtained peak pullout load shows good agreement with the current design formula and the crack branching of anchoring system also agreed well with the experimental investigations.
  • [期刊] A comparative study by using two different log-periodic power laws on acoustic emission signals from LiF specimens under compression
    The deformation of solid materials up to the point of fracture is followed by acoustic emission (AE) signals. The cumulative acoustic energy released during such a process seems to generally follow a power law form, which is compatible with the view that the fracturing process is a phenomenon with developing critical dynamics. In the present work, the cumulative energy released by the AE signals emitted during the deformation of LiF samples has been calculated and fitted by two different fitting functions, which are both power laws decorated with log-periodic corrections. The comparison of the produced results would lead to the conclusion of whether each one of the two equations can produce valid acoustic energy release modeling, which can describe the fracturing procedure of solid materials and its underlying mechanics. It should be noted that one of the models managed to fit the experimental data more accurately in the majority of the cases studied. We show that both of the studied log-periodic models managed to acceptably fit the data, which means that this field of study could possible lead to new methods of predicting the time point of a material's failure. In conclusion, this comparative study reveals that these models could be a valuable tool in cases of monitoring materials or structures being under load at the region of their mechanical tolerance.
  • [期刊] A homogenized multigrid XFEM to predict the crack growth behavior of ductile material in the presence of microstructural defects
    In this work, stable crack growth behavior of SA508 carbon steel has been evaluated through experimental and numerical investigations. The effect of various types of flaws has been observed on the load carrying capacity of the structures. A homogenized multigrid XFEM approach has been proposed to simulate the stable crack growth in ductile material using finite strain plasticity. The geometric nonlinearity has been modeled by updated Lagrangian approach whereas the material nonlinearity has been modeled by von-Mises yield criterion using isotropic strain hardening. The accuracy and effectiveness of the proposed approach has been verified by solving several stable crack growth problems. (C) 2016 Elsevier Ltd. All rights reserved.
  • [期刊] A note on the defect sensitivity of brittle solid foams
    The fracture behavior of brittle solid foams of different densities and regularities is numerically analyzed in finite element models. The findings provide insight into the complex fracture phenomenon in cellular materials and reveal a size influence from a dominant microstructure on the global fracture mechanism. It is observed that a crack of length of about three times the average cell size in the foam is needed to obtain localization of nucleated fractures to the vicinity of the initial defect At cracks smaller than this critical size, the fractures nucleate at randomly positioned high-stressed regions in the foam far away from the initial crack, i.e. the structure is seemingly insensitive to the initial defect Further, it is found that irregular (i.e. randomly positioned cells) foams are more insensitive to defects than perfectly ordered foams if all other parameters are similar and thus indicate that classical fracture theories for solid foams have to be slightly modified.
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