Cracking Propagation of Hardening Concrete Based on the Extended Finite Element Method

Self-deformation cracking is the cracking caused by thermal deformation, autogenous volume deformation or shrinkage deformation. In this paper, an extended finite element calculation method was deduced for concrete crack propagation under a constant hydration and hardening condition during the construction period, and a corresponding programming code was developed. The experimental investigation shows that initial crack propagation caused by self-deformation loads can be analyzed by this program. This improved algorithm was a preliminary application of the XFEM to the problem of the concrete self-deformation cracking during the hydration and hardening period. However, room for improvement exists for this algorithm in terms of matching calculation programs with mass concrete temperature fields containing cooling pipes and the influence of creep or damage on crack propagation.

New insight into fracturing characterization of shale under cyclic soft stimulation:A lab-scale investigation

The cyclic soft stimulation(CSS)is a new method of reservoir reforming for which the mechanism of fracturing crack propagation is ambiguous with regard to the alternating fluid pressure.This study aims to provide a comprehensive understanding of the fracturing mechanical characterizations of CSS under different magnitudes and amplitudes of the alternating fluid pressure.Acoustic emission(AE)is recorded to investigate the damage evolution under CSS based on the b value analysis of AE.Experimental results reveal the difference of pressure in a crack under different cyclic fluid pressure conditions.The AE results show that the maximum radiated energy under CSS tends to be reduced with the increase in the amplitude and magnitude of the alternating fluid pressure.The finishing crucial touch is that the crack extending criterion under CSS is proposed,which combines the injection parameters,the rock properties and in-situ stress.According to the crack extending criterion,the fluctuation fluid pressure causes the reduction of a critical crack extending pressure,and the CSS causes the crack to initiate and propagate under low fluid pressure.Under a higher-value magnitude of alternating fluid pressure,the cyclic times of CSS is less for the crack initiation.In supplement to the crack extending criterion,a distinct relationship between the radiated energy and the cyclic fluid pressure also is established based on the energy dissipation criterion.These new findings provide an insight into the determination of crack extending criterion under CSS for efficiently implementing shale fracturing.

Effect of Cerium on Microstructures of Hard Alloys

Microstructures and crack extending characteristic of the YG8R,YT5R and YT14R hard alloys adding a trace cerium were studied by AEM and HVEM with a tensile holder.In the hard alloys adding cerium,the compounds of Ce_2O_3 or Ce_2O_2S could be formed,extending of stacking faults and transforma- tion from fcc Co to hcp Co were suppressed,volume fraction of fcc Co in the alloys was increased,and strength of Co and(TiW)C phases and grain boundaries were raised.Plastic deformation in Co phase near edges of the tensile cracks was more strong,and the tensile cracks could pass through some smaller WC grains.

An Extended Dielectric Crack Model for Fracture Analysis of a Thermopiezoelectric Strip

An extended dielectric crack model is proposed to capture the effects of the physical properties of crack interior on crack-tip thermoelectroelastic fields.The typical crack-face boundary conditions can be retrieved by considering the limiting cases of electrical permeability and thermal conductivity inside a crack.Making use of the Fourier transform technique,the problem of a thermopiezoelectric strip weakened by a Griffith crack is investigated and transformed to solve the system of the second kind Fredholm integral equations with Cauchy kernel.The Lobatto-Chebyshev collocation method is used to form a nonlinear system of algebraic equations,which is solved by elaborating on an algorithm.The crack-tip thermoelectroelastic fields are determined by using the approximate solutions.Numerical simulations are carried out to show the variations of the fracture parameters of concern under applied thermoelectromechanical loads,the physical properties of the dielectric medium inside the crack and the geometry of the cracked thermopiezoelectric strip.Some comparisons with the experimental results are reported to reveal the effectiveness of the extended dielectric crack model.