The Quantification of Micro-structural Damage of Weak Muddy Intercalation in Dry-wet Cycles Combining in-situ SEM and DIP

In order to reflect truly the damage evolution mechanism of weak muddy intercalation in dry-wet cycles, two typical weak muddy intercalations were selected for dry-wet cycles. The mineral changes of specimens were analyzed via X-ray diffraction after dry-wet cycles. By combining in-situ SEM and digital image processing(DIP), the damage evolution process and damage characteristic parameters of each stage were obtained. The experimental results indicate that the hydration and dissolution of minerals can not be a determinant factor in structure damage. The micro-structural damage is due to disintegration of mineral aggregates, leading to changes in the number and size of cracks and pores. The damage degree of specimens is related to its initial structure, and the micro-structural damage intensifies and finally tends to stabilize with cycle times increased.

Multi-scale elastoplastic mechanical model and microstructure damage analysis of solid expandable tubular

We present an in-depth study of the failure phenomenon of solid expandable tubular (SET) due to large expansion ratio in open holes of deep and ultra-deep wells. By examining the post-expansion SET, lots of microcracks are found on the inner surface of SET. Their morphology and parameters such as length and depth are investigated by use of metallographic microscope and scanning electron microscope (SEM). In addition, the Voronoi cell technique is adopted to characterize the multi-phase material microstructure of the SET. By using the anisotropic elastoplastic material constitutive model and macro/microscopic multi-dimensional cross-scale coupled boundary conditions, a sophisticated and multi-scale finite element model (FEM) of the SET is built successfully to simulate the material microstructure damage for different expansion ratios. The microcrack initiation and growth is simulated, and the structural integrity of the SET is discussed. It is concluded that this multi-scale finite element modeling method could effectively predict the elastoplastic deformation and the microscopic damage initiation and evolution of the SET. It is of great significance as a theoretical analysis tool to optimize the selection of appropriate tubular materials and it could be also used to substantially reduce costly failures of expandable tubulars in the field. This numerical analysis is not only beneficial for understanding the damage process of tubular materials but also effectively guides the engineering application of the SET technology.

Quantitative characterization of deformation and damage process by digital volume correlation:A review

Characterizing material 3D deformation and damage is a key challenge in mechanical research. Digital volume correlation （DVC）, as a tool for quantifying the internal mechanical response, can comprehensively study the extraction of key failure parameters. This review summarizes the recent progresses in the study of the internal movement of granular materials, inhomogeneous deformation of composite materials, and stress intensity factor around a crack front in static and fatigue states using DVC. To elaborate on the technique＇s potential, we discussed the accuracy and efficiency of the algorithm and the acquisition of real microstructure data within the material under a complex environment.

Effects of Strain Rate and Fiber Content on the Dynamic Mechanical Properties of Sisal Fiber Cement-Based Composites

In this paper,a split Hopkinson pressure bar(SHPB)was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites(SFRCCs),and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy(SEM)and energy-dispersive X-ray spectrome-try(EDS).The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials.Compared with ordinary cement-based composites(OCCs),the SFRCCs demonstrate higher post-peak strength,ductility,and energy absorption capacity with higher fiber content.Moreover,the SFRCCs are strain rate sensitive materials,and their peak stress,ultimate strain,and energy integrals all increase with increasing strain rate.From the perspective of fracture failure characteristics,the failure of OCCs is dominated by the brittle failure of crystal cleavage.In contrast,the failure mode of the SFRCCs changes to microscale matrix cracks,multi-scale pull-out interface debonding of fibers(fine filaments and bundles),and mechanical interlock.This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.

BEHAVIOUR OF INITIATION AND GROWTH OF SHORT FATIGUE CRACKS

Rotary bending fatigue tests were carried out using smooth specimens of a medium-carbon steel with two different grain sizes.The process of early crack development was observed by the replica method,and the effects of grain size and microstructure on short crack development were studied.It was shown that the initiation process of fatigue cracks is that the damaged region is intensified gradually,and the growth of short cracks relates to the coalescence of cracks.The grain size and microstructure have a great influence upon the initiation and growth of short cracks.A reasonable definition was given in relation to short fatigue crack initiation and propagation.

A review of surface damage/microstructures and their effects on hydrogen/helium retention in tungsten

The change in surface damage/microstructures and its effects on the hydrogen(H)isotope/helium(He)dynamic behavior are the key factors for investigating issues of tungsten(W)-based plasma-facing materials(PFMs)in fusion such as surface erosion,H/He retention and tritium(T)inventory.Complex surface damage/microstructures are introduced in W by high-temperature plasma irradiation and new material design,typically including pre-damage and multi-ion co-deposition induced structures,solute elements and related composites,native defects like dislocations and interfaces,and nanostructures.Systematic experimental and theoretical researches were performed on H isotope/He retention in complex W-based materials in the past decades.In this review,we aim to provide an overview of typical surface damage/microstructures and their effects on H/He retention in W,both in the experiment and multiscale modeling.The distribution/state,dynamics evolution,and interaction with defects/microstructures of H/He are generally summarized at different scales.Finally,the current difficulties,challenges and future directions are also discussed about H/He retention in complex W-based PFMs.