Elastic-plastic Deformation Research Articles

Incompatible Deformation Model of Rocks with Defects around a Thick-Walled Cylinder

Before the excavation of underground engineering, joints, fissures, and voids already exist in the rock—that is, there are defects in the rock. Due to the existence of these defects, the rock produces plastic deformation, which can lead to incompatible deformation. Therefore, the classic continuum theory cannot accurately describe the deformation of the rock. In this paper, a relationship between the strain tensor and metric tensor was studied by analyzing the three states of elastic plastic deformation, and the elasto-plastic incompatible model was built. Additionally, the stress and deformation of a thick-walled cylinder under hydrostatic pressure was investigated by using a finite element program written in the FORTRAN language. The results show that the plastic strain is associated with not only deviator stress but also the distribution of defects (represented by the incompatible parameter R). With the value of R increasing, the defects in the rock increased, but the elastic plastic stiffness matrix decreased. Thus, as more rock enters the plastic state, the deformation of the surrounding rock is enlarged.

Numerical evaluation of the residual stresses in shot peening of alloy steels

In the present numerical study, the residual stresses generated during the shot peening process were evaluated using the finite element method. The influence of shot velocity on the residual stress distribution due to the indentation of a rigid shot over the target plate of alloy steel was studied. The finite element package ABAQUS 6.20 is used for simulating the shot peening process considering the target plate to be deformable. A parametric study was performed by introducing strain hardening rate as H1 = 800 MPa, keeping the dimension of target plate same with variation in shot velocity 20, 50, 75, 100, 125, and 150 m s−1 to check the behavior of residual stress distribution. As the indentation takes place over the metallic target plate, elastic-plastic deformation was observed. The indentation of the shot with a different velocity range causes the difference in the depth and size of the dent and induces the compressive residual stress. For perfectly plastic and the strain hardened material, the residual stress contour was simulated. The simulated results for strain hardened material show the significant change in the compressive residual stress in the sub-surface region of the target plate. It is evident from the results that the shot velocity has a significant effect on the residual stress distribution. The maximum compressive residual stress is achieved when the shot is indented at a velocity of 125 m s−1.

Numerical study on the mechanism of air leakage in drainage boreholes: A fully coupled gas-air flow model considering elastic-plastic deformation of coal and its validation

Air leakage caused by mining-induced fractures around the borehole and roadway greatly affects the effect of underground gas drainage. Therefore, the study of the air leakage model considering three-dimensional stress and coal elastic-plastic deformation is of great significance to prevent air leakage. In this work, a model of air leakage outside borehole in mining-disturbed coal seam including a fully coupled gas-air flow and coal mechanics model and a mining-induced damage permeability model was developed and verified. The model was used to study the gas-air migration law and air leakage mechanism during gas drainage, and the influence of key parameters including initial permeability and sealing depth on gas drainage effect was analyzed. The results show: (1) The model can be used to characterize the air leakage of pre-drainage boreholes in mining-disturbed coal seams. (2) The gas and air pressure in the severe mining disturbance area rapidly decreased and increased in a short time. (3) Increasing the initial permeability and sealing depth will promote the gas flow in the borehole in the early stage, but the gas concentration will be reduced. The research results provide a scientific theoretical basis for improving the gas drainage effect and ensuring mining safety.

Temperature and strain monitor of COPV by buckypaper and MXene sensor combined flexible printed circuit

Pressure vessels are always under different hazards such as leaking, fracturing, and unknown deformation. In this work, the novel micro-nano sensors were introduced based on flexible printed circuit (FPC). The temperature cycling and hydraulic pressure cycling experiments were carried out. This kind of combined sensor can be embedded and arranged between inner tank and fiber layer without any defect. The experimental results show the new sensor can detect not only thermal strain, but also elastic deformation and plastic deformation caused by pressure. Also can reflect the yield limit of COPV, which can ensure the safety of manufacture.

Experimental Investigation on Strength and Failure Characteristics of Cemented Paste Backfill

The strength characteristics of cemented paste backfill (CPB) in mining areas are key control factors for the safety assessment of overlying strata. A series of experiments about uniaxial compression and triaxial compression were carried out to study the influence of cement content of filling slurry, curing age, and curing temperature on strength behavior of CPB specimens. The failure mechanism and damage feature of CPB have been investigated. The results show the following: (1) The uniaxial compressive strength of CPB specimens exhibits an upward trend with the increase of cement content and curing age. When the cement content is high, the uniaxial compressive strength increases sharply with increasing curing age. (2) The cohesion of CPB specimens increases with the increase of cement content of filling slurry, curing age, and curing temperature. The cohesion of CPB specimens with curing age 7 days and 14 days increases linearly with increasing cement content. At the later stage of curing age, the strength growth of high cement content backfill is significantly greater than that of low cement content. The internal friction angle of the filling increases slightly with increasing filling cement content, curing age, and curing temperature. (3) The shear strength of CPB specimens at curing age 7 days exhibits an upward trend with the increase of confining pressure, while the shear strength at 14 days and 28 days curing age decreases slightly as the confining pressure increases. (4) With the increase of cement content in backfill, the brittleness increases significantly when the backfill is damaged. The failure mode of CPB specimens changes from monoclinic section shear failure to X-type failure with increasing curing age, and the failure process is divided into four stages: pore compaction, linear elastic deformation, plastic deformation, and post-peak failure.

Fouling Simulations of a Passive Part of the Testing Combustion Facility

Results from the previous work of Strouhal et al. (2020) suggest that the used CFD fouling model together with user-implemented subroutines is not sufficient for obtaining satisfactory agreement with deposits observed in a described experimental device. The objective of this work is to create a basis for qualitative improvements of the simulation results. This includes using more detailed geometry and testing an influence of variation of parameters of two implemented fouling models. An accurate estimation of these parameters requires either empirical evidence from device operation or detailed information about fly ash composition and properties, which is usually accessible only for individual fly ash constituents. The goal of the sensitivity analysis was to show influence of these parameters on deposition rates, identify insignificant parameters for the tested range of particle properties and diameters and the most significant parameters for each of the six tested fly ash size fractions. To the authors’ knowledge, such an analysis is not present in available literature. The first tested model shown that one parameter to be significantly higher compared to other, except for the smallest particles. For the second model, all parameters were found to be significant at least for one examined particle diameter. Elastic deformation, plastic deformation and adhesion are thus considered important across the tested range of particle properties and sizes, at least for the fouling model used.

Predicting the mechanical behavior of a polypropylene-based nonwoven using 3D microstructural simulation

Based on filtration simulations, virtual filter media development is used to design new nonwoven microstructures with increased filtration performance. However, the processability in the subsequent manufacturing processes of these new designs is not guaranteed. The ability to predict the mechanical properties of the new designs is crucial to predict their processability. This paper introduces a microstructural simulation model based on micro-computed tomography scans (µCT scans) to predict the three-dimensional elastic-plastic behavior of nonwoven filter media with polypropylene fibers. A microstructural analysis is performed to investigate the requirements of a representative volume element (RVE). Digital twins of the µCT scans are modeled based on the microstructural analysis. The results of an RVE convergence study serve to corroborate the existence of RVEs for this kind of material. Microstructural simulations for the load cases of tension, compression, and shear in all three spatial directions are performed on µCT scans and digital twins. The calculations are validated using the results of an extensive 3D material testing program. The distinct deformation mechanisms under the load cases of tension, compression, and shear in the machine direction, cross direction, and z-direction are discussed. Finally, the results show the dependency of the effective elastic-plastic deformation behavior on a small number of selected microstructural parameters. This dependency enables the usage of digital twins to predict the deformation behavior of virtual microstructure designs.

A Simple Critical Response Evaluation Method for Base-Isolation Building-Connection Hybrid System Under Double Impulse as Representative of Near-Fault Ground Motion

We revisit a unique building system including a base-isolation, building-connection hybrid control system. The base-isolation system withstands pulse-type earthquake ground motions effectively and the building-connection system resists long-duration earthquake ground motions efficiently. A simple smart critical response evaluation method without nonlinear time-history response analysis is proposed for this hybrid building system under near-fault ground motions. An analytical expression of the maximum elastic-plastic deformation of a damped bilinear hysteretic single-degree-of-freedom (SDOF) model under critical double impulse as a representative of pulse-type ground motions derived in our previous paper plays an important role in the development of the simple critical response evaluation method. A two-step transformation procedure into an SDOF model is proposed. The first step is the transformation of the main base-isolated building into an SDOF system and the second step is the reduction of the connecting dampers supported on a sub building to a damper with a sophisticated compensation factor on an assumed rigid wall. The evaluation of damping coefficients with the consideration of yielding of the base-isolation story is a key step in this paper. Different from the previous work, the equivalent damping coefficient is derived depending on the response range before and after yielding of the base-isolation story. This treatment enhances the accuracy of the proposed method. The accuracy and reliability of the proposed response evaluation method is demonstrated by the time-history response analysis of the multi-degree-of-freedom (MDOF) model.

Numerical and Experimental Research on the Brushing Aluminium Alloy Mechanism Using an Abrasive Filament Brush.

Abrasive filament brushes have been widely used in surface processes for a wide range of applications, including blending, edge-radiusing, and polishing. However, the associated brush mechanics of material removal is still not clear. In order to analyze the brush grinding of aluminium alloy, this paper constructed a kinematic model of a single filament, simulated the scratch process of a single abrasive grain, and investigated the brush force and material removal based on the finite element approach. The simulated result shows that the brush grinding can be changed from elastic–plastic deformation to chip formation when increasing the brush speed to 1000 r/min. The normal and tangential forces increase linearly and quadratically with the increase in the rotation speed (500–5000 r/min), respectively, and increase linearly with the increase in the penetration depth (0.1–1 mm), which is consistent with the experiment results. In addition, the amount of material removal initially increases with the increase in penetration depth, and then decreases. This paper provides a new approach to understanding the process of material removal and is helpful for the selection of reasonable brush parameters in the intelligent grinding control application.

Changes in surface integrity of cemented tungsten carbide with shot peening treatment

This study investigates the changes in the surface integrity of WC-Co cemented carbide, after traditional and dual shot peening treatments, using physical characterization methods in conjunction with finite element simulations. Cast steel balls were used in traditional shot peening, while dual shot peening involved the additional use of ceramic shots. Tensile residual stress was found to coexist with compressive residual stresses within both the WC and Co phases, resulting in the fluctuation of stress amplitude in the surface layer. Steep stress gradients were mainly located in regions near the phase interface, especially around the WC/Co interface. In comparison with traditional shot peening, dual shot peening not only improved the uniformity of residual stress at both the macroscopic and microscopic levels but also refined the microstructure and returned the hardness dispersion to the original value by facilitating the simultaneous and coordinated evolution of the WC and Co phases during further deformation. However, the surface roughness increased significantly after traditional and dual shot peening treatments due to accumulated elastic-plastic deformation. This is likely to deteriorate the surface integrity and thus should be avoided if possible, without compromising the other beneficial effects caused by shot peening.

Reliability of results obtained by semi-analytical finite element method for prismatic bodies with variable physical and geometric parameters

To confirm the reliability of the results obtained on the basis of the semi-analytical finite element method using the approaches suggested in [1-2, 4-6], a wide range of test problems is considered. Within the framework of the elastic approach, the spatial problem of an unevenly loaded shell, the middle surface of which has the shape of an elliptical paraboloid, is considered. The validation of the reliability of solutions obtained on the basis of the semi-analytical finite element method for physically nonlinear problems is carried out using the example of elastic-plastic calculation of an unevenly heated cube, the physical and mechanical characteristics of the material of which depend on temperature. To substantiate the reliability of the results obtained when solving problems of large plastic deformations, the elastic-plastic deformation of a parallelepiped between plane-parallel plates in the absence of contact friction is considered.
 The efficiency of application of the semi-analytical finite element method to the calculation of curvilinear inhomogeneous prismatic objects is shown. The solution of the control problems of the theory of elasticity, thermoelasticity and thermoplasticity, as well as the problems of shape change, makes it possible to draw a conclusion about the reliability of the results of the study of the selected class of objects on the basis of the developed methodology and the applied software package that implements it.

Ultrasonic Pulsating Water Jet Peening: Influence of Pressure and Pattern Strategy.

Peening techniques are nowadays attracting more research attention due to their association with the extending of the service life and improving surface texture of engineering components. Ultrasonic pulsating water jet peening represents a new way of mechanical surface treatment. Accelerated water droplets via hammer effect cause small elastic-plastic deformations on the surface. This work deals with peening of aluminum alloy using an ultrasonic pulsating water jet, where periodically acting water droplets were used as the peening medium. The aim of the work was the feasibility study of the peening process and to observe the effects of pressure (p = 10, 20 and 30 MPa) and pattern trajectory (linear hatch and cross hatch). The peened surfaces were analyzed by the surface roughness profile parameters Ra and Rz and the microhardness along the peening axis into the material. Graphically processed results show a clear increase of measured values with increasing pressure (p = 10, 20 and 30 MPa), where the roughness values ranged from 1.89 µm to 4.11 µm, and the microhardness values ranged from 43.3 HV0.005 to 47 HV0.005, as compared to 40.3 HV0.005 obtained for the untreated sample. The achieved results indicate potential using of an ultrasonic pulsating water jet as a new method of surface treatment of metals. By controlled distribution of water droplets, it is possible to achieve a local distribution of surface roughness, and at the same time, strengthening of the subsurface layers in the material without thermal influence on the material.

Impact Resistance Analysis and Optimization of Variant Truss Beam Structure Based on Material Properties.

In order to meet the increasing application requirements with regards to structural impact resistance in industries such as mining, construction, aerospace engineering, and disaster relief and mitigation, this paper designs a variant truss beam structure with a large shrinkage ratio and high impact resistance. Based on the principle of the curved trajectory of scissor mechanisms, this paper conducts a finite element simulation analysis of the impact load on the truss beam structure, a theoretical analysis of the impact response and a relevant prototype bench-top experiment, completing a full study on the impact resistance mechanism of the designed variant truss beam structure under the impact load. In the paper, the buffer effect of the external load impact on the variant truss beam structure is analyzed from the perspective of the energy change of elastic–plastic deformation. This paper proposes an optimization strategy for the variant truss beam structure with the energy absorption rate as the optimization index through extensive analysis of the parameter response surfaces. The strategy integrates analyses on the response characteristic analysis of various configuration materials to obtain an optimal combination of component parameters that ensures that the strength of the truss beam structure meets set requirements. The strategy provides a feasible method with which to verify the effectiveness and impact resistance of a variant truss structure design.

The effect of Si and Ge on the elastic properties and plastic deformation modes in high- and medium-entropy alloys

We employ quantum mechanics modeling to investigate the effects of Ge and Si solute elements on the elastic properties and plastic deformation modes in two families of high-entropy alloys, CoCrFeMnNi and CoCrFeNi, and medium-entropy alloy, CoCrNi. The static lattice constants and single-crystal elastic parameters are calculated for these three face-centered-cubic random solid solutions as a function of composition. Using the elastic constants, we analyzed mechanical stability, derived polycrystalline modulus, and evaluated solid-solution strengthening for these multi-component alloys. We fabricated (CoCrFeNi)100−x Six (x = 0, 4, 6) and measured the polycrystalline modulus and hardness. The calculated trends for Young's and shear modulus as well as lattice parameters were verified by our measurements. The dependence of generalized stacking fault energy on Ge and Si was studied in detail for the considered multi-component alloys. The competition between various plastic deformation modes was revealed based on effective energy barriers. Our calculations predict that the activated deformation modes in all the alloys studied here are the stacking fault mode (dominant) and the full-slip mode (secondary), and as the concentrations of Ge and Si increase, twining becomes favored.

Algorithm of finite elemental SSS analysis of thin-walled technosphere objects based on a triangular discretion element with elastic-plastic deformation

The article describes an algorithm for the strength calculation of thin-walled objects of the technosphere, taking into account the plastic stage of the work of the material used, which is quite relevant with the increased requirements for material saving of designed and reconstructed objects. The finite element method is used as a tool for studying the stress-strain state of technosphere objects, taking into account the physical nonlinearity of the applied structural material. As a sampling element, a fragment of the middle surface of a thin-walled triangular technosphere object with main nodes at the vertices of the triangular element and additional nodes at the midpoints of the sides is used. The sought unknowns at the main nodes at the loading step are the increments of the displacement vector components and their first derivatives with respect to the curvilinear coordinates of the middle surface. At additional nodes, Lagrange multipliers act as unknowns, introduced to improve the consistency of the bin along the boundaries with adjacent elements. When deriving the plasticity matrix at the loading step, we used the hypothesis that the components of the stress increment tensor are proportional to the components of the strain increment tensor. The developed algorithm was implemented as a package of applied programs and verified by the example of calculating a rigidly restrained cylinder loaded with internal pressure.

Estimation of the Elasticity Modulus of Composite Electroplated Coatings during Their Layer-by-Layer Deposition

Introduction. To keep automobiles and tractors in operation conditions, it is necessary to restore the inner cylindrical surfaces of the friction pair parts. This is the most laborintensive activity. The method of electroplated contact deposition of composite coatings, based on elastic plastic deformation of formed layers, is used for repairing surfaces. To use this method it is necessary to determine the values of the elasticity modulus, on which the wear resistance of tribocouplings depends. Materials and Methods. For the study, cylindrical samples made of 30 HGSA and 30 HGSNA steels were used. Electrolyte containing 200–250 g/l chromium oxide, 2.0–2.5 g/l sulfuric acid, and distilled water was used for electroplating the coatings. When calculating the stress-strain state, the apparatus of continuum mechanics was used. Results. The dependence of the coating pliability as a function of the parameters of individual elementary layers is determined. When the multilayer coating of three types (orthogonal-reinforced, cross-reinforced and quasi-isotropic) is applied, its structure does not depend on the angles of kinematic tool movement on the inner cylindrical surface of the part. For each type of coatings, the way to determine the constant stiffness coefficients of the layers is specified. The dependences for calculating the elasticity modulus of the applied material are derived from the values of the stiffness coefficients. Discussion and Conclusion. In determining the modulus of elasticity of multilayered composite coatings, the calculation is made for the individual layers by passing to the convective coordinates, which is in complete agreement with the Lagrange point of view on the study of the motion of a continuous medium. The results obtained are of practical significance in the selection of the coating material to be applied for the restoration of internal cylindrical surfaces.

Laboratory Study of Deformational Characteristics and Acoustic Emission Properties of Coal with Different Strengths under Uniaxial Compression

Acoustic emission (AE) can reflect the dynamic changes in a material’s structure, and it has been widely used in studies regarding coal mechanics, such as those focusing on the influence of loading rate or water content change on the mechanical properties of coal. However, the deformational behavior of coals with various strengths differs due to the variation in microstructure. Hard coal presents brittleness, which is closely related to certain kinds of geological disasters such as coal bursts; soft coal exhibits soft rock properties and large deformation mechanical characteristics. Therefore, conclusions drawn from AE characteristics of a single coal sample have application limitations. This paper studies the deformation patterns and AE characteristics of coals with different strengths. A uniaxial compression experiment was carried out using coal samples with average uniaxial compressive strengths of 30 MPa and 10 MPa; the SAEU2S digital AE system was used to measure the AE counts, dissipation energy, and fracturing point distributions at each deformation stage of the different coals. The results show that the bearing capacity of hard coal is similar to that of the elastic stage and plastic deformation stage, but it may lose its bearing capacity immediately after failure. Soft coal has a relatively distinct stress-softening deformation stage and retains a certain bearing capacity after the peak. The AE counts and dissipation energy of hard coal are significantly higher than those of soft media, with average increases of 49% and 26%, respectively. Via comparative analysis of the distribution and development of internal rupture points within soft coal and hard coal at 15%, 70%, and 80% peak loads, it was observed that hard coal has fewer rupture points in the elastic deformation stage, allowing it to maintain good integrity; however, its rupture points increase rapidly under high stress. Soft coal produces more plastic deformation under low loading conditions, but the development of the fracture is relatively slow in the stress-softening stage. We extracted and summarized the AE characteristics discussed in the literature using one single coal sample, and the results support the conclusions presented in this paper. This study subdivided the deformation process and AE characteristics of soft and hard coals, providing a theoretical guidance and technical support for the application of AE technology in coal with different strengths.

Research on optimization of micro-milling process for curved thin wall structure

In order to satisfy the increasing fabrication quality requirements of micro curved thin wall structures, deformation, burrs height and dimensional errors in micro-milling processes of curved thin walls are studied. At first, the finite element analysis of curved thin wall deformation is carried out, it shows that complex elastic-plastic deformation and recutting occur in each micro-milling layer. Appropriate radial depth of cut, smaller spindle speed and axial depth of cut are beneficial to reduce deformation. Then, the influence of key process parameters in micro-milling as the speed of spindle n, feed engagement fz, radial depth of cut ae and axial depth of cut ap on milling force (Fn), burrs height (H) and dimensional errors (△w) are analyzed using the response surface method (RSM). To facilitate the quantitative analyses, mathematical models of burrs height and dimensional errors are established considering the interactions and quadratic effects of key parameters. It shows that the interactions among key parameters cannot be ignored. Therefore, cutting parameters should be delicately selected. The multi-objective particle swarm optimization (MOPSO) experiments are carried out based on the established prediction model. The results show that the combination of the optimized parameters identified by this method can effectively reduce the burr height and the dimensional error. Finally, under the guidance of this method, high-quality curved thin wall parts are fabricated.

Microstructure-based deformation and fracture modeling of particulate reinforced composites with ordinary state-based peridynamic theory

The aim of this study is to develop a microstructure-based peridynamic (PD) model to predict the elastic–plastic deformation and fracture mechanism of the particulate reinforced composites. The developed state-based PD model is validated against the previous experimental study on the aluminum matrix reinforced by Sic particles. Three representative volume elements (RVEs) are extracted from a scanning electron microscope image by image processing, and the particle morphology is investigated. Methods are proposed to assign boundary conditions and allocate material properties to matrix/particle interface regions and calculate the surface correction in the PD computational framework for the particulate composites. Two different loading paths are simulated (loading and loading–unloading-reloading). Distribution of residual stress and residual plastic strain are obtained after unloading. Before damage initiation, the stresses in the particles, especially at the sharp corners, are relatively higher than in the matrix. The particle, matrix, and interface damage are detected in the analysis. Damage initiation occurs in narrow particles and matrices sandwiched by particles. The initiated microcracks are propagated and coalesce to make the principal crack, and the final fracture occurs by the propagation of the principal crack. It is found that the proposed model can accurately predict the main deformation and damage behavior of particulate composites.

Nano-Indentation Hardness and Strain Hardening of Silicon, Sodium Chloride and Tungsten Crystals

BackgroundA previous review of micro- and nano-indentation hardness tests and their analyses gave emphasis to obtaining measurements of continuous nano-indentation load, P, versus, depth, h, recordings that monitor the full elastic–plastic deformation behavior of a localized crystal volume [1].ObjectiveAttention is given to determining the complete, indentation-based, elastic–plastic deformation properties of the local volume, including the initial crystal elastic deformation behavior and, especially to evaluation of post pop-in plastic strain hardening.MethodStress–strain calculations are presented for an initial Hertzian elastic loading and follow-on crystal micro- and nano-scale plastic deformation responses [2].ResultsApplied load, P, dependencies on contact diameters, di, of silicon crystals are compiled on the basis of elastic, plastic and cracking predictions, giving indication at the lowest P values of an indentation size effect (ISE) for the crystal hardness. Elastic–plastic stress–strain curves are presented for sodium chloride and tungsten crystals. The hardness and strain hardening calculations also demonstrate an influence of the ISE.ConclusionsThe exceptional plastic strain hardening behaviors scale dimensionally with corresponding dislocation interactions and sessile reactions within the very localized plastic indentation zones. There is usefulness in determining elastic modulus values from the initial loading record. Micro- and nano-scale dislocation interactions/reactions account for the high stress and strain hardening levels as well as the occurrence of an ISE.