Indentation Zone Research Articles

Impact of pleating on the filtration performance of fibrous air filters

Pleated fibrous air filters are widely used for aerosol filtration but the impact of pleating on its filtration performance is still lacking detailed analysis. Pleating results in changes in thickness of the filter media (indentation or bulge zone) and it is generally difficult to simulate the particle filtration process of a pleat due to large difference in scale between that of the pleat and fiber. To address this problem, a dual-scale simulation method is developed in this study by combining the fiber-scale and pleat-scale models. This is achieved by incorporating the simulation results of fiber-scale models into the pleat-scale models, using the permeability coefficient and particle capture function of the porous media in the pleat model. From the fiber-scale model, it is found that the bulge zone is beneficial to improving quality factor as it could lead to a lower pressure drop. However, for the pleat-scale model, the indentation zone has a lower pressure drop than the bulge zone, resulting in a higher quality factor. This contradicts the findings of the fiber-scale model. For real applications, it has been found that pleating with indentation is more beneficial for filter performance compared to pleating with bulges. These findings help us better understand the pleating effect on filter performance and provide guidance on optimal pleating approaches.

Stress distribution model for the entire plastic zone of conical indentation with power-law hardening materials

<p indent="0mm">The classical contact mechanics provides an elastic conical indentation solution, and verifies that the strain field of elastic-plastic indentation with an arbitrary blunt indenter mostly satisfies the expanding cavity model. This study reviews the stress solution of the elastic zone for conical indentation using power-law hardening materials derived from predecessors based on the expanding cavity model and elastic-plastic mechanics. Furthermore, the expression of von-Mises equivalent stress in the plastic zone of conical indentation is determined according to the plastic stress solution of an internally pressurized thick spherical shell. The numerical verification revealed that the calculated equivalent stresses via finite element analysis are consistent with the theoretical solution of the elastic zone for conical indentation. However, a clear deviation in the entire plastic zone for the power-law hardening materials is still observed. Furthermore, to accurately describe the equivalent stress in the entire plastic zone of conical indentation for power-law hardening materials, a novel model for the indented stress distribution is established by combining the dimensional analysis method and finite element simulation. Finally, the stress model was verified using a wide range of ductile materials. The comparison results revealed that all of the calculated equivalent stresses are consistent with the model predictions for the entire plastic zone.

Star Crack Formation via Low-Velocity Impact on Glass Windows

The resistance to crack formation induced by gravel impacts on laminated glass windshields is a crucial issue for windshield manufacturers. It is proposed to study the star crack formation on polyvinyl butyral (PVB) laminated glass by designing a new highly-instrumented device that can break the glass under dynamic loading. The set-up is composed of a spring-loaded projectile that mimics a gravel momentum and an input bar equipped with strain gauges, whose end is an indenter initially in contact with the laminated glass sample. A synchronized high-speed camera allows for the observation of the crack growth. A unidimensional model introduces the local non-linear behavior of the indented zone. Crack monitoring synchronized with the Force and Velocity measurements are presented. Live-indentation depth measurements are performed. Experimental results are used in a dynamic simulation to analyze the non-linear damage behavior under the indenter tip. Dynamic and well-instrumented indentation experiments on the laminated glass are performed to investigate the star-shaped crack formation and describe the indented zone. This work is a prelude to the crack length prediction on windshields submitted to gravel pitting.

Influence of the Grain Size of ZrO2(Y2O3) Ceramics on the Hardness, Fracture Toughness and Formation of a Transformation-Deformation Relief in the Indentation Zone

Influence of the Grain Size of ZrO2(Y2O3) Ceramics on the Hardness, Fracture Toughness and Formation of a Transformation-Deformation Relief in the Indentation Zone

Laser ultrasound imaging of mechanical stresses near holes and indented areas: Experimental results and theoretical model

Experimental results on the behavior of laser ultrasonic signals near holes in stressed ceramics and metals are presented. The data obtained are analyzed within the framework of the standard theory of thermoelasticity. It is shown that this approach is not able to explain the behavior of laser ultrasonic signals in stressed materials. A new model of thermoelasticity taking into account thermal perturbation of non-stationary defect states with relaxation is presented and analyzed. It is demonstrated that strong stress dependence of the laser ultrasonic signals provides an opportunity to estimate mechanical stresses in different materials. An example of mechanical stress effect on the laser ultrasonic image near Rockwell indentation zones in metals is presented.

Large-scale programmable assembly of functional micro-components for advanced electronics via light-regulated adhesion and polymer growth

Large-area, programmable assembly of diverse micro-objects onto arbitrary substrates is a fundamental yet challenging task. Herein a simple wafer-level micro-assembly technique based on the light-triggered change in both surface topography and interfacial adhesion of a soft photo-sensitive polymer is proposed. In particular, the light-regulated polymer growth creates locally indented and elevated zones on the stamp surface. The light-mediated adhesion reduction, on the other hand, facilitates the inks to be released from the polymer. The interplay of these two effects makes it feasible for the programmable assembly of ultra-small components onto various substrates coated with supplementary adhesive layers. The fidelity of this technique is validated by assembling diverse materials and functional devices, with the printing size up to 4-inch. This work provides a rational strategy for large-scale and programmable assembly of diverse delicate micro-objects, bypassing the common issues of some existing techniques such as poor transfer uniformity, small printing area, and high cost.

Structural Peculiarities of Growth and Deformation of Ti-Al-Si-Cu-N Gradient-Laminated Coatings Due to Indentation

The composition, structure, properties and deformation behavior during the indentation of gradient-layered heterophase coatings of a Ti-Al-Si-Cu-N system were studied using scanning, transmission microscopy and hardness measurement techniques. The results showed the alteration of structural state characteristics—decreased crystal sizes and crystal lattice parameter and increased lattice bending–torsion—throughout the coating thickness, which changed depending on the elemental composition and the synthesis conditions. The work also studied the coating’s fracture behavior and assessed the macroscopic plastic deformation of its separate layers. It was established that near the indenter’s tip, the nanocrystalline structure experienced the formation of separate nanosized localized fracture areas that were connected by multiple branching cracks. It was shown that the deformation of nanocrystalline and submicrocrystalline layers may exceed dozens of percent, and more in magnitude, especially with increasing distance from the indentation tip in the case of a layer with a columnar structure. The characteristics of the microstructure of different coating layers in the indentation zone were studied. It was found that in the indentation zone under the indenter’s tip, the deformation of layers with initially different structures led to equalization of the characteristics of their structural state and the similarity of a defective microstructure at the nanoscale level.

New method to determine the true hardness of structural steels

The hardness of the material hardened in the zone of penetration of the indenter is recorded by standard methods of measuring hardness. This disadvantage is the main reason for the appearance of the size effect (indentation size effect) and a decrease in the measurement accuracy. The aim of the work is to develop a mechanical method for determining the hardness of metals and alloys without taking into account hardening in the zone of penetration of the indenter. Based on the linear relationship between the hardness and the resistance to deformation of the material, a formula was obtained for determining the hardness without taking into account the effect of hardening in the indentation zone, which makes it possible to increase the accuracy of mechanical methods for determining the hardness, expands their functionality and scope. The essence of the proposed method is illustrated by the example of determining the hardness of specimens made of steel 20, subjected to compression at various degrees of deformation. Compression test method was used to construct a hardening curve, which was used to determine the resistance to deformation of the material in the zone of penetration of the indenter and then the hardness of the material without taking into account the hardening in the zone of penetration of the indenter. The developed method for measuring the hardness of metals and alloys makes it possible to increase the accuracy of mechanical methods, to avoid the influence of the indentation size effect on the final result, and can be used to optimize the technologies for manufacturing parts.

Genetic Analysis of Blastocyst from Metaphase I like Oocytes with Indented Zone Pellucida

Genetic Analysis of Blastocyst from Metaphase I like Oocytes with Indented Zone Pellucida

Effect of low-dose Xe20+ ion irradiation on the deformation behavior of the magnetron sputtered Cr coatings under nanoindentation

The magnetron sputtered Cr coatings on zirconium (Zr) alloy substrates were irradiated by the 5 MeV Xe20+ ions at room temperature, followed by the studies on microstructure, mechanical properties, and deformation behavior. The coatings exhibit structural integrity without blistering or flaking effects after the 1 × 1014 ions/cm2 irradiation, but the irradiation caused the surface particle refining and the hardening effect. The hardness of the irradiated coating increased ~60% and the indentation modulus decreased ~10%. Moreover, the microstructural characterization was conducted on the tetrahedron indentations by using scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM). A piling-up of matter was observed in the indentation of the as-deposited coating, whereas some micro-cracks appeared near the indentation zones on the irradiated coatings. The cross-sectional TEM micrograph of an indentation further revealed the disordering of lattices and the bending of columns in the irradiated area, maybe for the irradiation made the column interface strong so that the column sliding hardly occurred.

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.

Exploring the origins of the indentation size effect at submicron scales

The origin of the indentation size effect has been extensively researched over the last three decades, following the establishment of nanoindentation as a broadly used small-scale mechanical testing technique that enables hardness measurements at submicrometer scales. However, a mechanistic understanding of the indentation size effect based on direct experimental observations at the dislocation level remains limited due to difficulties in observing and quantifying the dislocation structures that form underneath indents using conventional microscopy techniques. Here, we employ precession electron beam diffraction microscopy to "look beneath the surface," revealing the dislocation characteristics (e.g., distribution and total length) as a function of indentation depth for a single crystal of nickel. At smaller depths, individual dislocation lines can be resolved, and the dislocation distribution is quite diffuse. The indentation size effect deviates from the Nix-Gao model and is controlled by dislocation source starvation, as the dislocations are very mobile and glide away from the indented zone, leaving behind a relatively low dislocation density in the plastically deformed volume. At larger depths, dislocations become highly entangled and self-arrange to form subgrain boundaries. In this depth range, the Nix-Gao model provides a rational description because the entanglements and subgrain boundaries effectively confine dislocation movement to a small hemispherical volume beneath the contact impression, leading to dislocation interaction hardening. The work highlights the critical role of dislocation structural development in the small-scale mechanistic transition in indentation size effect and its importance in understanding the plastic deformation of materials at the submicron scale.

Mechanistic models to predict thrust force and torque in bone drilling: An in-vitro study validated with robot-assisted surgical drilling parameters

Compression plates are widely used in orthopaedic surgeries for internal fixation of fractured femurs. To fix the plate and thus to provide compression to a fracture, the self-tapping bone screws are tightened through predrilled pilot holes of smaller diameter. Preliminary investigation showed that the holes drilled with the inappropriate cutting parameters cause mechanical and thermal damages to the local host bone, which further lead to loosening of internal fixations. In this paper, the mechanistic models to predict the thrust forces and torques during bone drilling were developed, using a 3.20 mm diameter drill bit. As a procedure, the cutting action was investigated at three different regions of the drill point, namely cutting lips, secondary cutting edges and indentation zone. The models employed the analytical approach to account for the drill-bit geometry and cutting parameters, and an empirical approach to account for the material and friction properties. To complete the procedure, calibration experiments were conducted on bovine cortical femurs with two different spindle speeds (1000 and 3000 r/min) and feeds (0.03 and 0.06 mm/rev), and then the specific normal and friction coefficients were determined. The developed mechanistic models were validated with different ranges of parameters (500–3500 r/min speeds, and 0.02–0.07 mm/rev feeds) those commonly involved in manual and robot-assisted surgery. The validation study revealed that the thrust forces predicted using the mechanistic models showed a maximum error of only 5.80%. However, the torques predicted from the mechanistic model found with more error than the thrust forces. The predominant reasons for this under-prediction might because of the extrapolation used to determine the specific cutting pressures, slip-line field applied to the indentation zone instead of compressive fracture, and chip clogging involved during the bone drilling as demonstrated in earlier studies. Despite the deviations, the developed mechanistic models satisfactorily follow the trends of the thrust forces and torques experienced during bone drilling. The outcomes can be used to practice the bone drilling procedure and monitor the effect of process parameters on thrust forces and torques in the in-silico environment before performing actual surgery.

A phenomenological study of the influence of the hardening type on the indentation F-h cyclic curve

This paper is a phenomenological study representing the influence of the hardening type on the instrumented indentation F-h curve. Spherical instrumented indentation and inverse analysis techniques (IAT) are used and two metallic materials (DP600 and AA2017) are investigated. Pure isotropic (Voce) and combined (Chaboche 1986) hardening laws are adopted for describing the plastic behavior of the studied materials. The influence of the hardening type on the indentation loading curve is studied first. Kinematic hardening results in softening the indentation loading curve. This is due to some regions in the indented zone that undergo different loading paths during loading. Hardening types (kinematic & isotropic) should be considered to accurately characterize the mechanical behaviour of different metallic materials using indentation curves. The influence of the hardening type on the indentation unloading-reloading curve (hysteresis loop) is then studied. Kinematic hardening has an important influence on the hysteresis loop. This influence has been investigated closely and a methodology is proposed for estimating the contribution of each hardening type in the overall hardening behavior. This methodology is based on geometrical parameters directly influenced by the hardening type and presents great potential if considered in future works aiming to identify parameters of relatively complex hardening laws using the instrumented indentation technique (IIT).

Nanoindentation Induced Elastic-plastic Deformation of GaN Nanomembrane on a Sapphire Substrate

One of the main challenges of the production of a blue laser is the preparation of defect-free GaN layers. It is of high tehnological interest to characterize GaN nanomembrane mechanically for further advanced applications. The current study addresses the impact of applied stresses on GaN nanomembranes, which are placed on sapphire the substrates, using nanoindentation as a nondestructive test. The mechanical response of the 20, and 100 nm thin GaN nanomembrane were studied at different normal applied loads ranging from 1 mN down to 0.1 mN using the Berkovich nanoindentation technique. There were plastic deformation regions at the nanoindented GaN nanomembranes monitored by the load-displacement (<i>p-h</i>) curves. The depth of the deformed regions increased with increasing the applied loads on the diamond indenter. Beside the <i>in-situ</i> depth estimation of the residual nanoindentation using the instrumented nanoindentation machine, Atomic Force Microscopy (AFM) has been deployed as an <i>ex-situ</i> measurements of indentations depth. Scanning Electron Microscopy (SEM) provided us with surface images of the indented membranes. Indentation of the 100 nm thick GaN nanomembrane, where the effect of the substrate is reduced, showed discontinuity in the <i>p-h</i> curves. These discontinuity or pop-in events were attributed to a possible sudden initiation and propagation of threading dislocations in the GaN nanomembrane which was free of threading dislocation upon fabrication. It was suggested to employ μ-Raman spectroscopy methods to investigate the possible structural phase transformation of thicker GaN nanomembranes and to measure the compressive or tensile stresses within the center of the indented zones. Where the observed sudden load-displacements discontinuity or depth excursions during indentation of GaN nanomembranes can be attributed.

The Ultimate Load Estimation of Welded Joints of High-Strength Steels subject to Mechanical and Geometric Heterogeneity

In this paper we consider the problems arising in the numerical estimation of the ultimate load of welded joints of high-strength steels with slight hardening. The stress concentrator in the transition node from the deposited to the base metal is modeled based on the example of welding a roller wire on a plate made of high-strength steel. The use of welding wire with a yield point lower than that of the base metal allowed to simulate areas of the welded joint with heterogeneous mechanical properties. The geometry of three areas of the welded joint is studied, i.e. weld metal, heat-affected zone (HAZ) and the base metal. Mechanical properties of all three areas are determined by calculation and experimentally. For this purpose, it is proposed to consider the material in all sections as ideally elastic-plastic, and the yield strength is uniquely associated with the hardness in the indentation zone (a Rockwell diamond cone is used). Calculations of the inelastic indentation process by the finite element method (FEM) in axis-symmetric formulation allowed obtaining a linear relationship between the hardness and the yield strength with a coefficient of 0.418. Tests at a quasi-static three-point bend (with stretching in the surfacing area) were carried out on sample beams cut perpendicular to the direction of welding. The “force-deflection” diagrams are obtained and compared with the calculated curves (FEM in a three-dimensional formulation with an explicit consideration of the complex configuration of all sections and different yield stress in the areas determined by local hardness values). There is a good agreement between the calculated and experimental ultimate loads. The proposed method of the three-stage study (determination of local hardness, yield strength in the areas and the ultimate load) can be effectively used to assess the ultimate loads of the welded joints due to the low parametricity of the proposed models of materials inelastic deformation in areas for which it is impossible to manufacture standard samples for the study of mechanical properties. The experimental study of the strengthening effect of the seam with a stress concentrator in the form of an angle of 90 degrees on the value of the ultimate bending load showed that the removal of the deposited metal does not lead to an increase in the ultimate load of the welded joint when using the welding wire of low-carbon high-plastic steel.

Fracture Resistance of Brittle Materials Under Local Loading by Scratching to Edge Chipping. Part. 1. Methodical Grounds of Research

Methodical aspects of experimental investigation of brittle materials under local edge loading by scratching the specimen surface with a Rockwell indenter to its edge chipping (S+EF method) are detailed. The edge damage parameter range (fracture distance) had its basis in the literature data on numerical simulation of the stress-strain state in the local indentation zone of the material surface to its edge chipping. Fractographic analysis of tested edges revealed their damage behavior under given loading conditions. The paths of fracture crack propagation to the formation of “shell-like” chip scars, which are asymmetric quasi-conical crack traces, are studied. Partially formed or strained chips having a somewhat distorted fracture surface as compared to the “ideal” geometry of the edge chip were also found. The asymmetry of chip scars was established to have no effect on the fracture resistance of the material. The validity of empirical investigation results was achieved with a minimum test scope, determined by statistical data processing. This test method of low material intensity can be effectively applied to different lines of research.

Indentation of bituminous coals: Fracture, crushing and dust formation

Bituminous coals are still the main source of energy in the world. However, these brittle porous materials are prone to crushing under action of industrial tools. Our early depth-sensing nanoindentation tests of bituminous coals showed that even if the depth of indentation is within the nanoscale, these brittle coals are no longer continuous elastic media within the indentation zone but rather fine powders of crushed particles irrespectively to the coal maceral. Dust formation of the materials is a problem of great practical importance for the mining industry. Indeed, the powders of coal particles formed during crushing may cause not only explosions in mines but they also contaminate the environment around the roads of the coal transportation. In this study, the crushing of coals due to action of rigid conical indenters and formation of small coal particles is investigated. The studies are based on development of the Galanov-Grigoriev (GG) model of crushing of brittle porous materials and the model adjustment to specific features of coal fracture. Using the indentation tests, we estimate the size distribution of the dust particles formed within the region of fully crushed material. Results are presented for coals of three different stages of metamorphism.

Temperature effect on mechanical response of c-plane monocrystalline gallium nitride in nanoindentation: A molecular dynamics study

A series of three-dimensional molecular dynamics (MD) simulations was performed to investigate the effect of temperature on the nanoscale deformation behaviour and mechanical properties of c-plane monocrystalline gallium nitride (GaN) under nanoindentation. Simulation results showed that the atomic displacement and strain increased with increasing temperature. Thus, the nucleation and propagation of dislocations in the main slip systems were promoted to intensify the plastic deformation of GaN crystal. Increasing the temperature also contributed to the increase in local phase transition from the wurtzite crystal structure (B4-GaN) to the zinc-blende crystal structure (B3-GaN) and a very evident amorphization of GaN in the indentation zone. Based on the analysis of the load-depth curves, it was found that both the hardness and Young's modulus decreased as the temperature increased. This work can enrich the atomic-level understanding of the effect of temperature on the mechanical response of monocrystalline GaN when subjected to the external loads.

Dissimilar joining of Al/SS sheets with interlayers by ultrasonic spot Welding: Microstructure and mechanical properties

Ultrasonic spot welding (USW) has received a great deal of attention by the automobile manufacturer to build lightweight structural components. However, the versatility of using this process is still limited due to the substantial instabilities in weld quality. These fluctuations are mainly due to the lack of scientific understanding of this process and poor control of intermetallic compound formation. Therefore, this study is focused on the improving of the joint strength and its quality by ultrasonic welding of Al3003 and SS304 sheets with molybdenum (Mo) and zinc (Zn) powder as interlayers. The results revealed that the optimum thickness for Mo and Zn interlayers are found to be 0.11 mm and 0.15 mm, respectively. In comparison, Al3003/SS304 joints with Zn interlayer exhibits the maximum tensile shear failure load about 626.44 N at 1.5 s of weld time, which is better than those of the joints produced with Mo interlayer. The microstructural morphologies at the weld interface reveal the different characteristics like mechanical interlocking at the outside zone of the sonotrode knurl indentation, wavy type region under the sonotrode knurl, and swirling like diffusion zone inside the sonotrode knurl.