Stages Of Indentation Research Articles

Slip responses and pre-twin structure evolution based on indentation pile-up in magnesium single crystal

Slip behavior and microstructure evolution caused by the indentation pile-up deformation were studied in Mg single crystal with {10–12} pre-twin structure at room temperature. The anomalous indentation is formed on the surface of the large-size single crystal. It is attributed to plastic flow induced by the combined effects of dislocation slip, detwinning and {10–12} twinning during indentation. At the early stage of indentation, basal slip dominates the pile-up deformation. And the reaction structure of basal slips, i.e. (0001) slip plane in the twin to correspond to (0001) slip plane in the matrix, is frequently formed on the twin boundary in order to facilitate plastic relaxation of the local stress on the twin boundary. Under pile-up pattern, the stress state favors detwinning. And detwinning behavior is subjected to effects of stress-field magnitude and pre-twin size. For the little-volume and large-volume pre-twins, detwinning behaviors play the modes of twin shrinkage and “local detwinning” respectively. The latter might involve reverse nucleation and growth of matrix. Although pile-up pattern is unfavorable to {10–12} twinning, stress concentration caused by the interaction between slip dislocations and twin boundary induces the local twin growth on the interface. In addition, a pyramidal slip is found in matrix, and its slip trace is corresponding to (0001) slip trace in twin.

Mechanical Response of Cu/Sn58Bi-xNi/Cu Micro Solder Joint with High Temperatures

Sn58Bi solder is considered a promising lead-free solder that meets the performance requirements, with the advantages of good wettability and low cost. However, the low melting point characteristic of Sn58Bi poses a serious threat to the high-temperature reliability of electronic products. In this study, Sn58Bi solder alloy based on nickel (Ni) functionalization was successfully synthesized, and the effect of a small amount of Ni on creep properties and hardness of Cu/Sn58Bi/Cu micro solder joints at different temperatures (25 °C, 50 °C, 75 °C, 100 °C) was investigated using a nanoindentation method. The results indicate that the nanoindentation depth of micro solder joints exhibits a non-monotonic trend with increasing Ni content at different temperatures, and the slope of the indentation stage curve decreases at 100 °C, showing that the micro solder joints undergo high levels of softening. According to the observation of indentation morphology, Ni doping can reduce the indentation area and accumulation around the indentation, especially at 75 °C and 100 °C. In addition, due to the severe creep phenomenon at 100 °C, the indentation hardness rapidly decreases. The indentation hardness values of micro solder joints of Cu/Sn58Bi/Cu, Cu/Sn58Bi-0.1Ni/Cu, and Cu/Sn58Bi-0.2Ni/Cu at 100 °C are 14.67 ± 2.00 MPa, 21.05 ± 2.00 MPa, and 20.13 ± 2.10 MPa, respectively. Nevertheless, under the same temperature test conditions, the addition of Ni elements can improve the high-temperature creep resistance and hardness of Cu/Sn58Bi/Cu micro solder joints.

In situ TEM observations and molecular dynamics simulations of deformation defect activities in Mg via nanoindentation

In this work, we performed in situ nanoindentation in TEM to capture the real-time 〈c + a〉 dislocation and twinning activities in pure Mg during loading and unloading. We demonstrated that the screw component of 〈c + a〉 dislocations glides continuously, while the edge components rapidly become sessile during loading. The twin tip propagation is intermittent, whereas the twin boundary migration is more continuous. During unloading, we observed the elastic strain relaxation causes both 〈c + a〉 dislocation retraction and detwinning. Moreover, we note that the plastic zone comprised of 〈c + a〉 dislocations in Mg is well-defined, which contrasts with the diffused plastic zones observed in face-centered cubic metals under the nanoindentation impressions. Additionally, molecular dynamics simulations were performed to study the formation and evolution of deformation-induced crystallographic defects at the early stages of indentation. We observed that, in addition to 〈a〉 dislocations, the I1 stacking fault bounded with a 〈1/2c+p〉 Frank loop can be generated from the plastic zone ahead of the indenter, and potentially serve as a nucleation source for abundant 〈c + a〉 dislocations observed experimentally. These new findings are anticipated to provide new knowledge on the deformation mechanisms of Mg, which are difficult to obtain through conventional ex situ approaches. These observations may serve as a baseline for simulation work that investigate the dynamics of 〈c + a〉 dislocation slip and twinning in Mg and alloys.

Film failure at earlier and later stages of nanoindentation in static and sliding modes

Crack growth needs to be restricted in ceramics used for biomedical, microelectronic, and any structural applications whatsoever. Having the know-how of its initiation and propagation will save the material from getting fractured. For materials used in high-precision applications, nanoindentation (static) and scratch tests (sliding) serve the purpose of meticulous investigations of understanding crack propagation. The fractographic analysis of the hard ceramic coating of SiCN on silicon substrates has been given in this communication. The pertaining factors like residual stress, geometry, and elastoplastic deformations were correlated. Finite Element Analysis provided insights into the chronological stress distribution. Parameters like stress intensity factors and interfacial fracture energy were determined. It was found that the initiation of coating failure has its roots in much earlier stages of indentation.

An experimental and numerical study on the wear mechanism of cutters on workover bits under thermo-mechanical coupling

The workover bit is the core tool for removing mental junk in the wellbore and determining construction efficiency. In order to solve technical bottlenecks of slow footage and fast wear, a thermo-mechanical coupling analytical model of cutter on workover bit was proposed based on the principle of the heat source method, which clarified the quantitative relationship between temperature, structure, and physical parameters. Also, a thermo-mechanical coupling 3D numerical model of cutter was proposed by the penetration contact algorithm of temperature-displacement coupling, which revealed the chip formation mechanism and distribution characteristics of high-temperature areas. Besides, as the severe conditions of insufficient cooling of workover bits, the non-cooling milling experiment of the workover bit with single cutter was carried out. Then the wear morphology characteristics and wear mechanism under the action of thermo-mechanical coupling were explored. The results show that the temperature error of the thermo-mechanical coupling numerical model of cutter is within 13.0%, which meets the accuracy requirements of basic engineering analysis. Under the action of thermo-mechanical coupling, the workover bit produces roll-shaped chips with a curvature radius of 2.03 mm. The high-temperature area of cutter is distributed on the outside of the cutting edge. In the meanwhile, the temperature on the rake face of cutters has the fastest increase and the highest temperature, and the highest temperature can reach 541.6 °C. The wear mechanism of cutter can be divided into four stages: gradual indentation stage, mechanical wear stage, bond wear stage, and high-temperature oxidation stage. When milling continuously for 5 min, the wear volume of the cutter reaches 0.51 mm3, and controlling temperature is the key to reducing the wear of the cutter. This research can provide theoretical guidance and a scientific basis for revealing the wear mechanism and prolonging the service life of workover bits.

Effect of Ball Burnishing Pressure on Surface Roughness by Low Plasticity Burnishing Inconel 718 Pre-Turned Surface.

The low plasticity burnished surface roughness is significantly affected by the low plasticity burnishing (LPB) parameters. This research proposed the analytical prediction model to predict the LPBed surface roughness and optimal LPB pressure based on Hertz contact mechanics and the slip-line field theory. In this study, the surface formatted process was divided into the smoothing stage (SS) and the indentation stage (IS). The smoothing mechanism of SS and the deterioration mechanism of IS were analyzed theoretically. The analytical prediction model for the LPBed surface roughness was proposed based on Hertz contact mechanics and slip-line field theory. The proposed analytical prediction model was validated by the LPBed surface roughness of AISI 1042, and the error of the analytically predicted results was less than 13.3%. After validation, the proposed model was applied to predict the LPBed surface roughness of Inconel 718. The single-factor experiments were conducted. The error between the proposed model prediction results and experimental results was less than 7% for the LPBed surface roughness of Inconel 718. The optimal LPB pressure interval was calculated to be [12.2 MPa, 17.5 MPa], corresponding to the experimental one as [12 MPa, 18 MPa]. It indicated that the proposed model could accurately predict the LPBed surface roughness and conduct the LPB processing.

УЧЕТ ТРЕНИЯ НА НАЧАЛЬНОМ ЭТАПЕ ВЕРТИКАЛЬНОГО ВНЕДРЕНИЯ ВЫПУКЛОГО УДАРНИКА В УПРУГУЮ ПОЛУПЛОСКОСТЬ

The initial stage of indentation of a convex rigid punch into isotropic elastic half-plane with friction is considered. A closed mathematical formulation in Cartesian coordinates is presented by equations of motion in the absence of a body force for homogeneous isotropic elastic medium in terms of displacement potentials, Cauchy equations for deformations, Hooke law and translational equation for the punch. Initial conditions are homogeneous. Outside of contact region surface is free from stresses. Inside contact region normal displacements of the surface of a half-space and the surface of a punch are taken to be equal and the relation between tangential and normal stresses in a form of Coulomb friction law is given. Due to the short duration of the supersonic stage and smallness of the contact region radius the tangential stress direction is considered to be point independent. Resolving functional equations are given in a form of convolutions with influence functions. The latter is the solution the original problem for half-plane with a special boundary condition in a form of the Dirac delta function. This solution is obtained in the domain of Laplace transform by time and Fourier transform by spatial coordinate. The original is constructed with the combined Fourier–Laplace inversion method. Solution is given with consideration to the initial stage characteristic property of supersonic velocity of contact region expansion (no smaller than propagation velocity of expansion-compression waves). It is shown that kinematic parameters of the punch, resulting force and discontinuities of the first kind on boundaries of the contact region are independent of friction unlike contact pressure. Calculation examples for different values of friction coefficient are presented.

Study on damage evolution beneath spherical indenter through experiments and mechanism-based strain gradient crystal plastic simulations

Damage evolution of AA7075-T6 rolling plate with 2 mm thickness under highly compressive stress state, which is generated by spherical indentation, is studied through experiments and simulations. On the cross section of spherical deformation region, micro voids induced by crush of MgZn2 particles are observed by scanning electron microscopy (SEM) and some special characteristics are revealed including ductile tearing of the brittle particle, huddling between neighboring voids and an in-void crack, but no clue of void closure under such heavy compression. Through Electron Back-Scattered Diffraction (EBSD), strain gradient around void was found quite high (70 mm−1) and much higher than the theoretical strain gradient induced by spherical indentation (1.8 mm−1), which will result in a significant hardening effect and preventing the further shrink and closure of micro void. More insights are provided through mechanism-based strain gradient crystal plastic simulations which couples a polycrystalline, full-scale model, and a single crystal submodel. Simulation results verify the elevated strain gradient around microvoid and find strain gradient varies dramatically along the small range of void edge, which is validated by nanoindentation test around the edge of voids. Microvoid evolution controlled by strain gradient shows strong anisotropy on different cross sections. For the void at position D focused in present paper, its area on section perpendicular to Y axis (SecY) increases at the early stage of indentation, despite the compressive stress state. Influence of the orientations of adjacent grains is also studied. Void areas on SecZ and SecY are found more sensitive to the change of orientation of adjacent grain, however, the volume variation show much less sensitivity.

Atomic force microscopy nanoindentation kinetics and subsurface visualization of soft inhomogeneous polymer.

Modern techniques of nanoindentation by atomic force microscopy (AFM) produce maps of topography and physical-mechanical properties of the material. Analysis of the interaction rate of the AFM tip with the soft surface reveals the surface and subsurface structure and expands standard analysis of the material behavior. Phase-separated polymer (polyurethane, elastic modulus-6MPa) is studied. Reversible inelastic changes of the surface at different stages of indentation were established in dependence on peculiarities of velocity and position of the AFM-tip in the material: uniform soft nanofilm covering the outer surface gradually passes into fibrillar heterogeneous structure of the polymer. The point of stable mechanical contact is defined, and the elastic moduli of soft and hard blocks of the polymer are estimated using certain intervals of the indentation. The presented methods of surface analysis are useful in the study of a wide class of soft heterogeneous materials.

Dynamic response of sandwich beam with star-shaped reentrant honeycomb core subjected to local impulsive loading

The star-shaped reentrant honeycomb produces lateral shrinkage but also rotation under compression. With the consideration of such interesting deformation characteristics, the dynamic deformation evolution of the sandwich beam with star-shaped reentrant honeycomb core (SSRHC) was carried out for the first time. In this experiment, the aluminum foam projectile was used to produce local impulsive loading on the sandwich beam to research failure/deformation modes and deformation evolution of the SSRHC. The experimental results demonstrated the simultaneous shrinking and rotating deformations in the core. Finite element model (FEM) was employed to capture the dynamic mechanical response of panels and SSRHC on account of experimental results. Numerical results illustrated that the face panel moved toward the loading area in the early stage of impact, and local shrinkage or expansion was found within different regions of the star honeycomb cores during the entire compression process. In addition, it was found that the rotational deformation of the star honeycomb cells mainly occurred in the local indentation stage of the sandwich beam.

The effect of grain boundary on the local incipient plastic deformation of fcc metals during nanoindentation

The effect of grain boundaries (GBs) on deformation mechanisms becomes increasingly important as the volume of deformation reaches the submicrometer and nanoscale. The current work investigates the impact of grain boundaries on the incipient plasticity of small-scale deformations of fcc metals. For this purpose, the behavior of single and bi-crystal Au thin films during nanoindentation are studied, using large-scale atomistic simulations. Various symmetric ⟨110⟩ tilt GBs with a wide range of misorientation angles are included to analyze the effect of GB geometry on the nanoscale plasticity mechanisms. Potentially, GBs can act as a source, sink, or obstacle for lattice dislocation, depending on their geometry, energy level, and distance from the deformation zone. The role of the heterogeneous nucleation and emission of dislocations from GBs on the plasticity and hardness of bicrystals is analyzed. According to our results, the intrinsic free volume involved in the GB region is associated with dislocation nucleation at the GB. The volume of the plastic zone generated beneath the tip and the way it grows is strongly dependent on the GB structure. Dislocation nucleation occurs predominantly in the early stages of indentation at GBs with a dissociated interface structural unit, before the interaction of lattice dislocation and GB. Coherent twin boundaries display the lowest effect on the hardness. Based on our results, there is a strong correlation between the interfacial boundary energy and its effect on the bicrystal hardness. GBs with lower interfacial energy offer a higher barrier against slip transmission and nucleation at the GB.

Specialties of deformation and damage of the topocomposite on a ductile substrate during instrumental indentation

We studied the nature of deformation and damage of topocomposites with instrumental indentation. The topocomposite is considered as a layered system consisting of a solid thin coating coherently bonded to a substrate of a ductile solid material. The object of the study is a topocomposite that consists a coating of titanium nitride deposited by magnetron sputtering in vacuum on a substrate of aluminum alloy. Comparing the balance of energy spent at all stages of indentation using model and experimental diagrams of indentation, the contribution of work dissipated on the deformation to the layered system, on the interfacial delamination at the coating-substrate interface and on the formation of through circular cracks in the coating is estimated. The research results can be used for a qualitative estimation of the efficiency of functional surfaces of machine parts hardened with coatings and for calculating the characteristics of deformation and damage.

An MD simulation study to the indentation size effect of polystyrene and polyethylene with various indenter shapes and loading rates

Abstract Several nanoindentation MD simulations were conducted to investigate the indentation size effect (ISE) of Polystyrene (PS) and Polyethylene (PE) at nano-scale using different indenters and loading rates. A strain gradient elasticity model in which the ISE is related to the Frank energy caused by finite bending stiffness and neighboring interactions of chains was imported to describe the ISE in this work. Two large-scale molecular substrates for PS and PE were constructed to compare the ISE performance during indentation simulations. The spherical indenter was firstly considered, and an uptrend of the calculated hardness and modulus with increasing indenter radius was found for both PS and PE. A conical indenter consisting of 25 virtual rigid spheres used in LAMMPS was designed. Considering different tip sizes and loading rates, indentation simulations using these conical indenters were conducted. The uptrend of hardness curves at the initial indentation stage was also found in conical cases. Through fitting the hardness curves, the strengthening effects of tip size and loading rate were certified, especially for PS. At nano-scale, the dominant effect of benzene ring component on ISE performance was confirmed. The downtrend of ISE was found to exist at nano-scale for PE although it was not obviously found in experimental cases and the contributing factors for this kind of ISE were discussed.

Indentation Characteristics Using Various Indenters: A Study Based on Laboratory and Numerical Tests

Laboratory and numerical indentations, using wedge-shaped, spherical and blunt indenters, were performed. The laboratory and numerical results agreed well that fluctuations of the indentation force occurred after the peaks. In addition, indentations by the wedge-shaped indenter generated median cracks whereas, for the spherical and blunt indenters, median and lateral cracks formed. We inferred from the numerical study that the fluctuations correlate to the crack propagation. In addition, the subsequently concentrated tensile stress zones are responsible for the generation of the median and lateral cracks, caused by spherical and blunt indenters. However, for the wedge-shaped indenter, the tensile concentrated zone, forming at the early indentation stage, can cause the median crack.

Indentation response of nanoporous gold from atomistic simulations

Abstract

The problem solution on wedge penetration in an initially anisotropic medium within the rigid-plastic scheme

Two problems are solved in the paper: on ultimate loads in the initial stage of indentation of an absolutely rigid smooth wedge into a layer of an initially anisotropic plastic medium and in the final stage when the tool penetrates through the layer. The problems are solved with Chanyshev’s constitutive relations of plasticity of the initially anisotropic medium based on use of the eigen elasticity tensors.

A fracture mechanics model to study indentation cutting

AbstractMany cutting processes, such as chopping, slicing, and carving, consist in 2 different stages: an initial stage of indentation, in which the cutting tool is pushed into the material under the action of an external force, and a second stage, where the target material undergoes a progressive separation. This second stage is characterised by the formation of a fracture surface followed by the cut propagation due to the increasing external force, until eventually a steady state might occur. The purpose of this paper is to analyse the cutting process by means of some concepts of fracture mechanics and discuss the occurrence of the steady state. A simple model is used to obtain an analytic expression of the stress intensity factor at the tip of the cut and investigate the evolution of the fracture process. It is found that the cut propagation depends on the wedge sharpness. The analytic results are compared with finite element analyses, where the effect of tip blunting due to plasticity is taken into account. The influence of the cutting tool geometry is also discussed.

Numerical simulation of GLARE 4A fiber-metal laminates subjected to ballistic impact

This article deals with the evaluation of the ballistic resistance of GLARE 4A fiber-metal laminates subjected to high velocity impact by a cylindrical projectile. Important impact variables such as the ballistic limit, the impact load and the absorbed energy time histories are predicted using the ANSYS LS-DYNA software. The simultaneous existence of various impact damage mechanisms, which is unique in fiber-metal laminates, is demonstrated using the numerical results. Each of the mechanisms absorbs a part of the initial impact energy and contributes to the high ballistic impact resistance the materials. With reference to the considered GLARE 4A panels, the behavior of the transient impact load is analyzed and useful conclusions are drawn. It is found that the maximum impact load is applied at the beginning of ballistic impacts, during the initial local indentation of the panels under the projectile. It is substantially higher than the following peak values of the impact force time history. It is revealed that during the beginning of ballistic impacts, the impulse of the collision increases as the thickness of the panels is increased. The work done by the impact load during the local indentation stage is also an increasing function of the panels’ thickness.

Dynamic Indentation Characteristics for Various Spacings and Indentation Depths: A Study Based on Laboratory and Numerical Tests

Laboratory and numerical study tests were conducted to investigate the dynamic indentation characteristics for various spacings and indentation depths. First, laboratory tests indicate that the increase in the indentation depth first resulted in enlarged groove volumes, caused by fiercer rock breakages between indentations for a fixed spacing; then, the groove volume slightly increased for further increase in indentation depth, whereas the increase in spacing restrained rock breakages and resulted in shrunken grooves. In addition, the numerical study agreed well with laboratory tests that small chips formed at the shallow part of the rock specimen at the early indentation stage, and then, larger chips formed by the crack propagation at deeper parts of the rock specimens when the indentation depth increased. With further increase in indentation depth, crushed powders instead of chips formed. Moreover, the numerical analysis indicates that crack propagation usually leads to the decrease of the indentation force and the dissipation of the stress concentrations at crack tips, whereas the cessation of crack propagation frequently resulted in the increase of the indentation force and the stress concentrations at crack tip with the increase in indentation depth.

Analysis of the mechanical response of biomimetic materials with highly oriented microstructures through 3D printing, mechanical testing and modeling

Many biomineralized organisms have evolved highly oriented nanostructures to perform specific functions. One key example is the abrasion-resistant rod-like microstructure found in the radular teeth of Chitons (Cryptochiton stelleri), a large mollusk. The teeth consist of a soft core and a hard shell that is abrasion resistant under extreme mechanical loads with which they are subjected during the scraping process. Such remarkable mechanical properties are achieved through a hierarchical arrangement of nanostructured magnetite rods surrounded with α-chitin. We present a combined biomimetic approach in which designs were analyzed with additive manufacturing, experiments, analytical and computational models to gain insights into the abrasion resistance and toughness of rod-like microstructures. Staggered configurations of hard hexagonal rods surrounded by thin weak interfacial material were printed, and mechanically characterized with a cube-corner indenter. Experimental results demonstrate a higher contact resistance and stiffness for the staggered alignments compared to randomly distributed fibrous materials. Moreover, we reveal an optimal rod aspect ratio that lead to an increase in the site-specific properties measured by indentation. Anisotropy has a significant effect (up to 50%) on the Young’s modulus in directions parallel and perpendicular to the longitudinal axis of the rods, and 30% on hardness and fracture toughness. Optical microscopy suggests that energy is dissipated in the form of median cracks when the load is parallel to the rods and lateral cracks when the load is perpendicular to the rods. Computational models suggest that inelastic deformation of the rods at early stages of indentation can vary the resistance to penetration. As such, we found that the mechanical behavior of the system is influenced by interfacial shear strain which influences the lateral load transfer and therefore the spread of damage. This new methodology can help to elucidate the evolutionary designs of biomineralized microstructures and understand the tolerance to fracture and damage of chiton radular teeth.