Wedge Indentation Research Articles

Cutting failure behavior of foam core sandwich plates

During the ship, collisions with reefs or grounding may cause damage to the hull of ships made of sandwich plates. The cutting failure mechanism of sandwich panels is still not fully understood. In this paper, the failure behavior of metal foam sandwich plates under cutting load by a wedge-shaped indenter is studied through analytical, experimental, and numerical methods. An analytical model is proposed to describe the cutting failure behavior of foam core sandwich plates. Based on experimental results, three distinct failure modes of foam sandwich plates with varying thicknesses are observed. Numerical simulations are performed, and analytical and numerical results capture experimental results reasonably. The effects of core thickness, face-sheet thickness, and tip angle and cutting angle of wedge indenter on the failure mode, load-carrying capacity and energy absorption performance of the sandwich plates are explored. The present analytical model can effectively predict the cutting failure behavior of sandwich plates.

High-resolution measurement of contact stresses and friction in indentation and machining by full-field photoelasticity

An experimental study has been made of the sliding plastic contact in wedge indentation and machining of ductile metals. The use of full-field photoelasticity has allowed direct determination of interface pressure and shear stress distribution along the tool (indenter) and workpiece sliding contact at micron-scale resolution. Sapphire, a transparent photoelastic material that possesses sufficiently high hardness to indent and machine metals, is used as the tool material. It is shown that the Coulomb friction model applies only at the edges of the contact where the interface pressure falls below a certain value associated with the material's flow stress. Within the plastic contact zone, the mode of friction as well as the relationship between interface pressure and shear stress are very complex. In both cases, it is shown that shear stress neither remains constant nor varies in proportion to the pressure. It is proposed that the complex nature of friction and stress field at the sliding contact can be understood through simultaneous observations of the metal plastic flow at and near the interface. Using in situ measurements of the velocity field near the interface and local stress distribution at the contact from photoelasticity, friction contribution to the overall work is calculated and shown to be substantial (greater than one-third) in the case of machining.

Wedge indentation of elastoplastic solids — from single indentation to interaction between indenters

Wedge indentation of elastoplastic solids — from single indentation to interaction between indenters

Experimental characterization and finite element investigation of SiO2 nanoparticles reinforced dental resin composite

In this study, a commercial dental resin was reinforced by SiO2 nanoparticles (NPs) with different concentrations to enhance its mechanical functionality. The material characterization and finite element analysis (FEA) have been performed to evaluate the mechanical properties. Wedge indentation and 3-point bending tests were conducted to assess the mechanical behavior of the prepared nanocomposites. The results revealed that the optimal content of NPs was achieved at 1% SiO2, resulting in a 35% increase in the indentation reaction force. Therefore, the sample containing 1% SiO2 NPs was considered for further tests. The morphology of selected sample was examined using field emission scanning electron microscopy (FE-SEM), revealing the homogeneous dispersion of SiO2 NPs with minimal agglomeration. X-ray diffraction (XRD) was employed to investigate the crystalline structure of the selected sample, indicating no change in the dental resin state upon adding SiO2 NPs. In the second part of the study, a novel approach called iterative FEA, supported by the experiment wedge indentation test, was used to determine the mechanical properties of the 1% SiO2-dental resin. Subsequently, the accurately determined material properties were assigned to a dental crown model to virtually investigate its behavior under oblique loading. The virtual test results demonstrated that most microcracks initiated from the top of the crown and extended through its thickness.

Room-temperature strength of the interfacial bond between silica inclusions and iron

The strength of the interface between iron (Fe) and individual spherical silica (SiO2) inclusions of 5 ± 1 µm diameter is measured by means of in-situ micro-cantilever bending tests conducted under displacement control within a scanning electron microscope, using a wedge indenter tip. Attention is paid to ensure that reported data are not affected by either the electron beam during in-situ testing or by focused ion beam milling, used to produce the cantilevers. For the latter, a simple yet effective strategy, validated using finite element modeling, is devised to shift the peak interfacial stress towards the beam center, thereby relocating the fracture initiation position away from potential FIB-induced artefacts at the beam edge. All bend beams tested fractured along the Fe/SiO2 interface, with no visible evidence of silica microcracking or iron plastic deformation. The rapidly cooled iron matrix features a submicron ferrite grain size, causing its yield strength to exceed 1 GPa. Using classical Euler-Bernoulli beam theory, the estimated Fe/SiO2 interfacial tensile strength yields values ranging from 0.9 to 2.3 GPa, proving that SiO2 inclusions are strongly bonded to the Fe matrix at room-temperature. There is, thus, potential for engineering inclusion-containing Fe-based alloys that, under monotonic loading conditions, do not compromise the mechanical integrity of the ferrous matrix.

Characteristic material behaviors in conical indentation with friction

AbstractCharacteristic material behaviors in obtuse‐angled conical indentation for elasto‐viscoplastic solids are explored and discussed. Finite element calculations are carried out for indentation of a rigid sharp conical indenter into a cylindrical body that models a pseudo‐half space, considering the friction between the indenter and the solid. Under low‐friction conditions, it is assumed that breakage of the material by the sharp tip of the indenter occurs and a new surface emerges along the contact interface during indentation. It is revealed that the load required for indentation does not necessarily reach its maximum at the perfect sticking condition, which shows a nonlinear variation from the frictionless condition to the perfect sticking condition. The increase in strain hardening and the decrease in elastic modulus relative to yield strength both reduce the difference between the required loads for different friction conditions. For perfect sticking, the indenter tip is covered by an elastically deforming material cap during indentation similarly to the case of the plane strain wedge indentation. Similarity and discrepancy between the behavior in the conical indentation and that in the plane strain wedge indentation, which is well described by the classical slip‐line field theory, are clarified in detail.

Exploring the role of the interface adhesion phenomena focusing on surface expansion distribution

This work focused on the surface expansion of the contact surface and its influence on the interface adhesion phenomena in wedge indentation of an aluminum specimen. Direct in-situ observations coupled with high-speed imaging and particle image velocimetry techniques were performed to characterize and quantify the surface expansion behavior at the contact surface. A series of experiments showed that the surface expansion distribution at the contact surface plays a pivotal role in determining the adhesion force. The quantitative relationship between the distributions of the surface expansion and adhesion force was discussed by using single-groove indenters.

Size-dependent geometrically necessary dislocation structures in single-crystalline tungsten

Wedge indentation experiments were conducted to study the depth dependence of geometrically necessary dislocation (GND) structures in single-crystalline tungsten. Single-crystalline tungsten exhibits a pronounced indentation size effect (ISE), which can be rationalized based on GNDs. The dislocation mechanisms, however, are still under debate. Due to the plane strain condition during the wedge indentation, the dislocations in the cross sections underneath indents could be analyzed based on the Nye tensor and the lattice rotations determined using transmission Kikuchi diffraction. The dislocation structures depend on the size of the indent confirming the different hardness regimes and the bilinear ISE reported recently. For shallow indents, the dislocations are rather localized at the tip of the indent, while with increasing depth the dislocation volume expands; subgrains and distinct rays of increased dislocation density form. At larger depths, the indentation-induced deformation fields exhibit characteristics similar to the kink-type shear at a stationary crack tip.Graphical abstract

Plane strain wedge indentation revisited

For a plane strain wedge indentation problem, detailed comparisons between slip-line field theory (SLFT) solutions, experimental observations and finite-element analysis results are carried out. Several past remaining questions on this problem are explored. The finite-element computations appear to account for the nature of a modified slip-line field solution (Petryk H. 1980 Journal de Mécanique Appliquée 4 , 255–282) that assumes the existence of an additional fan-shaped slip-line field just above the boundary between yielding and unyielding regions. For obtuse-angled wedges, finite-element computations show that the indentation load could be smaller for a rough wedge than for a smooth wedge. The question that was raised in the literature with respect to the reversed order of required loads for smooth and rough wedges is not necessarily a paradox. It is revealed that with increasing friction coefficient, a distinct deformation mode resembling the dead metal cap solution in the SLFT is established immediately after passing the critical friction coefficient value at which the contact mode theoretically changes from frictional sliding to perfect sticking. The profiles of the bulged-out lip material remain straight in all the finite-element computations for non-hardening materials. Nonlinearity of the lip profiles frequently observed in experiments appears in the presence of strain hardening or strain-rate sensitivity.

Theoretical analysis of local indentation by the wedge indenter for pressurised pipeline

ABSTRACT External impact is one of the potential hazards for in-service subsea pipelines. The stress concentration by external impact can create a dent that affects the pipeline's ultimate bearing capacity. In this paper, a theoretical model based on the string-on-plastic foundation is established to model the local indentation of pressurised pipelines by a wedge indenter. The effects of internal pressure and boundary conditions on the denting process are investigated. With this model, the relationship between the indenting force and the dented depth is obtained under a set of two boundary conditions. The accuracy of the new analytical models is validated by comparing them with the specification and numerical simulation model. It is believed that the new analytical models will provide theoretical guidance for maintaining the reliability and integrity of in-service pressurised pipelines.

The Problem of Wedge Indenter with Flat-Rounded Bottom Indenting Half-Plane Elastic Body

In this paper, the problem of a wedge indenter with flat-rounded bottom indenting an infinite half-plane elastic body is solved. It can be used to study the penetration force or the surface stress distribution of the cutter when the tool intrudes into an elastic body. First, a first-order continuity method is proposed to eliminate the stress singularity caused by the sharp corners of the wedge indenter with flat bottom. The two-dimensional elastic contact problem is transformed into a Riemann–Hilbert boundary value problem with discontinuous coefficients expressed in the form of complex variables. For the frictionless contact problem, the explicit analytical solution is obtained for contact stress on the half-plane surface. Furthermore, the expression of the stress potential function is also derived to solve the stress field in the half-plane. Verification indicates that the wedge indenter with flat-rounded bottom can degenerate to several well-studied shaped indenters, including the Hertz model and flat-rounded model. The model in this paper is also validated with its numerical counterpart built in the finite element program LS-DYNA. Finally, the sensitivity of different configuration parameters on the normal contact stress and interior stress field in numerical model was investigated.

Failure behavior of prismatic Li-ion battery cells under abuse loading condition - A combined experimental and computational study

Li-ion jelly rolls and prismatic battery cells were quasi-statically loaded by three different indenters: (1) Hemispherical nose punch, (2) Flat end punch, and (3) Round edge wedge. Force and displacement during indentation were measured. For the cells, voltage drop was also recorded to monitor short circuiting. The deformation/failure modes of specimens were examined and the critical force at initiation of short circuit was analyzed for the cells. Substantial differences occurred depending upon indenter shape; also loading orientation for the wedge. In all cases, short circuiting of the entire cell initiated by formation of the first jelly roll crack. Based on test loading and boundary conditions, finite element (FE) models were developed using explicit FEA code LS-DYNA. The model predictions demonstrated good agreement in terms of force-displacement responses and structural failure modes at both jelly roll and prismatic cell levels. With the validated numerical model, the original battery cell design was modified in order to alter the deformation and failure modes of the jelly roll. Three design modifications were considered: (1) Include a thin mica sheet between the first and second jelly roll layers; (2) Use thinner, but higher stiffness/strength steel to replace the aluminum alloy enclosure material; and (3) Change the enclosure material where indenter contact occurs from an aluminum alloy sheet to an aluminum alloy sandwich structure. All three indentation conditions were simulated and results were compared to the original design. The outcomes were sensitive to indenter shape, where round end wedge indentation benefitted the most. The findings have potential for improving prismatic battery cell safety by incorporating them into future designs.

Experimental and Numerical Investigation of Cutting Characteristics of PA6/PE Nylon Film Subjected to Wedge Indentation Process

In this research work, we aim to evaluate the cutting resistance and deformation of a laminated nylon film subjected to a 42o wedged indentation. One of the problems occurred in the wedge indentation process is the unstable separation and quality of the sheared profile of the worksheet. In order to reveal the effect of cutting parameters on the cutting features, the indentation experiment of 0.16 mm thickness of Polyamide-6/ Polyethylene nylon film (PA6/PE) was conducted; the cutting line force was gotten using a recording unit; the bent-up angle and sheared profile of the worksheet were observed using a high-speed camera. From the experiment results, it was found that the cutting direction was an important factor affected to the bent-up angle and cutting load response of the nylon film. Also, the effect of cutting direction (PA6-PE and PE-PA6) of the nylon film was numerically investigated.

Plane strain deformation by slip in FCC crystals

Deformation studies of a metal or alloy single crystal under plane strain boundary conditions have proved valuable for providing information on the deformation behavior of such materials under multiaxial states of stress and strain. Examples include the initiation and propagation of cracks during brittle fracture and the development of deformation textures in metal forming operations. Restrictions imposed by plane strain boundary conditions on the values of global strain components and on active slip systems by the principle of maximum plastic work confine slip to subsets of physically possible crystallographic slip system (CSS). Such ensembles produce components of global strain that independently satisfy plane strain constraints. This leads to the definition of Pseudo Slip Systems (PSS) having basis vectors formed from the resultants of corresponding basis vectors in participating CSS. Nye’s State of Dislocation tensor applied at both macro- and micro-structural scales describes global and local lattice rotations resulting from the geometrically necessary dislocation (GND) content. Local Nye Tensors (LNT) for each active CSS are dyadic products of their Burgers vector and a Dislocation Density Vector (DDV) describing the GND population. This vector, lying in the slip plane, has a magnitude equal to that of the local GND, and a direction given by the character of the resultant population. The Global Nye Tensor (GNT), A, is the sum of LNTs for each active CSS and expresses in global specimen coordinates the resultant Burgers vector flux from all active CSS. We demonstrate these relationships by analyzing plane strain deformation in a Ni single crystal caused by wedge indentation along a 〈110〉 direction.

Cutting characteristics of nylon-polyethylene laminated film subjected to wedge indentation and its thermal dependency

ABSTRACT This paper reports on the cutting resistance and deformation of a laminated PA6/PE (nylon-polyethylene) film stacked on a PC (polycarbonate) underlay by a wedge indentation. To investigate the effects of mechanical conditions on the cutting characteristics of the PA6/PE film, the blade tip thickness and temperature of blade were varied. The cutting line force was obtained using a recording unit; the bent-up angle and cutting profile of the PA6/PE film was observed using a CCD camera. From the experiments, it was revealed that the blade tip thickness remarkably affected the bent-up angle and quality of sheared profile of the PA6/PA film. Moreover, the effects of temperature of blade on the deformation of the PA6/PE film were revealed.

Large deformability of Mg alloys produced by confinement to the nanoscale in one dimension

ABSTRACT We report a transition to large-strain, multi-slip plasticity in Mg alloys resulting from refinement of a single dimension of the deformation geometry to the ∼ 100 nm-scale. Basal-slip-dominated strain localisation and fracture is suppressed and shear strains greater than 200% are realised at ambient temperatures when one characteristic dimension is refined in an asymmetric wedge indentation, even when the other two dimensions remain macroscopic. The ductility at sub-critical scales of low dimensionality discovered here is independent of crystal orientation, and interfaces and large shear strains result in homogeneous nanocrystallinity in the deformed material under these conditions.

Hyperelastic constitutive modeling of hydrogels based on primary deformation modes and validation under 3D stress states

In isotropic linear elasticity, a constitutive model calibrated using a single deformation mode (e.g., compression or tension or shear) is sufficient to describe a complex three-dimensional (3D) stress state. Such an approach, however, is likely inadequate for modeling hydrogels, which exhibit a nonlinear stress-strain response that varies significantly between deformation modes and is also sensitive to microstructure via gel concentration. In this study, a combined experimental and constitutive modeling framework is proposed for the development and validation of concentration-dependent 3D hyperelastic models for hydrogels. Agarose hydrogel in a concentration range of 0.4–4% w/v is chosen as the model material. Uniaxial compression, uniaxial tension, and simple shear (three primary deformation modes) experiments are conducted. The small strain elastic modulus-gel concentration relationships obtained from experiments are compared with those predicted by the molecular theory of rigid polymer networks (Jones-Marques theory) to identify the concentration range in which entropic elastic (hyperelastic) response dominates. In this range (1.5–4% w/v), four hyperelastic constitutive models are fit to the combined compression-tension-shear stress-strain data: Mooney-Rivlin, three-parameter generalized Rivlin, Gent, and Gent-Gent models. It is demonstrated that the generalized Rivlin model offers the best overall accuracy, and the variation of its model parameters with gel concentration is consistent with the Jones-Marques theory. The resulting concentration-dependent Extended Generalized Rivlin model is employed in finite element simulations of the non-homogeneous 3D stress state of wedge indentation. Simulated load versus depth and strain field predictions show very good agreement with experimental wedge indentation results. Finally, it is shown that a hyperelastic model calibrated using only a single deformation mode yields poor results for other primary and 3D deformations, and thus multiple primary deformation modes (preferably all three) should be considered.

Square grid deformation in wedge indentation: a new mathematical approach

The square grid deformation approach is generally employed to forming processes solved with the aid of slip-line field in which a ductile body is supposed to be made with arrays of square grids of finite sizes before the deformation process. After the application of the load, as the deformation occurs, square grids are deformed. The square grid deformation has three utilities—(1) visualization of actual deformation process, (2) prediction of trajectory at any point and (3) computation of strain. The theory of square grid deformation mathematics was originally developed by Hill considering the linear formation of the lip. The present work develops a new mathematical approach for deformation of square grids considering a parabolic lip formation when a rigid wedge is gradually indented to a ductile block of semi-infinite size.

Limit analysis and frictional contact: formulation and numerical solution

The evaluation of structural integrity involves the determination of a limit state. If there is plasticity, limit analysis theory takes place. The aim of this paper is to present a limit analysis formulation considering friction at the contact interface. The deduction of this formulation involves the study of contact mechanics, unilateral conditions at normal direction and a slipping rule for the tangential direction. Concerning the contact between a rigid and a deformable body, at limit state there is permanent contact between the bodies and the contact length is supposed known. These hypotheses enable the development of a limit analysis formulation considering friction dissipation. The solution of a limit analysis problem is based on duality between the static, kinematic, mixed and the set of optimum conditions and its relation with the solution of a non-linear programming optimization problem with constraints. The solution is based on Newton method with contraction and relaxation techniques, associated with condensation technique to solve the linear complementarity problem at contact. As an application, the influence of friction coefficient at tool-specimen interface on the wedge indentation is evaluated.

Investigation into the evolution of interface fracture toughness of thermal barrier coatings with thermal exposure treatment by wedge indentation

Abstract