Indenter Shape Research Articles

Contact strength and deformation of straining free-standing borophene

We apply nanoindentation using molecular dynamics simulation to investigate the contact strength, deformation behaviour, anisotropic cracking propagation and self-reforming mechanism of a single-layer borophene (SLB). The effects of indenter shape, indenter size, borophene membrane size, boundary conditions, temperature, and loading rate on the indentation force, strain and stress distributions, crack directions, and the self-reform ratio of SLB are considered. Especially a cyclic indentation process on the borophene monolayer is also analysed to evaluate its long-term dynamic reliability. The single/multi loading–unloading processes show that the SLB has a perfect elastic deformation when the indentation depth is below or equal to the critical indentation depth. We found that the crack direction is not influenced when changing spherical indenter diameter from 1 to 4 nm or loading rate from 1 to 15 m/s. However, with a conical indenter, the smallest substrate size, and FTE(y) boundary condition, the cracks develop not only in the armchair direction but also in the zigzag direction. Furthermore, the borophene sheet has a high self-reform ratio of 90% (with v = 15 m/s) after being cracked along the armchair direction. Meanwhile, the cracks in the zigzag direction have no possibility of self-reform. At 100 K, after the tenth cycle indentation, the borophene sheet can still preserve its shape while it is broken at 300 K. In summary, this study further highlights the mechanical, long-term dynamic behaviour and potentially speeds up the promising applications of the SLB.

A study on ballistic performance of origami sandwich panels

Sandwich structures with origami cores have shown great potential for engineering applications. However, few studies have been performed on the ballistic performance of origami sandwich panels, particularly on their plastic deformation and ballistic resistance. In this study, rectangular metallic sandwich panels with aluminium origami cores were manufactured. Quasi-static indentation and ballistic impact tests were conducted to explore their ballistic performance. Three different shapes of indenters were considered: flat-ended, hemispherical-nosed and conical-nosed. Plastic deformation and energy absorption capacities were observed and analysed. Subsequently, finite element (FE) simulations using Ansys/Ls-dyna were executed to compare the ballistic performance of sandwich panels with origami cores and honeycomb cores. Parametric studies were also conducted to examine the effect of wall thickness, cell edge length and cell number of origami cores on the ballistic performance of origami sandwich panels.

Improvement of method for estimation of parameters of contact interaction of billet with roll tool in lines of continuous electric pipe-welded mills

A technique for calculating the parameters of the shape of the boundary and areas of contact indentations of a pipe billet with a roller tool of a forming mill, in which the boundaries of the shape of the contact indentation are described by rectilinear lines, and the shape is modeled by triangles on the plane of the pipe billet, is investigated. The results of an experiment on fixing the contact sections of a tubular billet with initial dimensions of 160×1.5×1800 mm from steel 09G2S with rolls in the section of open pass are presented. As a result of the experiment, the contact areas of the pipe billet with the lower and upper rolls were fixed. The boundary of the experimental contact areas are curved arcs. Comparison of the experimental data with the technique showed that the parameters of the boundaries of the contact area according to the technique lead to an overestimation of the values by 30-40 % compared to the experimental data. On the basis of experimental data, the development of the existing technique for determining contact areas is presented, in which the boundaries are defined in the form of arcuate curves. The boundaries of the entry contact sections for the lower and upper rolls are determined by the equations of exponential approximation. Taking into account the equations of the boundaries of the sections, a method is presented for determining the areas of contact sections of a pipe billet on the surfaces of the lower and upper rolls, the results of which do not exceed 6 % of the experimental data. The engineering mathematical software PTC Mathcad Prime 6.0 was used to calculate and construct the areas of contact areas.

Development of Condition Monitoring System for Electric Resistance Spot Welding Used to Manufacture Railway Car Bodies

Stainless steel railway car bodies are assembled by joining the outer plates and the pillar materials using resistance spot welding. In recent years, more and more car bodies are being assembled using laser welding in addition to the resistance spot welding. For this laser welding system, we developed a condition monitoring system considering the processes before and after laser welding as a single system, and obtained and put into practical use an appropriate condition that suppresses spatter generation during laser welding. On the other hand, in resistance spot welding, the current, weld time, electrode load, and electrode tip shape are the main factors that determine the welding quality. Therefore, the configuration of the equipment is less complicated than that of laser welding system, and the condition monitoring is easier than that of the laser welding. In this study, by transferring the concept of the condition monitoring system developed for laser welding to resistance spot welding, we achieved a reduction of more than 60% in terms of electricity consumption and improved the appearance of the car body by optimizing the indentation shape. In addition to this technical achievement, we also present in this paper a case study showing the opportunity for innovation by restructuring the technological paradigm of the resistance spot welding in the production of stainless steel car body shells.

Abrasive Sensitivity of Martensitic and a Multi-Phase Steels under Different Abrasive Conditions.

The wear behaviour of two martensitic and one multiphase steel targeted for abrasion and erosion applications in agriculture and mining industry were investigated in three abrasive test systems with different complexity. Scratch tests were performed with different indenter radii, shapes, and loads. The material behaviour was also investigated in multi-asperity contact systems. Pin-on-disc tests were performed with various loads and abrasive particles, as well as abrasive slurry-pot tests with different sliding velocities, distances, and impact angles of the abrasive media were performed. Comparing the test systems, the tested materials ranked similarly based on their wear performance, however, in each configuration, the dominant variable of the wear mechanism differed. The significance and contributions of test paramecenterters, the material’s mechanical properties (H, , , E, , , W, , ) and the dimensionless numbers formed from them were investigated on the wear behaviour and the surface deformation. Correlation between parameters was established by multiple linear regression models. The sensitivity of the tested materials to abrasion was evaluated taking into account the wide range of influencing parameters.

Mechanical properties evaluation for engineering materials utilizing instrumented indentation: Finite element modelling approach

Instrumented indentation technique gives the possibility to determine the mechanical properties for small specimens and material in service. Several researchers have attempted to evaluate this approach experimentally and investigated the factors that affect it by using different indenter’s geometries for different engineering materials. In this work, the instrumented indentation technique was used to evaluate the mechanical properties experimentally and numerically using finite element simulation to understand the contact mechanics between the indenter surface and the substrate for two types of steel alloys namely ASTM516-G70 and AISI1010 steel. Two shapes of indenters, blunt (spherical) and sharp (Vickers) were used. The results were then compared with the experimental results extracted from the instrumented indentation test. The results have demonstrated a good agreement between the experimental and the finite element simulation results with error bound a ±5 % for young’s modulus and ±7.7 % for yield strength. Whereas excellent agreement is observed in the elastic region and the beginning of the plastic region for the true stress-strain curve. Finally, it is to be emphasized that the obtained results are more applicable for the tested materials and further research is recommended to accommodate other materials as well and to confirm the generality of this method.

Indentation and bifurcation of inflated membranes

We study pneumatically inflated membranes indented by rigid indenters of different sizes and shapes. When the volume of the inflated membrane is beyond a critical value, a symmetric deformation mode becomes unstable and the system follows a path of asymmetric deformation. This bifurcation is analysed analytically for a two-dimensional membrane with either a line or plane indenter for which the stable deformation path is determined by computing the total system potential energy of different configurations. An axisymmetric membrane with indenters of different shapes and sizes is further investigated numerically. In this case, a cylindrical indenter can always trigger bifurcation while a small spherical indenter tends to be encapsulated rather than induce an asymmetric deformation mode. This result suggests that the observed bifurcation behaviour can be actively tuned and even triggered selectively by tuning indenter shape and size. We also demonstrate the effects of friction and biased bifurcation analytically through the example of a two-dimensional membrane with a line indenter.

Chemical constituents and phytochemical properties of floral maize pollen.

Currently, bee-gathered pollen (bee pollen) is commonly used worldwide as a dietary supplement and is recognized for its curative properties. Floral pollen is also important but is less recognized due to a lack of investigation. This study aims to determine the morphological characteristics and nutritional and phytochemical properties of floral maize pollen. Fresh pollen grains harvested from a farm of maize plants are yellow in colour and spheroid in shape. They change to amber and indented prismatic solid shapes when dehydrated. The main composition of floral maize pollen is carbohydrates (44.30±3.73%), followed by moisture (23.38±5.73%), crude proteins (17.16±3.13%), crude fibres (9.56±0.92%), and ash (4.98±0.11%), while the lowest content is observed for crude fats (0.62±0.06%). The predominant mineral is potassium (768.50±11.40 mg 100 g-1), followed by sodium (695.10±9.70 mg 100 g-1), calcium (147.20±12.60 mg 100 g-1), and magnesium (97.30±2.9 mg 100 g-1). The microelements (with average values) consist of iron (49.50±3.30 mg 100 g-1) and zinc (30.00±3.70 mg 100 g-1). Excellent phytochemical properties add value to floral maize pollen. Maize pollen contains a high total phenolic content (TPC) and total flavonoid content (TFC) of 783.02 mg GAE 100 g-1 and 1706.83 mg QE 100 g-1, respectively, and possesses strong antioxidant activity of 10.54 mg mL-1. Maize floral pollen and derived products can serve as future food resources for human consumption and as a source of functional and bioactive compounds in nutraceutical and pharmaceutical industries.

Communication—Impact Behaviors of Pouch and Prismatic Battery Modules

The responses of pouch and prismatic battery modules when they are impacted by two types of indenters from three different directions are investigated experimentally. The test results show that the failure mechanism, peak force and penetration that leads to short-circuit in modules strongly depend on the impact direction, indenter shape, cell form factor and module design. It sheds lights on the abuse tolerance of batteries in different scenarios and demonstrates that the cell type, orientation and module structure should be considered simultaneously in order to improve the battery safety in electrical vehicles.

Investigation on the indentation mechanical performance of aluminum honeycombs

Quasi-static indentation tests were conducted to characterize the mechanical behavior of honeycombs. The local failure mechanisms of honeycombs with different relative density were discussed in detail. Results showed that the spread area of tearing deformations increases with increasing relative density and that difference in the neatness of tearing edges are obvious under different indenter shapes and sizes. The effects of indenter geometry on the plateau force and energy absorption of the honeycombs were analyzed. The tear energy of the specimens was determined, and an empirical formula was proposed to describe the relationship of energy absorption with indenter geometry.

Poroelastic shape relaxation of hydrogel particles.

Hydrogels are commonly used in research and energy, manufacturing, agriculture, and biomedical applications. These uses typically require hydrogel mechanics and internal water transport, described by the poroelastic diffusion coefficient, to be characterized. Sophisticated indentation-based approaches are typically used for this purpose, but they require expensive instrumentation and are often limited to planar samples. Here, we present Shape Relaxation (SHARE), an alternative way to assess the poroelastic diffusion coefficient of hydrogel particles that is cost-effective, straightforward, and versatile. This approach relies on first indenting a hydrogel particle via swelling within a granular packing, and then monitoring how the indented shape of the hydrogel relaxes after it is removed from the packing. We validate this approach using experiments in packings with varying grain sizes and confining stresses; these yield measurements of the poroelastic diffusion coefficient of polyacrylamide hydrogels that are in good agreement with those previously obtained using indentation approaches. We therefore anticipate that the SHARE approach will find broad use in a range of applications of hydrogels and other swellable soft materials.

Effect of plasticity on the experimental characterization of the creep property of a cement paste: Spherical vs. conical microindentation

Microindentation is today a powerful tool for rapidly characterizing the elastic modulus and the logarithmic basic creep of a cement paste. However, a theoretical work proved that a microindentation test with a sharp indenter shape involves stress concentration and delayed plasticity which can cause an overestimation of the estimated creep property. This work aims at experimentally investigating the effect of the shape indenter on the identification of the visco-elastic property of a cement paste by microindentation.First, several microindentation grids were carried out on a cement paste with both a Berkovich indenter and a spherical indenter at different penetration depths or load levels for load control (creep) tests or displacement control (relaxation) tests, respectively. As for a visco-elastic material the duality principle between creep and relaxation holds, a numerical method was developed for predicting the relaxation response from the assumed logarithmic creep compliance. The present results show that only spherical microindentation satisfy the duality principle for which creep and relaxation response can be predicted by a unique logarithmic creep compliance function. Finally, spherical microindentation creep tests at low load as well as spherical microindentation relaxation tests provide a greater indentation modulus M and contact creep modulus Cv as likely less affected by possible plasticity effects.

Orientation Dependence of Plastic Deformation Behavior and Fracture Energy Absorption Mechanism around Vickers Indentation of Textured Ti<sub>3</sub>SiC<sub>2</sub> Sintered Body

In order to clarify plastic deformation behavior and mechanism of fracture energy absorption of Ti3SiC2, Vickers indentation tests were conducted for Ti3SiC2 sintered bodies with various textured orientations. Textured Ti3SiC2 sintered bodies were fabricated by slip casting in a strong magnetic field and spark plasma sintering (SPS), and their orientation distribution were analyzed by SEM/EBSD. It was found that for the textured Ti3SiC2, the plastic deformation behavior around Vickers indents such as an indent shape and a grain pile-up were strongly affected by basal slip and kink deformation. Furthermore, the fracture energy absorption mechanism around the indents also depended on the texture orientations. From our results, it is concluded that the most effective factor for suppressing the crack propagation was the grain pile-up, and the second one was crack deflections.

Parametric Study on the Safety Behavior of Mechanically Induced Short Circuit for Lithium-Ion Pouch Batteries

Abstract Safety issues of lithium-ion batteries under mechanical abuse have attracted worldwide attention due to its high uncertainty and high risks, following by the rapid increase of market share for lithium-ion battery-driven smart products. In this work, the safety behavior of a pouch battery under mechanical abuse conditions is numerically investigated using a simultaneously coupled mechanical–electrochemical–thermal model. The short-circuit and electrochemical–thermal responses of lithium-ion batteries under various mechanical abuse conditions are successfully predicted and compared. The main impact factors, including the state of charge (SOC), indenter shape and size, and loading displacement, are systematically studied and analyzed. The comprehensive parametric studies show that the battery is in a more dangerous state under higher SOC, identify the critical distinction of the short-circuit behavior between sharp indenter and blunt indenters for battery, and explain the discrepancies in the repeated mechanical abuse tests. These conclusions provide theoretical insights for understanding the failure mechanism of lithium-ion batteries under mechanical abuse, and technical support for the safety design of battery packs.

The Interrelated Mechanics of Poroelastic Gels in Time- and Frequency-Domain Detected by Indentation

The force response of poroelastic materials including poroelastic gels to indentation is known to be time- and space-dependent (i.e., a function of indenter shape and size). Despite the complexity of the poroelastic response and in contrast to viscoelastic mechanics, poroelastic mechanics can be captured in terms of several intrinsic mechanical properties, such as elasticity, permeability, and Poisson ratio. While these intrinsic properties can be found from time-domain or frequency-domain master curves, indentation is usually conducted and analyzed only in the time domain using stress-relaxation or creep experiments. This paper advocates using frequency-domain analysis of poroelastic gels by reviewing and analyzing the relevant works of the literature. The analysis and methods, proposed here, enable researchers to characterize dynamic moduli of poroelastic gels in frequency domain using only a few experimental defining parameters. The authors have intentionally provided extensive details and background, to make this work useful for researchers who consider using frequency-domain analysis for the first time. This work reviews and explains the instantaneous elastic modulus, depicted over normalized time as a unifying and understandable set of master curves for time-domain stress relaxation tests on poroelastic gels for cylindrical, conical, and spherical indenters. The dynamic elastic modulus, depicted over normalized frequency, are derived symbolically and numerically and explained for the first time as master curves with simple transfer function in the frequency domain for presenting poroelastic mechanics of gels.

Experimental and numerical study on the penetration of stiffened aluminium alloy plates punched by a hemi-cylindrical indenter

ABSTRACT The present paper continues the recent works reported by Liu et al. (2020) where quasi-static indentation experiments and finite element simulations were reported to investigate the plastic behaviour and failure of four stiffened aluminium-alloy plates punched by a rigid hemispherical indenter: one bare plate, one butt-welded plate, two plates with respectively one and two flat-bar stiffeners. Here specimens with the same geometry are investigated using a rigid hemi-cylindrical indenter to examine the effect of the indenter shape on the deformation and collapse modes. The experimental comparison shows the different structural deformation and failure mechanisms of welded aluminium alloy panels. The finite element analysis discusses the importance of the modelling of welded joining details, the boundary conditions and the material degradation at welded heat-affected zones and at the same time illustrates the similarities and differences between impact analyses of aluminium and steel stiffened plates.

PENETRATION RESISTANCE OF RUBBER VULCANIZATES

ABSTRACTAspects of penetration resistance of rubber compounds have been studied by developing a quasi-static test. The effects of indenter material and design, nature and dosage of fillers, and crosslinking density were investigated. Indenter material was found to have a negligible contribution to the penetration characteristics of the rubber compounds, whereas the conical indenter's shape and size of the tip were important. A change in the slope of the generalized penetration characteristic curve of the developed quasi-static test was considered to be the fracture initiation point. Although fracture initiation was early at higher carbon black loading, the overall penetration resistance was improved due to hysteresis, which was in accord with the impact energy method. This was a unique observation. The carbon black–filled sample was compared with the silica-filled vulcanizate. Surface morphology of the specimens penetrated at different energy levels was examined using scanning electron microscopy. A theoretical interpretation of the forces acting at the tip of the indenter and the energy requirement while penetrating a rubber compound against a conical indenter has been proposed. The initiation energy for penetration has inverse square root dependence on the Young's modulus of the compounds. The energy required for crack propagation in contrast, was directly proportional to the Young's modulus and also correlated with the hysteresis loss and frictional coefficient for the carbon black–filled vulcanizates.

Transmission loss of plates with multiple embedded acoustic black holes using statistical modal energy distribution analysis

Acoustic black holes (ABHs) in beams and plates have been extensively studied as a passive method for vibration attenuation and noise reduction. However, most research to date has focused on analyzing the behavior of a single ABH structural element, using numerical or semi-analytical deterministic approaches. If ABHs are to be exploited for practical industrial applications, there is a need to characterize their performance in complex built-up structures and to describe them with statistical methods in the mid-high frequency range. This paper presents a first step towards this goal by employing statistical modal energy distribution analysis (SmEdA) to evaluate the transmission loss of ABH panels separating two air cavities. SmEdA splits vibroacoustic systems into subsystems and establishes power balance equations between the modes belonging to different subsystems. This avoids the energy equipartition assumption of traditional statistical energy analysis (SEA) and extends it to low modal overlap systems. In this work, the benefits of embedding ABHs on plates for noise reduction between cavities are predicted with SmEdA. The role played by the size, shape and number of ABH indentations on the plate are inspected, as well as the influence of other parameters like the truncation thickness, ABH order and damping. The effects of added mass and stiffness of the damping layer are investigated and it is observed that, with proper design, ABH plates can exhibit substantial transmission loss improvement in the vicinity of the critical frequency of uniform plates. Both resonant and non-resonant transmission are considered in the analysis.

Static Residual Tensile Strength Response of GFRP Composite Laminates Subjected to Low-Velocity Impact

The dependency of the static residual tensile strength for the Glass Fiber-Reinforced Plastic (GFRP) laminates after impact on the impact energy level and indent shape is investigated. In this study, two different laminates, unidirectional, [0°2]s) and TRI (tri-axial, (±45°/0°)2]s), were prepared using the vacuum infusion method, and an impact indent on the respective laminates was created at different energy levels with pyramidal and hemispherical impactors. Impact damage patterns, such as matrix cracking, delamination, debonding and fiber breakage, could be observed on the GFRP laminates by a scanning electron microscope (SEM), and it is found that those were dependent on the impactor head shape and laminate structure. Residual in-plane tensile strength of the impacted laminates was measured and the reduction of the strength is found to be dependent upon the impact damage patterns. Furthermore, in this study, stress concentrations in the vicinity of the indents were determined from full-field stress distribution obtained by three-dimensional Digital Image Correlation (3D DIC) measurement. It was found that the stress concentration was associated with the reduction of the residual strength for the GFRP laminates.

Automated Vickers hardness measurement using convolutional neural networks

A method based on convolutional neural networks (CNN) was proposed for robust automated measurement of Vickers hardness. Vickers hardness testing is generally applied to metals but can be conducted on other materials such as ceramics. Typical image processing methods tend to fail to detect the indentations in materials with rough surfaces, noisy patterned surfaces, distorted indentation shapes, or cracks. Automated measurement methods must be robust and versatile to process materials with these anomalies. A CNN method was chosen to detect the bounding box of the Vickers indentation, as the technique automatically extracts features required to recognize the region of an object. The diagonal lengths and Vickers hardness values calculated using the CNN method were similar to the reference manual measurements, even in samples with rough surfaces, noisy patterned surfaces, distorted indentation shapes, or cracks. The CNN method is a promising automated alternative for robust and versatile prediction of Vickers hardness.