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The indentation behaviour of sandwich panels is significant to incipient damage and is known to be affected by a number of dominant parameters. However, it is challenging not only to demonstrate how those few dominant parameters influence the indentation behaviour but also to ascertain that such influence was coupled to the variation of the other dominant parameters. The paper aims to discuss these issues.

In this work, the authors adopted a controllable quasi-static testing to carry out a diagnostic interrogation on the nature of incipient damage in laminate-skinned sandwich panels using hemispherical indenter and used photographs taken from the cross-sections of all the cut-up tested specimens, which were stopped both just before and after the initial critical loads, respectively, to confirm the mechanism of the incipient damage. Sandwich panels with aluminium honeycomb core had carbon/epoxy skins of two different thicknesses and lay-ups and hemispherical nosed indenter had three different diameters.

The authors found that: the incipient damage mechanism in all the panels was combined delamination in the skin and core crushing without debonding; doubling the skin thickness had the significant enhancement on critical load and indentation and this enhancement became greater for the larger indenter diameters; the indenter diameter had the moderate effect on critical load in the thick panels from 8 to 14 mm but had the negligible effect on thin panels and no effect on the thick panels from 14 to 20 mm; varying the skin lay-up or support had little effect on the indentation behaviour.

These findings were limited to the constant core density and core thickness. Varying the former significantly could alter the findings accordingly.

The results of this work should be tremendously useful to design and analysis in industrial applications of sandwich structures in aircraft, vehicles, marine vessels and transport carriages for situations involving localised loading and deformation.

The results of this research work is one of the very few that demonstrated a systematic understanding of the indentation behaviour characteristics of sandwich construction, which is vital to the establishment of indentation law for sandwich structures in future.

This paper gives a bibliographical review of the finite element modelling and simulation of indentation testing from the theoretical as well as practical points of view. The bibliography lists references to papers, conference proceedings and theses/dissertations that were published between 1990 and 2002. At the end of this paper, 509 references are listed dealing with subjects such as, fundamental relations and modelling in indentation testing, identification of mechanical properties for specific materials, fracture mechanics problems in indentation, scaling relationship for indentation, indenter geometry and indentation testing.

This paper presents an experimental study of the influence of variables such as strain rate, the number of fabric plies, the type of fabric, the kinds of fibre and the shape of indenter on the indentation of fabric under differently shaped pinch gripper.

This experimental study will be approached from three different angles. It will look into an indenter pressing a sample with a much larger size, which is important in practice in the world of grasping by a pinch gripper. It will research a flat indenter, but also an indenter with a curved surface and will investigate fabric compression particularly with regard to the differences between single‐layer and multi‐layer stacks.

The type of fabric architecture and the kind of fibre have been proven to be important for the indentation. Even more important is the indenter geometry. Evidence collected to date suggests that the grasping action is more sensitive to indenter geometry. This leads to three possible approaches: close regulation of the materials and processes, handling processes to change in the material properties, and thirdly, intelligent systems which can learn from and adapt to each situation.

This study suggests that a picking up operation should change in the material properties, that is, the operation should be controlled by using fabric characteristics as the control information in an intelligent environment.

Previous work on compression has been concentrated on an indenter with a size identical to a specimen, this study will look into an indenter pressing a sample with a much larger size. On compression, previous work has focused on single‐layer fabric compression by a flat indenter, but this research will not only research a flat indenter and single layers, but also an indenter with a curved surface, and multi‐layer stacks.

Indentation tests performed in creep damage materials show that slopes of initial portions of unloading curves which are often used to calculate indented modulus can characterize creep damage. To evaluate the influence of different indenters in determining creep damage, conical, spherical and cylindrical indenters which are all self‐similar in shape were considered by using the Finite Element Method (FEM). Indentation load (P)‐displacement (h) curves and equivalent elastic modulus ( E * )‐creep damage (ω) curves were given. Results show that the cylindrical indenter is appropriate for “soft” materials, the conical indenter is suitable for small creep damage materials, and the spherical indenter can be used in many other materials.

Tactile sensation is an important sensory function for robots in contact with the external environment. To better acquire tactile information about objects, this paper aims to propose a three-layer structure of the interdigital flexible tactile sensor.

The sensor consists of a bottom electrode layer, a middle pressure-sensitive layer and a top indenter layer. First, the pressure sensitive material, structure design, fabrication process and circuit design of the sensor are introduced. Then, the calibration and performance test of the designed sensor is carried out. Four functions are used to fit and calibrate the relationship between the output voltage of the sensor and the contact force. Finally, the contact force sensing test of different weight objects and the flexible test of the sensor are carried out.

The performance test results show that the sensitivity of the sensor is 0.93 V/N when it is loaded with 0–3 N and 0.23 V/N when it is loaded with 3–5 N. It shows good repeatability, and the cross-interference between the sensing units is generally low. The contact force sensing test results of different weight objects show that the proposed sensor performs well in contact force. Each part of the sensor is a flexible material, allowing the sensor to achieve bending deformation, so that the sensor can better perceive the contact signs of the grasped object.

The sensor can paste the surface of the paper robot’s gripper to measure the contact force of the grasping object and estimate the contour of the object.

In this paper, a three-layer interdigital flexible tactile sensor is proposed, and the structural parameters of the interdigital electrode are designed to improve the sensitivity and response speed of the sensor. The indenter with three shapes of the prism, square cylinder and hemisphere is preliminarily designed and the prism indenter with better conduction force is selected through finite element analysis, which can concentrate the external force in the sensing area to improve the sensitivity. The sensor designed in this paper can realize the measurement of contact force, which provides a certain reference for the field of robot tactile.

The purpose of this paper is to investigate the use of nanoindentation with a Berkovich indenter as a method of extracting equivalent stress‐strain curves for the base metal and the welded zone of a friction stir welded aluminum alloy.

Friction stir welding is a solid‐state joining process, which emerged as an alternative technique to be used in high strength alloys that were difficult to join with conventional joining techniques. This technique has a significant effect on the local microstructure and residual stresses combined with deformation. Nano‐ and micro‐indentation are the most commonly used techniques to obtain local mechanical properties of engineering materials. In order to test the reliability of nanoindentation technique and to connect nanoscale with macroscale, the indentation hardness‐depth relation established by Nix and Gao was applied on the experimental values.

The predictions of this model were found to be in good agreement with classical hardness measurements on AA 6082‐T6 aluminum alloy. Also, finite element method provides a numerical tool to calculate complex nanoindentation problems and in correlation with gradients theories forms a well‐seried tool in order to take into account size effects.

By studying this alloy, the paper reviews fundamental principles such as stress‐strain distribution, size effects rise during nanoindentation and the applicability of finite element method, in order to take into account these issues.

Lightweight alloys are of major concern, due to their applicability, in transport and industry applications. The purpose of this paper is to perform a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique, through investigation of creep behavior. Additionally, possible explanations on the time dependent behavior and the influence of the hold period at maximum load and the loading rate on the elastic modulus and hardness results are also analyzed and discussed.

In this work, a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique was performed, by varying the loading rate, the maximum applied load and the loading time. The stress exponent values are derived from the displacement‐holding time curves. The present experimental setup includes three different approaches: variation of loading rate, maximum applied load and loading time. The creep deformation mechanisms of the alloy, which are dependent on experiment setup, are discussed and the characteristic “elbow” behavior in the unloading part of the curves is also reported.

The authors found that the stress exponent values obtained are dependent on the applied peak loads and indentation loading rates. Nanoindentation creep testing of aluminum AA6082‐T6 revealed significant creep displacements, where the strain rate reached a steady state after a certain time and the stress decreased with time as the displacement increased during the creep process. The slopes of strain rate versus stress curves (exponent of power‐law creep) for different maximum loads and various holding times, were investigated.

The stress exponent of the constant‐load indentation creep, in all three types of experiments, was found to reduce at low load region. In case of different holding load and time, the stress exponent increased almost linearly and increased very rapidly as the indent size increased, exhibiting an intense size effect.

This study seeks to clarify the behavior of ground materials and the grinding mechanism corresponding to the wear of abrasives, in the grinding process by coated abrasives.

Cemented carbide ball indenters for abrasive grains were used. Cemented carbide ball indenters have a definite shape. Grinding process is carried out using a wear‐testing machine with a reciprocating motion. This is an abrasive wear test. The deformation of the ground material is observed by the measurement of the worn groove and optical microscopic photograph of the worn ground surfaces.

Grinding process regularly proceeds when indenter diameter is small, that is, abrasive has a good cutting quality. However, when abrasives are gradually worn and the cutting quality becomes worse, a groove formed by grinding process is again filled up by the re‐adhesion of the generated worn debris. So, the grinding process by coated abrasives is impossible.

To clarify the effects of indenter shape and its material on the abrasive wear of the workpiece or grinding process by coated abrasives, the additional experiments are now planned using other indenters having different shape or material in the laboratory.

In this research, interesting phenomena in grinding process by coated abrasives are found. This result is useful for the improvement of coated abrasives.

It is clarified that the grinding process by coated abrasives (that is, the behavior of ground material) can be simulated by this abrasive wear experiment.

The purpose of the paper is to present a novel cross-modal sensor whose tactile is computed by the visual information. The proposed sensor can measure the forces of robotic grasping.

The proposed cross-modal tactile sensor consists of a transparent elastomer with markers, a camera, an LED circuit board and supporting structures. The model and performance of the elastomer are analyzed. Then marker recognition method is proposed to determine the movements of the marker on the surface, and the force calculation algorithm is presented to compute the three-dimension force.

Experimental results demonstrate that the proposed tactile sensor can accurately measure robotic grasping forces.

The proposed cross-modal tactile sensor determines the robotic grasping forces by the images of markers. It can give more information of the force than traditional tactile sensors. Meanwhile, the proposed algorithms for forces calculation determine the superior results.

Diamond‐like carbon coatings (DLC) combine high wear resistance with low friction coefficients. Both properties enable the protective layers to sustain wide ranges of loading and environmental conditions. At present, low friction coatings are commonly used on an empirical basis but not as a design element. The reason for the empirical approach is the lack of tools for a description of the interaction between the coatings and the substrate. Furthermore it is difficult to obtain information on the fracture properties of the coating substrate system (e.g. fracture toughness, adhesion, residual stresses). A spherical indentation provides a simple technique to measure quantitatively the fracture toughness and the adhesion of brittle coatings on a ductile substrate with standard laboratory equipment. DLC coatings on a 100 Cr 6 steel substrate are indented by silicon nitride balls with different diameters and different loads. Fracture patterns (circular and radial cracks, delamination) are analyzed by finite element calculation and the fracture toughness of the coating itself along with the interface toughness are estimated.