Foam material is one of the ingredients that are frequently used for controlling of touch feeling on the contacting part of various products like bed mattresses. For better sleep, it is necessary to design to control the touch feeling of the mattresses. Touch feeling depends on various properties of the foam material, and the shape characteristics of the contact part also give humans various and complicated feelings. According to previous studies, it was possible to easily quantify the physical properties of foam materials by using indentation test. Furthermore, it is necessary to analyze the change in touch feeling due to the shape of contact part of foams for better mattress design. Therefore, in this report, the purpose is to analyze the contact problem including the material property and the shape property of the foam material. A new softness parameter was created by analyzing the contact problem using FEM analysis. Specifically, it is report a design technology based on multiple parameters of tactile sensation that change depending on the shape of the contact part of the foam material.

Tactile sensation by touching motion is one of the basic functions for human beings to recognize the characteristics and information of objects. It is known that information about touched objects is recognized through deformation of the skin, but it is difficult to physically clarify the mechanism of such sensations. In addition, there are several types of mechanoreceptors related to tactile sensation in human skin, and it is necessary to digitize the sensation in consideration of its response characteristics. The purpose of this study is to propose the product design method that recalls physical properties from mechanical information inside the skin in order to evaluate the relationship between human skin deformation and physical properties of touched objects. Humans can recognize the shape and softness of an object by pressing the skin against the surface of the object. The behavior inside the skin can be discussed by modeling the contact between human skin and rigid sphere and analyzing it mechanically by numerical simulation. Finite element method (FEM) was adopted as the numerical analysis method for this elucidation, and the three-layer laminated solid having the epidermis, dermis, and subcutaneous was developed as the numerical model, and mechanical information inside the skin was discussed.

Digital evaluation of touch-feel in textiles is useful to design fundamental functions of clothing. Here, it is necessary to design textiles for a detailed evaluation of the sensitivity in human’s feelings to consider the life-style creation in various aspects. Then, the objective of this paper is to propose a design method for plain-woven fabrics by touch-feel estimation considering the weaving process with the constitutive relations of yarn. Here, a diagram for control weaving is defined by the diameter of the yarn and displacement quantity of the weaving and the cramping by defining the theoretical thickness. For the effective design to consider various processes, unit-cell of plain-woven structures are fundamentally classified as open set models and closed set models. One of the unit-cell models in the finite element method (FEM) for the plain-woven structure is adopted because the adopted model can consider initial-stress distribution in the weaving process. For touch-feel estimation, an analysis model is constructed by warp, weft, and plungers that cramps the woven structure. A series of diagrams to compress with plungers is shown after constructing a plain-woven structure. As for analyzing the weaving process and the touch-feel estimation in one model, realization of the effective engineering is enabled. This procedure yields that the relationship between the displacement and simulation time suggests for consideration of initial-stress.

Elasticity distributions in structure is one of the typical physical quantities that it is desired to measure nondestructively. Indentation testing is a useful method for the nondestructive measurement methods; however, devices are necessary to evaluate the distribution of elasticity. In this report, a technique to evaluate the elastic distribution in solid is introduced by the information obtained from a simple indentation device. The evaluation is based on Hertzian contact theory that is applied to calculate elasticity from force measured by this indentation device. However, the non-uniform nature of elasticity distribution makes it difficult to apply Hertzian theory. As a solution to this difficulty, a correcting method of elasticity is discussed by analyzing the variation of force information obtained from the device. This correction depends on the method for determining the correction factor decided by the area of elastic range distributed in the solid; this decision is numerically defined by finite element method (FEM). The usefulness of this correction method is confirmed by evaluating the hardness distribution of wood grain. Trees are a representative material with hardness distribution, whose mechanical characteristics depend deeply on wood grain. Therefore, evaluating the ability of elasticity distribution in wood grain has been checked by the correction method discussed in this report. Then, for the problem related to evaluation based on basic Hertzian theory, the expected result can be obtained using wood grain size coefficient and the specification of the probe. However, it is also necessary to examine to the choice of device specifications such as probe dimensions because the elasticity of wood is relatively high and any measured information will have high sensitivity in elastic analyses. Those recommendtion are discussed by showing the devices developed for this evaluation in this report.

Among human sensations, tactile perception has an important role in physics and in living comfortably. It is already known that surface roughness greatly affects the feel of solid objects, but the mechanics of the relationship between feeling and physics, as well as their effects, are difficult to determine. This study, aims to clarify the numerical relationship between elastic tactile perception and surface roughness of a rigid body by designing various products with surfaces comfortable to touch. The finite element method (FEM) has been adopted for this clarification, and a numerical model of human skin with 3 layers, epidermis, dermis, and subcutaneous, has been developed to discuss the mechanical effects of touch movement. This skin model is used to evaluate the distribution of skin deformations during the process of touch movement, and the analysis of the tactile perception is done by discussing the distribution change due to touching objects. The change in distribution of deformation is mainly discussed in terms of pressure under the epidermis, and various patterns of distribution are inspected by changing the diameters and pitch ratio of a uniformly spread ball used as a plain surface. By comparing the relationship between distributions of rigid and elastic surfaces, similar distributions of pressure in the skin model were observed, and the relationships of the distribution are summarized to solve the mechanics of touch feeling. In this summarization, the maximum pressure and the maximum gradient of pressure distribution are adopted as parameters for the analysis. The analysis shows that it is numerically possible to represent the elasticity recalled by the rigid surface from its relationship with the elastic surface when they have the same maximum pressure and maximum inclination of pressure. The importance of maximum inclination of pressure for touch feeling is also shown here.

Unit-cell modelling is one of the useful methods to analyze deformation in periodic structures like honeycombs, perforated boards, and woven fabrics. The initial state of the structures is considered to be stress-free in ordinal deformation analysis, but in actual practice, the analysis is difficult, because initial stresses like assembly stress and residual stress need to be considered, as they are known to affect the results. In this study, a technique of taking into account the initial-stress state in woven fabrics is discussed, which has resulted in the establishment of a precise design method for textiles. LS-DYNA, which is a general-purpose finite element (FE) software, has been utilized to simulate the complex deformations in woven fabrics. In this software, a function of the global constraint on boundary conditions facilitates the analysis of periodic structures, but causes difficulties in computing the initial stress states in woven fabrics, as the conditions of mechanical equilibrium have to be satisfied in the governing equations. In particular, duplicated definitions of forced displacement and periodic deformation make the computation impossible, hence, a phantom-element has been introduced to ease the FE analysis by defining these quantities. A unit-cell of the woven fabric is identified and the initial states in stressed conditions can be estimated for periodic structures of plain-woven fabrics by a periodic-analysis technique of LS-DYNA coupled with the phantom-element, which yields a weaving motion of the yarn in plain-woven fabrics.

Sleeping is one of the most important factors that influence the quality of human life, and this state of existence should be thoroughly investigated to improve the quality of the life. The mechanical design of bedding has great influence on the comfort of a mattress. Thus, objective and conventional techniques to evaluate the mechanics of mattress comfort could help improve the quality of sleep. In this report, an analysis technique for the assessment of the sleeping posture of humans is presented to facilitate the development of mattress design technology. Herein, an analytical model which imitates the human body has been formulated to determine the design parameters of a mass-spring-joint system on a soft underlay. The physical model is composed of five components that represent the head, chest, hip, femur, and calf, with each body part being represented by a simple ball model. The spring joint connecting the five parts reflects the neck, lumbar, hip, and knee joints. The specifications of the body model are determined by actual measurements and previous studies. In order to determine the physical properties of the mattress, two types of mattress urethane foam material are tested using the ball indenter method. The parameters include Young’s modulus, plateau stress, and other physical parameters. Variation due to the type of mattress has been observed in the laying test using a pressure distribution sensor sheet. In the analysis performed using the physical model, the variation in the lying posture and the extent of body sinking are observed to be the same during experiments. Both variations are compared using the change in force distribution in each body part. In conclusion, it was found that the observed changes in distribution are the same in the experimental and physical models. Therefore, the proposed model reliably reflects the design characteristics of the mattress.

Recently, compression wear has become the preferred performance material for many athletes, where it has the effect of reducing the burden on the body by suppressing muscle vibrations and improves athletic performance by providing the body with suitable moderate pressure. This study concerns thigh sleeves formed of compression wear. The optimal level of compression is studied in order to improve athletic performance and reduce muscular strain. Subsequently, the mechanics of the thigh compression sleeve are discussed. Here, the optimal tensile rigidity of the sleeve, which is calculated using the Young’s modulus of the sleeve in the circumferential direction, is discussed with the aim of reducing muscular strain. The finite element method model is adopted to represent the thigh, which commonly experiences muscle strain during running. The model is constructed using a semi-circular shape, which represents the thigh cut in the transverse plane. The model consists of two solid components, which reflect the muscle (outer) and femur (inner), as well as a shell that covers the thigh. The model generates sinusoidal vibrations, which reflect human behavior when running in a uniaxial direction. The maximum shear strain is approximately half of the tensile rigidity of the sleeve. Indeed, the muscle is sufficiently soft that the tensile rigidity of the sleeve is generally smaller when there is little shear strain on the muscle. From these results, it is concluded that the maximum shear strain of the muscle decreases by almost half when covered by the thigh compression sleeve compared to when no thigh compression sleeve is worn. Furthermore, the shear strain of the muscle can be reduced by varying the tensile rigidity of the sleeve when the human is running. Finally, the tensile rigidity of the sleeve can be decreased to reduce the shear strain of the muscle as it softens.

Because the fracture behaviors of soft materials are complex, high-precision technology is needed to perform the detailed analysis necessary to produce more effective materials. Indentation methods exist to characterize the fracture behavior of soft materials, with fractures varying in accordance with the shape of the indenter. Thus, it is important to clarify the relationship between indenter shape and the fracture behaviors of soft materials, and necessary to consider the complicated deformation patterns induced by the mechanical nonlinearity of the materials. To this end, various needle-like indenter shapes are modeled via a finite element method (FEM). In this study, we employ a cone-shaped reference needle. Then, the shape is changed to have the tip form a curvilinear indentation, resembling a steep mountain ridgeline. In addition, shear strain is set as the fracture criterion for soft material in the FE analysis since the shear force resulting from penetration primarily damages the soft materials. Regarding the force applied to the needle, there is a tendency for the force to become smaller as it more resembles a cone shape. There are three fracture types: holing, opening, and slitting. Holing is generated by the cone needle, and the fracture of soft material appears along the shape of the needle. Opening fractures are generated by the needle with a curvilinearly spreading tip, forming a small slit on the surface of the soft material. Lastly, slitting fractures are also generated by the needle with a curvilinearly spreading tip, but the resulting slit is deepened without damaging the tissue surrounding the needling. These fracture types can also be classified according to the fracture area of the soft material surface, with slitting resulting in the smallest fracture area.

Air-rich soft materials are widely used in textile products, such as clothes and towels, because they exhibit good heat-retaining properties. Quantification of the heat-retaining properties of materials is necessary for product design engineering. Here, the behavior of heat transfer in the layer structure of the material is evaluated to formulate its kinetics. Such evaluation can address the barriers to appropriate design. The heat transfer kinetics of the multilayered structure of the materials are evaluated by assessing the surface temperature of the outer layers. The evaluation equation for kinetics is formulated by applying the fundamental relationship of heat transfer, which is represented by thermal conductivity and the heat transfer coefficient. In the experimental evaluation, a simple wind tunnel was developed using a blower, hot plate, and digital radiation temperature sensor. The temperature of the hot plate was set at three levels. In the evaluation of surface temperature, the quantity of infrared ray was measured using the digital radiation temperature sensor, because it could be used without mechanically influencing the specimen. The surface temperature of the materials was measured by changing the number of layers from one to eight. In the evaluation of heat transfer kinetics, some properties of the conductivity and the transfer were identified by the formulated relationship for the kinetics of the layered structure and the numerical technique of inverse analysis. It was found that the heat conductivity of the material and heat conductivities between the layers can be identified by the examination of surface temperature variation caused by the change in the number of layers. Then, the crush effect of air-rich structures can be assessed by compressing the material and then analyzing the behavior change in heat transfer caused by the crush. The difference between the observed results and those obtained without the crush of air-rich structure was significant. Thus, we concluded that the physical properties of heat transfer in a multilayered structure of air-rich soft materials can be identified using the surface temperature change in the material resulting from the number of layers. Therefore, it is important to measure its behavior without the crush of the air-rich structure to evaluate the most natural state of the material appropriately.

Many industries, such as the biotechnology, food, and beauty industries, require noninvasive methods for quantifying material stiffness. One such method is the indentation test, which is particularly useful in evaluating the mechanical characteristics of soft materials. However, it is difficult to identify mechanical characteristics of the distinct layers of layered materials such as human skin due to their physical integration with one another. There is particular interest in evaluating the softness of the stratum corneum (the outermost layer of skin) in the cosmetics industry, where the effect of cosmetics should be restricted to this outermost layer. The purpose of this study was to develop a method to determine the elasticities and thicknesses of discrete layers in a layered material by using an indentation test. This paper discusses the results of this indentation test derived via the finite element method (FEM). Here, the finite element (FE) model is constructed by a layered structure of flat surfaces with given Young’s moduli. The FEM results suggest the existence of a law among the elasticities and layer thicknesses of a layered material.

The incidence rate of breast cancer for women in Japan is increasing each year. The three main methods of screening for breast cancer are finger palpation, mammography and breast ultrasound. These methods must be improved to decrease the incidence rate. This involves the development of personal, easy-to-use devices that facilitate cancer diagnosis. This study evaluates an indentation device developed to imitate traditional finger palpation and identify the position of the tumor inside the breast. The identification procedure is based on the extended Hertzian contact theory, which was developed to evaluate the elasticity of a thin specimen. In this extended theory, the thickness effect of the specimen is represented by a thickness parameter, and the position can be identified by the analysis of the effect. The procedure is verified by using FEM for ideal inclusion model in soft object, and the accurateness of the identification is discussed for the development. In the verification, some difference in the identified position between the condition and the result of FEM is observed with the difference of the identified elasticity of the object. It was reported that the approximation of accurate elasticity could affect the accuracy of position identification. Subsequently, the identification accuracy of Young’s modulus and thickness of specimen is discussed considering the problem of inclusion. Using the proposed approach, high accuracy can be observed in the range of 5 mm to 15 mm; however, a greater level of accuracy in identification remains to be achieved in other ranges. Thus, it is concluded that identification is possible using the extended Hertzian contact theory; however, for accurate identification of cancer position in a breast, the theory requires further modification.

We examined glioma tissues immediately after en-bloc removal during surgery and measured elastic modulus, viscosity, and viscoelasticity of the gray and white matter to confirm the feasibility of measurement using an indentation device. Measurements were obtained from excised parenchymal brain tumor tissue of four adult patients. The white matter exhibited higher elastic modulus than the gray matter in all patients. Viscoelasticity analysis was performed in two patients, with viscoelastic behavior observed in the white but not in the gray matter in both patients. The loss of viscoelasticity in the white matter observed in one patient may be related to the calcification visible in the preoperative computed tomography image.

In order to design the products made from soft materials, it is important to quantify the deformation characteristics of them for the quality and reliability of their design. But the quantification is ordinary difficult because of large deformation due to its softness even if the tensile test which is one of the fundamental technique is easily applied to the quantification for hard materials. Here, usefulness of indentation test is reported for soft materials by extending the Hertzian contact theory. Then the indentation technique based on the contact theory is adopted for quantification in this paper. This theory is commonly used to evaluate elastic materials, but it is found that inelastic behaviors of solid materials like viscosity and fracture can be quantified by the extension of the theory. In this paper, an evaluating equation is formulated and applied to quantify in-elasticity of various materials and it is known that an equation can analyze the variation of soft materials objectively, and the analyzed results has high compatibility to uniaxial test like the fundamental Hertzian contact theory.

Super elastic alloy (SEA) has good flexibility with moderate rigidity and then is widely used in eyeglasses, bras and so on. SEA’s flexibility is based on the phase transformation between austenite and martensite structures of material metallurgy, and it is known that the transformation can be controlled by heating and cooling the material. The active deformation of SEA is already reported as controllable by the heating and cooling under pre-stressed condition, but it is known that the deformation is on / off control because the material has very strong nonlinearity in their stress-strain relationship. Then the development of smooth control of SEA’s active deformation is studied to realize soft actuator in this report. The smoothness of the control is realized by the multiplying the wires of SEA in actuating unit of 1DOF actuator. The theory of SEA controller is formulated by using the constitutive equation of the metallo-thermo-mechanics which represents the kinetics of phase transformation between austenite and martensite structures. The developed controller with the formulation is applied to actuate 1DOF actuator with multiple wires of SEA for the verification of the realization. The qualitatively match between theory and experimental results is observed here but quantitatively mismatch has occurred in this report. In the discussion of this paper, it is shown that the mismatch is occurred because the formulation is based on the ideal condition without the deformation of actuator unit. Then this report shows that it is important to design the soft actuator not only their actuating element but also the other elements which affect the deformation behavior of the actuator as a total unit.

An indentation test can easily measure the deformation characteristics of a material, because it does not require a test specimen to be cut from the material being examined. The applicability of this test is usually restricted to evaluating the fundamental characteristics of deformation, such as elasticity and plasticity; however, it is also useful if the test can be applied for the fracture evaluation of materials. Therefore, in this study, the fracture behavior of materials is discussed by performing indentation tests. The evaluation procedure depends on the variation in the indentation force owing to the differences in the deformation behavior. The observed variation is analyzed via the fractography of the material. A simple formulation is derived from the results for the development of a material evaluation method. Finally, the importance of the choice of the indenter diameter is explained in terms of the accuracy of the plateau stress of the porous material.

Indentation technique for the mechanical evaluation of soft materials like biological tissue is discussed in order to develop the medical device of palpation. Here, the Hertzian contact theory is functionally extended to measure the mechanical characteristics of thin, viscous and fragile tissue, and then it is also modified to evaluate the elasticity and friction of the soft materials. The modification of the contact theory is applied to manufacture a trial device experimentally, and its availability is studied by using the FE analysis with the boundary condition of contact and friction.

Various mechanical effects occur in the human skin when it touches the texture which has micrometric scale. Since these mechanical effects in the skin are complicated, their study is necessary. The purpose of this study is to ascertain these mechanical effects by applying numerical analyses for a detailed discussion. In particular, the analysis confirms the differential effects in the skin due to a periodic variation of the texture. By the modeling situation that the texture touches the skin, a stress in the position of skin sensory organs is examined. As a result of the analysis, von Mises stresses at a shallow position of skin showed characteristic effects in the case of a large texture period. It is inferred that these effects occur with a texture period greater than a certain boundary value. Stress values at deep positions of skin are substantially equal without depending on the pressure position of the skin surface. In other words, skin sensory organs of the deep position have a wide receptive field in the numerical analysis of this paper, and this result matches with results of previous researches.

In this study, two types of indentation tests were used for the observation of deformation behavior of biological soft tissue, because indentation testing is an easy method to manage observation and control of the condition of complex tissue specimens. First, a fundamental indentation test was used to evaluate quasi-static deformation behavior of soft tissue. In the evaluation of the quasi-static behavior, elasticity, damage, and fracture of the tissue were analyzed from the profile of reaction force during the indentation. Ball-impact testing with subsonic indentation velocity was used for the evaluation of dynamic behaviors of soft tissue. In the impact test, the viscoelastic characteristics of specimens were evaluated by analyzing stress response, using extended Hertzian contact theory and wave equations, at the moment when a simple ball bullet shot from an airsoft gun strikes the specimen. In the experimental results of the test, an obvious relationship between quasi-static and impact responses of the specimen were observed subjectively. The results are evaluated to analyze the damage and the fracture of the soft tissue for the objective formulation of tissue mechanics. The plateau behavior of reaction force in relation to stress response was also reviewed, in order to quantify the beginning of tissue fracture.

Spherical indentation testing is studied to evaluate the viscoelasticity of soft materials like human body. Here, the Hertzian contact theory is functionally extended to evaluate indentations for the thin tissues. In the expansions, the technique used for evaluating the thickness of finite specimens is first explained by analyzing the experimental results of indentations. Then, the viscoelasticity of soft materials with finite thickness is theoretically derived by defining an equivalent indentation strain for the analysis of the indentation process. The expansions are examined to evaluate its reliability by applying them to measure the viscoelasticity of some soft materials. Furthermore, this technology is applied to the elasticity investigation of the human body. Especially, the measurement results of viscoelastic characteristics of the body of human body are shown and the availability of developed device is discussed to reveal the deformation mechanics of human body in this report.