It is extremely important that the structures that support our lives have the necessary forces to withstand external forces and loads during the period of use. However, we cannot see the force information and whether the mechanical behavior has deteriorated or not. Instead, we predict the strength of the structure based on our experience and knowledge, and feedback to the design. However, some questions shod be remaining. Are the past knowledge and simulation correct? Are there any assumptions? Is there any information that we are not aware of? In response to this issue, we have been visualizing "force information" originating from structural materials and structures by utilizing our originally developed "mechanoluminescence (ML) technology" that can visualize dynamic strain distribution. This section introduces mechanoluminescence technology and its visualization strategy, as well as health monitoring, improvement of design and prediction, and development of standards for the use of visualized information.

  Polymeric materials are widely used because of the lightness and flexibility, which other materials do not have. Recently, the strength has been also improved, resulting in the use as structural materials in transportation machines. The use and demand will continue to increase toward the realization of a sustainable society. However, the failure, fatigue, and deterioration mechanisms are poorly understood because polymer has a history of only 100 years since the concept was proposed. Monitoring and elucidation of the mechanisms are pressing issues to improve the durability, safety, and reliability. Therefore, visualization of force and damage generated in polymeric materials has been studied around the world. In this review, we overview previous research on the visualization using functional dyes, which change the color and/or luminescence properties in response to force. This approach enables to visualize the force and damage at the molecular level without sacrificing the material properties, promising detailed evaluation and understanding of the mechanisms.

For understanding the stroke mechanisms relating to hemodynamics, it is necessary to study the stress interaction between the wall of the vessel and the flowing blood. However, it is very challenging to perform CFD for fluid-structure interactions with complex structural deformations, thus there is a high demand for the experimental visualization of the unsteady stress field in the medical field. In this study, we developed a high-speed photoelasticity of polymer gels and liquid polymers for understanding stress interaction between blood vessels and blood. This method using a high-speed polarization camera measures the polarization state (birefringence in proportion to stress) of polymer gel and liquid polymer. We confirmed that the phase retardation, which is the spatially integrated value of birefringence, is correlated with the principal stress difference. Besides, we also attempted the measurement of the retardation field of polymer gels and liquid polymers under pulsating flow conditions.

  This paper presents a method for visualizing the distribution of residual thermal strain for underfill (UF) materials using the sampling moiré method to evaluate the internal thermal deformation of semiconductor components. In this method, microgrids are formed in advance on the sample surface at room temperature, and the residual thermal strain distribution can be measured at any temperature relative to the sample formation temperature. A heating chamber for flip chip package (FCPKG) was designed under a laser microscope, and the developed method was used to measure and compare the residual thermal strain distribution at 150℃ in FCPKG of two types of UF with different glass transition temperature (Tg) Experimental results of residual thermal strain distribution are reported.

  Visualization of zero-group-velocity (ZGV) Lamb waves was done by a photoelasticity technique for understating its vibration behavior associated with bond quality of a polymer adhesive joint. ZGV Lamb wave which cannot propagate but their phase velocity show finite possesses a large potential for assessing bonding quality in an adhesive joint. However, an effect of the bond quality on vibration behavior of the ZGV Lamb wave is still unclear. Photoelasticity technique enable us to understand vibration behavior in Lamb waves intuitively without any boundary conditions in advance. Photoelastic images of ZGV Lamb waves for the glass plates in a lap-joint with well and weak quality were obtained. In the well bonded sample, the identical vibration mode was observed in both glass plates as adherents. On the other hand, in the weak-bonded sample, different vibration modes in the two adherents appeared.

  The basic principle of the 2D displacement/strain measurement using global DIC and a method for obtaining stresses from the measured strains are described. In this method, a finite element mesh is defined so that it overlaps the measurement target in the image, and all nodal displacements of the mesh can be determined simultaneously by using the correlation of gray value distributions. After determining the nodal displacements, the strains in the elements are computed using the displacement-strain relationship. If the strain is small, the strains can be obtained from the displacement gradient. If the strain is not considered small, the strains are obtained from the deformation gradients based on finite deformation theory. After calculating the strain, if the material properties and constitutive equation of the object to be measured are known, the stress distribution can be obtained. As examples of stress visualization, stress concentration around a circular hole and stress distribution near a crack tip are shown. The evaluation of fracture mechanics parameters for the crack example is also presented.