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We present a domain decomposition technique combining the finite-element analysis and a multiscale simulation scheme that is termed the seamless-domain method. This technique is applicable to any type of linear problems and has the below different features from conventional substructuring techniques used for finite-element methods such as the super-elements. Adjacent substructures do not need to have the same finite-element mesh or the same node layout at their interface. Therefore, the proposed technique allows us to connect a substructure having a coarse mesh and another substructure having a fine mesh. Additionally, the neighboring substructures are partially overlapped each other around their interfacial region. The overlapped region attempts to generate continuous dependent-variable distribution(s) at the interfacial region. We present four types of numerical experiments related to linear elasticity to investigate practical feasibility of the proposed technique and evaluate an effect of different finite-element meshes in region shared by two substructures on the computational accuracy.

Carbon fiber reinforced polymers (CFRPs) have high specific strength and many other advantages in mechanical properties compared with conventional metal materials. However, a small out-of-plane impact load can easily cause serious damage in a CFRP laminate because of its laminated structure composed of anisotropic layers. Although ultrasonic inspection is generally performed to detect the damage and estimate its location and size, the method usually requires both long inspection time and a large cost. Thus, a low-cost and in-situ system for monitoring collisions of foreign matters is required to identify the area where the ultrasonic inspection must be conducted. When a foreign matter, which is regarded as a charged body because any object is charged to a greater or lesser extent, approaches and hits grounded electric conductive materials such as a CFRP laminate, an electric current caused by electrostatic induction flows into the ground. We analyzed the electric current and conducted a falling-weight impact test to elucidate the mechanism of generation of the electric current. In addition, we proposed a collision monitoring system which utilizes the characteristic waveform of the electric current and the electrical anisotropy of a CFRP laminate, and conducted a falling-weight impact test to verify the validity of the proposed method. As a result, we succeeded in localizing the collision of the charged body in sufficiently high spatial resolution using the proposed system.

In this paper, we applied a multiscale numerical scheme called the seamless-domain method (SDM) to nonlinear elliptic boundary value problems. Although the SDM is meshfree, it can obtain a high-resolution solution whose dependent-variable gradient(s) is sufficiently smooth and continuous. The SDM models with only coarse-grained points can produce accurate solutions for both linear heat conduction problems and linear elastic problems. This manuscript presents a simple nonlinear solver for the SDM analysis of heterogeneous materials. Although the solver can easily approximate the solutions to nonlinear multiscale problems, it does not require an iterative multiscale analysis at every convergence calculation. In other words, the proposed scheme does not completely interactively couple the multiple scales. We present numerical examples of nonlinear stationary heat conduction analyses of heterogeneous fields and compare the SDM model, the direct finite-element model, and the homogenized model based on the homogenization theory. For a real heterogeneous structure (graphite fiber composite) that did not have strong material nonlinearities, the SDM model using only 925 points gave a solution with similar precisions as an ordinary finite element solution using hundreds of thousands of nodes. To investigate the limitations of the method, we also applied the SDM to imaginary materials with various strengths of thermal property nonlinearities.

For real-time load monitoring, we present a new smart lighting protection skin using resistive touchpad techniques that covers measuring objects with a flexible sheet composed of multiple tiny sensors. We measured loading from off-plate direction, including quasi-static indentation and dynamic impact. We believe our method is suitable for load monitoring of composite aircraft structures. A metal film or mesh coving the fiber composite components of our system acts as both the load sensor and wiring, and a lightning protection shield (LPS). The sheet consists of an upper LPS layer and a lower layer, with multiple pressure-sensitive elastomer pills arranged between layers. The lower layer is a grid consisting of high-electrical-resistance nichrome wires and low-resistance copper wires. The pressure-sensitive pill becomes conductive when compressed. When the sensor sheet is indented, a compressed pill creates a new electrical path between the two layers and the electrical potential equalizes at that point. This event triggers the application of a potential across the nichrome wires that form the x axis, enabling measurement of the x coordinate. The orthogonal potential gradient is then applied to the lower layer so that the y coordinate can be measured. The x and y coordinates are recorded quickly and describe the quasi-static load point with an error of 29 mm or less. Additionally, we can estimate the peak value of the impact load by measuring the electrical resistance of the pressure-sensitive pill with an error of 17 %.

The stress intensity factor can be applied as an evaluation parameter of crack growth under small-scale yielding conditions. Moreover, the stress intensity factor corrected by the plastic zone correction can potentially be used as an evaluation parameter of crack growth for small-scale yielding criteria or beyond these criteria. In the previous study, the plastic zone correction method for that purpose was proposed. The method focuses on the gradient of the stress intensity factor at the crack tip, incorporating the term into the correction formula. To investigate the applicability of the correction experimentally, fatigue crack propagation tests were conducted in this study using three types of specimens with different gradients. The results show that the crack growth rate increased when the gradient was large although the effective stress intensity factor range was the same. This indicates that the gradient of the stress intensity factor at the crack tip affects the stress state in the vicinity of the crack tip and the crack growth rate increases as the gradient increases. When the correction of the stress intensity factor was applied, the crack growth rate could be evaluated independently from the gradient of the stress intensity factor. The correction is applicable around small-scale yielding criteria or beyond these criteria, but is not applicable under sufficiently large-scale yielding conditions.

In recent years, thermoplastic CFRP attracts considerable attention especially in aviation and automobile industries due to weldability of thermoplastic CFRP. Ultrasonic testing (UT) is commonly adopted as a testing method for inspecting weld parts although time cost on UT is thought to be problematic. Since eddy current testing (ET) is used for rapid inspection on electrically conductive materials, this paper presents an eddy current based approach for detecting defects in thermoplastic CFRP welded zones. However, it is difficult for conventional ET to detect delamination which is parallel to eddy current although delamination is one of the common forms of weld defect. To detect delamination in thermoplastic CFRP welded zones, new eddy current based approach which utilizes temperature characteristic of electrical conductivity is proposed. The proposal consists of two steps. Firstly, temperature difference between intact zones and defective zones is caused by heating the one side of the weld part. Secondly, the temperature difference is detected by ET utilizing temperature dependency of electrical conductivity.