Spin scrubber for 12-inch wafer uses a high speed robot system to fetch and load the wafer for cleaning process. This fast movement of the robot sometimes causes an undesirable vibration leading to an accident such as it drops the wafer during the transfer motion. Topology optimization is performed to find an optimal shape of the robot arm and reduce the excessive vibration using homogenization method. Experimental vibration diagnosis by measuring the acceleration signal during picking and placing motion is performed to evaluate the characteristics of vibration. Modal analysis for the robot arm is also conducted using FEM and compared with the experimental results. The first bending mode appears to be most important, so that the lowest natural frequency of the arm is increased to reduce the vibration level. Based on the dynamic modification by the topology optimization, several types of the optimal robot arm are designed and tested to prove the effectiveness of the optimal shape for the vibration suppression.

Scanning acoustic microscopy (SAM) has been applied successfully to measure leaky surface wave(LSAW) velocity from V(z) curve for material characterization. Besides LSAW, SAM produces a variety of wave modes in the material propagating with different phase speeds and features, one of which is the mode-converted ultrasound. In this paper, a novel method for simultaneous measurement of longitudinal and transverse acoustic wave velocities using the mode-converted ultrasound is developed and studied at SAM. Each ultrasound arriving at the acoustic lens with different speed and phase (or time-of-flight (TOF)) is measured by the defocused transducer to calculate longitudinal and transverse wave velocities. Simple mathematical ray analysis for the mode conversion is conducted to determine the relationship of acoustic velocities with TOF of the waves in plate. Experimental results for metals and glass show that the longitudinal and transverse wave velocities measured by the proposed method are as accurate as maximum 3% in error.

This paper deals with the stress singularity induced at the interface corner between the viscoelastic thin film and the elastic substrate as the film absorbs moisture from the ambient environment. The thin film is assumed to be a linear viscoelastic material and moisture effects are assumed to be analogous to thermal effects. The time-domain boundary element method is employed to investigate the behavior of interface stresses. The order of the singularity is obtained numerically for a given viscoelastic model. The numerical results exhibit the relaxation of interface stresses and large stress gradients are observed in the vicinity of the free surface. It is shown that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model considered.

Epoxy coating in nuclear fuel storage degrades with aging and hazardous radiation. In order to evaluate the deterioration of the epoxy, the dependence of acoustic impedance on mechanical properties is studied. Unlike metals, the epoxy is hard to measure the acoustic velocity because the surface of epoxy coating applied on a concrete wall is wavy and highly attenuative for the ultrasound. In this paper, simulated annealing (SA) algorithm is used to calculate the acoustic impedance using a multiple reflection waves from the rough epoxy surface. Epoxy films coated on small concrete cubes are subjected to the accelerated aging conditions and tested by SA method to calculate acoustic impedance of the epoxy film. The experimental results show that the acoustic impedance has a good correlation with the degradation of epoxy coating and the method developed in this study can be applied effectively to monitor the aging of the epoxy coating in the nuclear fuel storage.

High-tension bolts have been used widely for the clamping of many kinds of large structures. In these bolts, the estimation of clamping force has been regarded as the main issue in the evaluation of clamping condition. This paper proposes a method using ultrasonic wave, which is based on the dependency of sound speed on the stress. In order to verify the usefulness of the proposed method, two kinds of experiments are carried out. The first one involves the measurement of sound speed when the bolt is stressed by the tension tester, and here, the relationship between the exact axial force and sound speed is calibrated. The result shows good agreement with the expected linear relationship between sound speed and axial stress. The second experiment involves the measurement of axial stress by the proposed method when the bolt is stressed by the torque wrench. The results are coincident to the strain gage measurement. From these results, we can conclude that the proposed method is indeed useful in evaluating clamping force in high-tension bolts.