It is well known that corrosion of steel reinforcement is one of the important factors affecting long-term durability of reinforced concrete (RC) and prestressed concrete (PC) structures. Corrosion usually occurs due to either carbonation or chloride attack. This has been well studied for RC, but not yet for PC. This experimental work is a case study on the long-term performance of prestressed concrete beam. Four prestressed concrete beam specimens including both post-tension type and pre-tension type (pre-cracked or without crack before the exposure) were tested. All beams have been exposed to the real marine environment at Sakata Port, Yamagata prefecture for 20 years, then transferred to the laboratory and stored in a constant temperature and sheltered from the rain for 15 years. Then they were transported to Kyushu University, Ito campus, and tested. Experimental test was addressed for corrosion state of prestressing wires / tendons and load bearing capacity of the beam specimens. This report presents the test results and discussion on durability of PC beam specimens.

In order to reduce the environmental impact, it will be important to make effective use of low-quality coarse aggregate to the extent that it satisfies the performance requirements of concrete. However, there are physical properties such as drying shrinkage and thermal expansion that cannot be captured by routine quality tests of coarse aggregate. In order to determine the drying shrinkage and thermal expansion coefficient of coarse aggregate, the authors have previously proposed a method to determine the length variation characteristics by directly attaching strain gauges to the coarse aggregate particles. In this study, we measured the temperature strain of low-quality coarse aggregate particles using strain gauges, which has not been clarified so far, and also investigated the method for calculating the coefficient of linear thermal expansion. As a result, it was clarified that even low-quality coarse aggregate particles can be measured by strain gauges to determine the temperature strain. It was also revealed that the coefficient of thermal expansion of low-quality coarse aggregate particles is not much different from that of normal-quality coarse aggregate particles, with no significant difference. Furthermore, it was found that the coefficient of linear thermal expansion of coarse aggregate particles can be roughly determined by using the test report attached to a commercially available strain gage. The calculated coefficient of thermal expansion of coarse aggregate particles by this method differs by a maximum of ±1 μ/°C from the exact coefficient of linear thermal expansion referring to quartz glass.

Aging of concrete structures has become a serious problem in Japan, and periodic maintenance is essential for preventing accidents caused by structural aging. In this study, a method for estimating defects in concrete from hammering test data on a concrete plate using machine learning was developed. A neural network based on Convolutional Neural Network, Residual Network and Self-Attention Network to estimate the three-dimensional position and size of the defects was constructed. Moreover, a dataset was created from the topology of the internal defects and the acceleration response waveform when a concrete plate was struck. The entire plate was represented as a nondimensional density matrix. The scalograms generated from the acceleration response waveform was used as the input. Furthermore, estimation was performed using acceleration response waveforms containing artificial noise. In this study, as a preliminary step to detecting internal defects in concrete structures based on machine learning using hammering response data, we conduct a study based on machine learning using hammering response data containing artificial noise, and evaluate machine learning models with high generalization performance.

A probabilistic evaluation for the creep rupture time of heat transfer tubes made from Super304H austenitic stainless steel in ultra-supercritical power plants is presented. A conventional assessment of creep life is based on deterministic evaluation method by using creep life prediction equation with constant values of stress and temperature. In the traditional assessment, estimated temperature is used due to the difficulty of temperature measurement of tubes exposed to combustion, and creep rupture time is evaluated conservatively due to variations of rupture time caused by heat-to-heat differences. In this study, assuming that the temperature uncertainty follows a normal distribution and the variation of creep rupture time follows a lognormal distribution, a Monte Carlo method and an approximate evaluation method are proposed to evaluate a creep rupture probability quantitatively. Then, the effect of temperature uncertainty on creep rupture probability was evaluated. Consequently, creep rupture probability at the rupture time obtained by the deterministic evaluation increases as the standard deviation of temperature increases. Furthermore, the result obtained by the Monte Carlo method is in good agreement with that of the approximate evaluation method.

Recently, metal bats have been widely used in high school and other baseball games, but owing to their improved performance, these bats have led to increased amount of accidents. Pitchers are often untimely hit the ball, resulting in serious injuries. However, the National Collegiate Athletic Association evaluates the repulsion performance of bats and balls using a standardized value called BBCOR (Bat-Ball Coefficient of Restitution). Thus, only bats with a value of 0.50 or less can be used. The BBCOR can quantitatively indicate the restitution performance of a bat, and several designs for controlling the BBCOR of metal bats have been proposed in previous studies. However, most of these require the bat to be actually manufactured; therefore, a simple method for predicting the BBCOR using dimensions and other factors during bat design is needed. In this study, the compressive load and BBCOR was first determined using simple compression and ball impact tests on aluminum alloy baseball bats with varying outside diameters and plate thicknesses. Subsequently, the relationship between the BBCOR and spring constant of the bats was examined, and the effects of the outside diameter and plate thickness on the spring constant were investigated. Based on these results, the effects of the outer diameter and plate thickness on the BBCOR were examined, and a simple equation that can determine the BBCOR from the shape (outer diameter and plate thickness) was proposed.

The global promotion of hydrogen refueling stations for fuel cell vehicles (FCV) is driven by the vision of achieving a Hydrogen Society. In Japan, a design pressure of 70 MPa has become the standard to enhance the cruise distance of FCV. However, this higher gas pressure increases the risk of hydrogen leakage from mechanical joints. Consequently, the infrastructure industry emphasizes the need to understand the hydrogen compatibility of welding joints to ensure the safer and more cost-effective operation of these facilities. This paper presents the results of slow strain rate tensile (SSRT) tests conducted in a high-pressure gaseous hydrogen environment to assess hydrogen embrittlement in austenitic stainless joints. During specimen preparation, U-grooves were machined at the edges of the plates, which were then butted together to form filler welded joints using Gas Tungsten Arc Welding (GTAW) with commercially available AWS ER 316L filler wire (high Ni-equivalent) under two different weld heat inputs (9.9 and 36.0 kJ/cm). The welded joints exhibited a low susceptibility to hydrogen embrittlement, despite the increase in the amount of crystallized delta ferrite in the weld metal with a decrease in the weld input. Based on the results, we conclude that the Type 316L welded joint with AWS ER 316L filler is suitable for various components in hydrogen refueling stations with the applied welding conditions. This valuable insight contributes to realizing safer and more reliable hydrogen refueling facilities while also reducing maintenance costs.

The macroscopic mechanical fatigue properties of negative electrodes in lithium-ion batteries and their estimation methods have been investigated based on a simple mechanical model. Tensile and bending fatigue tests were conducted on a negative electrode made of carbon powder and polyvinylidene fluoride (PVDF) binder. The simple model proposed in this study was used to estimate the stress and strain in the PVDF binder supporting the structure of the negative electrode. This model approximates the orientation of the carbon particles as the body-centered cubic (bcc) or the face-centered cubic (fcc), referring to the crystal lattice of metallic materials. The carbon particles in the model are bonded by the PVDF binder. The tensile fatigue test results showed that the negative electrode dissipated energy under the repeated loading, and the stress–strain curve showed hysteresis loops. The total dissipated energy of the binder obtained from the tensile fatigue test and the proposed simple model were used to estimate the mechanical fatigue life of the negative electrode with different binder ratios. The estimated S–N curve agreed with the mechanical fatigue life of the negative electrode with low binder ratios in the bending fatigue test.