Tohru Takamatsu

Fatigue Crack Growth Properties of a GLARE3-5/4 Fiber/Metal Laminate

Abstract The objective of this study is to investigate the properties of fatigue crack growth in GLARE3-5/4 fiber/metal laminate and the validity of two methods for analyzing the fatigue crack growth of fiber/metal laminates. GLARE3-5/4 consists of five thin sheets of 2024-T3 aluminum alloy and four layers of (0/90) glass/epoxy. Centrally notched specimens were fatigue tested under constant amplitude loading and crack length was measured using the DC potential-drop method. The size of the delamination produced between aluminum alloy sheets and fiber-adhesive layers was measured from ultrasonic C-scan pictures taken around the fatigue crack. The test results indicated the features of fatigue crack growth in GLARE3-5/4. The validity of the two methods for analyzing the fatigue crack growth of fiber/metal laminates is discussed based on the test results.

Evaluation of fatigue crack growth behavior of GLARE3 fiber/metal laminates using a compliance method

Abstract The objectives of this study were to investigate the effectiveness of a compliance method for analyzing the fatigue crack growth of GLARE3 fiber/metal laminates. The materials tested were GLARE3-5/4 (2.6 mm thick) and GLARE3-3/2 (1.4 mm thick). Centrally notched specimens with two kinds of notch length and two kinds of fiber orientation were fatigue tested under constant amplitude loading. The expression of the experimental stress intensity factor, K exp , for the 2024-T3 aluminum-alloy layers of a GLARE3 is formulated and K exp were obtained from the relationship between crack length and specimen compliance. The test results clarified the following: (1) d a /d N –Δ K exp relationships roughly show the linear relationship independent of the maximum stress level, specimen thickness, notch length, and fiber orientations, (2) the d a /d N –Δ K exp relationships approximately agree with the linear part and its extension of Paris–Erdogan’s law obtained for the d a /d N –Δ K relationship of the 2024-T3 aluminum-alloy, (3) the compliance method is effective for analyzing fatigue crack growth in GLARE3 laminates.

Effects of laser heat treatment on mechanical properties of ceramic coated steelsPart 2 – Fracture strength of laser heat treated ceramic thin film

Abstract In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness. However, the effects of laser heat treatment on the fracture strength of ceramic thin films were not investigated yet. In the present research, in order to demonstrate further development of this method, the fracture strength of laser irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat induced changes in the substrate hardness, a cemented carbide WC–Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. The application of laser heat treatment for the substrate quenching after coating process can effectively prevent the fracture strength loss of ceramic thin film.

Effects of heat treatment on mechanical properties of ceramic thin films

In our previous studies, we found that heat treatment after coating with TiN could be an effective method to improve the mechanical properties of TiN-coated steel. However, it was not clear whether a similar effect could be obtained for other types of ceramic thin films. The heating temperature condition suitable for improvements of various thin films also has not yet been revealed. In this study, for three kinds of ceramic thin films, TiN, TiAlN and CrN, deposited on steel substrates by an arc ion plating method, heat treatment was carried out at various temperatures ranging from 733 to 1333 K, and the effects of heat treatment and heating temperature on mechanical properties of these films were investigated. For all films, the adhesive strength was improved effectively by heat treatment. This improvement could be explained by the formation of a diffusion layer between the film and the substrate in the heat treatment process. Wear resistance was also improved by heat treatment in all the films, though hardness decreased. It was also found that the friction coefficient in each film was decreased by the heat treatment, and this decrease in friction coefficient could be one reason why wear resistance was improved.

Effect of Crack Opening on Distribution of Magnetic Flux Density around Fatigue Cracks

In order to identify the mechanisms of changes in the magnetic flux density distribution around fatigue cracks that occur during crack propagation, JIS SCM440 specimens were fatigue tested, and the relation between crack morphology and magnetic flux density distribution was investigated. Two features were observed: a high intensity area around the crack tip, and a low intensity area around the crack root. The low intensity area grew larger for wide open cracks and disappeared when the crack was closed by external force. It was hence found that the magnetic flux density distribution is strongly affected by the crack opening.

Effect of Sputtering Gas Pressure and Bias Voltage on Mechanical Properties of TiN Coating Deposited by DC Magnetron Sputtering

The mechanical properties of TiN films deposited on carbon steel JIS S45C by reactive dc magnetron sputtering under three sputtering gas pressures, 0.5Pa, 0.8Pa, and 1.76Pa were investigated. The residual stress once increased and then decreased with increasing bias voltage at 0.5Pa and 0.8Pa, but increased monotonously at 1.76Pa. These variations could be explained by the variations of the bombarding energy of a sputtered ion at each gas pressure. The variations of hardness and toughness correlated with the variation of residual stress. The variation of adhesive strength also could be explained by the variation of the bombarding energy with a model proposed in this study. A specific wear rate was also investigated, and it was found that to increase not only the hardness but also the adhesive strength is necessary to improve the wear resistance of TiN films.Copyright

Delamination initiation life and growth behaviour of ceramic coated steels quenched after coating process under rolling contact loading condition

Abstract In order to investigate the effects of a new surface modification method, ‘the substrate quenching after coating’ on the rolling contact fatigue strength, TiN coated steel specimens and CrAlN coated steel specimens were processed by this method and the thrust type rolling contact fatigue tests were carried out for these specimens. In the process of the substrate quenching after coating, two types of quenching methods, furnace quenching and laser quenching, were used. For the furnace quenched specimens, the delamination initiation life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidisation of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the delamination initiation life of the laser quenched specimens was longer than that of the furnace quenched specimens. After the initiation, the delamination of the furnace quenched specimen grew much faster than that of laser quenched specimen. These reasons could be explained by the difference of the process time of the furnace quenching and the laser quenching. The process time, in which the ceramic coating of the specimen was exposed to an elevated temperature, of the furnace quenching was much longer than that of laser quenching. It is considered that substrate laser quenching after coating could be an effective way to improve the delamination initiation life and to reduce the delamination growth rate under rolling contact fatigue.

Flaking Initiation Life under Rolling Contact Fatigue of Ceramic Coated Steels Quenched after Coating Process

In our previous studies, a new surface modification method by combination of ceramic coating and heat treatment, named “substrate quenching after coating” was developed. The thrust type rolling contact fatigue tests were carried out for TiN coated steels and CrAlN coated steels processed by substrate quenching after coating, and the effects of the type of ceramic coating (TiN or CrAlN) and the quenching methods (by furnace quenching or by laser quenching) on the flaking initiation life were investigated. For the specimens quenched by furnace, the flaking life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidization of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the flaking life of the specimens quenched by laser was longer than that of the specimens quenched by furnace. This reason could be explained by the difference of the process time of the furnace quenching and the laser quenching. It is considered that laser quenching after coating could be an effective way to improve the flaking initiation life under rolling contact fatigue.

Influence of Laser Heat Treatment on Fracture Strength of Ceramic Thin Film

In our previous study, it has been shown that improvement of the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness can be achieved by applying laser quenching. In the present research, in order to demonstrate further development of this method, the fracture strength of laser-irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat-induced changes in the substrate hardness, a cemented carbide WC-Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. Laser quenching has been shown to effectively reduce the fracture strength loss of the ceramic thin films in coated steels.

Evaluation of Fatigue Damage in Coarse-Grained Aluminum With Scanning X-Ray Energy Dispersive Diffraction Microscope

Based on the Berg-Barrett method, Scanning Energy Dispersive X-ray Diffraction Microscopy (SEDXDM) has been developed for nondestructively evaluating both the surface and subsurface of poly-crystallized materials. The SEDXDM includes an X-ray source generating continuous X-ray spectrum as a key component to form a highly resolved 2-D horizontal cross-sectional digital image. This article presents the evaluation of the fatigue damage (e.g., slip line and slip band caused by fatigue deformation) of the coarse-grained aluminum, which is made by means of annealing and has been repeatedly bent to generate the stress and make the slope of the stress created in the thickness direction of the plate specimen, under fully reversed anti-plane bending condition with the SEDXDM.© 2004 ASME