Papers by Author: Yoshiharu Mutoh

Abstract: This study aims at experimentally revealing the effects of damages/fractures in HAp coating layer of acetabular cups on loosening behavior of the acetabular cups. Aseptic loosening is occurred due to degradation of fixing force of acetabular cups by biological effects or mechanical loading. However, effects of mechanical loading on loosening behaviour have not been observed yet. In order to simulate cyclic loading conditions of gaits, a testing system which can load entire components of joint including acetabular cups and stem parts was designed. Moreover, by applying two positions of AE sensors during fatigue testing, it was possible to observe the damage behavior of HAp coating. AE measurement detected different failure modes of HAp coating, which were locally occurred at an edge part of the acetabular cup due to stress singularity at that region. In the cases of changing fixation angles, even though damages in simulated cancellous bone surrounding acetabular cups were less occurred, extents of rotational displacements were compatible with the one in an original fixation angle.

Abstract: Biomaterials containing calcium phosphate ceramics have been used as bone substitute materials. In this study, the compressive strength and in vitro bioactivity tests of hydroxyapatite (HAp) from golden apple snail shell mixed with calcined kaolin (CK) were investigated for used as bone substitute materials. Mixed paste samples were cured at 23°C and 60°C for 2 days and curing continued at 23°C for 7 days. The effects of HAp:CK weight ratio on compressive strength and apatite formation in simulated body fluid (SBF) were investigated. The good compressive strength was 32.93 MPa at 25 % hydroxyapatite with 75% calcined kaolin at curing temperature of 60°C. Apatite formation was observed on sample surfaces after soaking in SBF for 28 days using SEM, EDS and XRD analyses. It was found that apatite formation took place on the surface of samples, consisting of HAp, after immersion in SBF.

Abstract: The effects of mixing conditions, i.e; mixing speed and mixing duration on the mechanical properties of the magnesium based composites were investigated. The hardness, tensile strength and microstructure of composites were studied. It was found that increase of the mixing speed and prolong the mixing time can improved the distribution of SiC particle and mechanical properties of magnesium based composites.

Abstract: Tensile and fatigue tests of two compositions of steels, Fe-0.6%C-l.7%Cu and Fe-0.8%C-2.1 %Cu sintered at wide range of temperatures from 900°C to 1200°C were carried out to investigate effects of element content and sintering temperature. When the sintering temperature was higher than 1100°C, Fe-0.8%C-2.1%Cu steel exhibited higher density, tensile strength, elongation and fatigue strength compared to the other steel. The higher Cu content results in the higher density because Cu contributes to liquid phase in the sintering process. The higher C content contributes to the higher tensile strength, elongation and fatigue strength due to formation of pearlite phase. When the sintering temperature was lower than 1000°C, density, tensile strength and elongation were low. However, the metal copper phase still remains after sintering.

Abstract: The bolt load loss behavior of AZ91D magnesium alloy bolted joints with a conventional SCM435 steel bolt and an A5056 aluminum bolt was investigated at elevated temperature. The A5056 bolt could reduce the bolt load loss compared to the SCM435 bolt due to smaller mismatch of thermal expansion between the bolt material and the plates. The mismatch of thermal expansion between bolt material and AZ91D plates was found to induce the compressive creep deformation in the AZ91D plates which performed as the main mechanism of bolt load loss. At higher tightening stress, the bolt load loss could be intensified by additional plastic deformation in bolt occurred during the test. Moreover, it is suggested that the plastic deformation could be reduced by decreasing the friction condition in the bolted joint.

Abstract: Tensile and compressive creep tests of the extruded magnesium alloy AZ91D were carried out in vacuum at 150°C under constant engineering stresses ranged from 60 to 150 MPa. From the test results, the secondary creep rate in tension was found to be significantly higher than that in compression. Moreover, the estimation method of creep curve under a constant true stress was proposed by considering the reduction of cross sectional area during tensile loading where the specimen cross-sectional area and length were measured periodically until the end of creep test. The creep curve under a constant true stress obtained in the present study was still different between tensile and compressive loadings. Therefore, it should be noted that the different creep curves and creep exponents should be used in the creep deformation analysis of structures.

Abstract: Plasma sprayed Hydroxyapatite (HAp) coating on commercially pure titanium (cp-Ti) is widely used as implant materials. In this study, fatigue behavior of as-sprayed HAp top coat with HAp/Ti bond coat specimen under ambient environment (A-HTi) as well as under simulated body fluid, SBF, environment (I-HTi) at 36.5°C was investigated by four point bending fatigue test at a stress amplitude of 170 MPa under various frequencies. In order to investigate apatite precipitation during fatigue loading, the test specimen was immersed in SBF at 36.5°C during the fatigue test. For comparison, the test specimen was immersed in SBF at 36.5°C for a day to a week without fatigue loading and then the fatigue test of the immersed specimen was carried out under ambient environment (I-A-HTi). The fatigue loading would not influence the apatite precipitation in the HAp coating layer of the specimen. The fatigue lives of the I-HTi and I-A-HTi specimens were shorter compared to that of A-HTi specimen. The shorter fatigue lives of the I-HTi and I-A-HTi specimens would result from the attack of SBF on titanium substrate. However, the apatite precipitation in the coating layer up to one week immersion did not significantly influence the delamination between HAp top coat and cp-Ti substrate under the bending fatigue.

Abstract: High reliable hydroxyapatite (HAp) coating on commercially pure titanium (cp-Ti) substrate with and without mixed hydroxyapatite/Titanium (HAp/Ti) bond coat was successfully developed by using plasma spraying. The four-point bending with Acoustic Emission attachment (AE) for evaluating failure behavior of the two kinds coated specimens was conducted to investigate the effect of bond coat layer on failure of the coating. The effect of apatite precipitation by immersing in conventional simulated body fluid (c-SBF) on failure behavior of the coated specimens were also investigated. The AE patterns obtained during four-point bending test of the specimens with apatite precipitation after immersion in c-SBF was compared with those of the specimens without apatite precipitation. After a week immersion in c-SBF, the AE patterns obtained from four-point bending test of HAp top coating specimens with and without bond coat clearly showed faster failure of the coating compared to those without c-SBF immersion. In addition, under c-SBF, the bond coating contributed to the retarded failure of the HAp top coating compared to that without bond coat. From XRD analysis, the as-sprayed layer composed of HAp coexisted with CaO. After c-SBF immersion, CaO dissolved into c-SBF and the as-sprayed HAp top coating changed to bone-like apatite which might contribute to the faster failure of the coating.

Abstract: High temperature tensile test was conducted to study high temperature properties of the magnesium based composites reinforced with SiC particulates and monolithic magnesium as well. It was found that tensile strength of monolithic magnesium and Mg-SiC composites decreased with an increase in testing temperature. While the elongation to failure both samples were increased when increasing temperature. At all testing temperature, the tensile strength of the composite sample was found to be superior compared to monolithic magnesium due to presence of SiC particulates and efficiency of spark plasma sintering process in fabrication of the composites.

Abstract: This paper describes for verification of bending effect on the performance of the heightwise-asymmetric plunge cutting method, which was composed of an upper-wedge blade and a lower-wedge blade embedded in the lower-counter plate, in order to apply this cutting method for a polycarbonate (PC) thick sheet. By varying the tip angle α_U and the tip thickness w_U of lower blade embedded in the counter plate, and combining a standard steel cutting rule of 42° center bevel blade, the sheared profile of two kinds of PC worksheet (the thickness of which was chosen as t=0.5, 1.0 mm) was experimentally investigated. Through this experiment, it was found that the sheared profile (the necked height η_n, the upper inclination angle β, the lower inclination angle β_U) of PC worksheet was primarily characterized by the normalized lower tip thickness w_U/t. The difference of sheared profile was explained using the Prandtls punching solution for two kinds of PC worksheet. Furthermore, by varying the heightwise position of lower blade tip, the bending effect on sheared profile of worked sheet was experimentally verified.