Gang Deng

Surface Temperature Calculation and its Application to Surface Fatigue Strength Evaluation

In recent years, power transmission gears for vehicles run at higher speeds and loads and are accompanied by very high surface temperatures. Under such a high surface temperature condition, the surface strength cannot be evaluated correctly only by the use of Hertzian stress. This research attempts to introduce a new surface strength evaluation method considering the surface temperature rise. First, the surface temperatures of rollers under different rolling and sliding conditions are measured using a thermocouple. The effects of load P, mean tangential velocity V m and sliding velocity V s on surface temperature are investigated and analyzed. Then, an experimental equation is presented which shows the linear relationship between surface temperature and G R P 0.86 V 1.31 s V -0.83 m value. Based on the comparisons between calculated and measured tooth surface temperatures, this equation is confirmed applicable to gear tooth surface temperature evaluation as well. A surface temperature index is proposed for surface strength evaluation. The relationship between the surface temperature index and the number of load cycles of the rollers is investigated. The results indicate the possibility to evaluate the surface strength based on the surface temperature.

Practical Methods for Crack Length Measurement and Fatigue Crack Initiation Detection Using Ion-Sputtered Film and Crack Growth Characteristics in Glass and Ceramics

A crack length measurement method is very important in the investigation of the fatigue crack growth characteristics of a material and in the evaluation of the fatigue strength of a machine element. Many crack length measurement methods have been proposed. Brown et al. (1966) and Nishitani et al. (1985) measured crack length through the changes in the displacement and compliance of the test piece. Ashida et al. (1996) and Nakai et al. (1989) investigated the changes in electrical properties around a crack during its growth. Lee et al. (1985) and JSME (1986) recommended estimating the crack length from the opening or closing displacement of a crack. In addition, crack length can also be measured by using an optical microscope, an optical grid technology (Bucci et al., 1972, Maustz et al., 1976, James et al., 1981), an acoustic emission method (Masuyama et al., 1994) and an ultrasonic method (Shimada et al., 1983). However, the methods proposed up to now require specific measuring apparatuses and complex calculation processes for crack length, and are applicable to long cracks several millimeters in length, not to small cracks shorter than 1mm in length or cracks with a high growth rate. In addition to the above-mentioned methods, a thin metal film, such as a crack gauge (e.g., KV-25B manufactured by Kyowa Co.), has been used for crack length measurement and fatigue crack initiation detection in some machine elements, such as gears, where cracks are up to several millimeters in length (Deng et al., 1991). Since this metal film is formed on a plastic base film with a thickness of about several tens of micrometers, there is a relatively large error between the actual and measured crack lengths. Increasing the measurement accuracy of the film can only be achieved by decreasing the thicknesses of the metal and plastic base films. An ion-sputtering device, widely used in a scanning electron microscopy system, is a coating device used to form a nanoscale-thickness metal film on a surface. In this chapter, we introduce methods for crack length measurement using an ion-sputtered film, which are considered as ideal and practical methods applicable to micro-cracks or small cracks in glass

Quantification of the sit-to-stand movement for monitoring age-related motor deterioration using the Nintendo Wii Balance Board

Simple methods for quantitative evaluations of individual motor performance are crucial for the early detection of motor deterioration. Sit-to-stand movement from a chair is a mechanically demanding component of activities of daily living. Here, we developed a novel method using the ground reaction force and center of pressure measured from the Nintendo Wii Balance Board to quantify sit-to-stand movement (sit-to-stand score) and investigated the age-related change in the sit-to-stand score as a method to evaluate reduction in motor performance. The study enrolled 503 participants (mean age ± standard deviation, 51.0 ± 19.7 years; range, 20–88 years; male/female ratio, 226/277) without any known musculoskeletal conditions that limit sit-to-stand movement, which were divided into seven 10-year age groups. The participants were instructed to stand up as quickly as possible, and the sit-to-stand score was calculated as the combination of the speed and balance indices, which have a tradeoff relationship. We also performed the timed up and go test, a well-known clinical test used to evaluate an individual’s mobility. There were significant differences in the sit-to-stand score and timed up and go time among age groups. The mean sit-to-stand score for 60s, 70s, and 80s were 77%, 68%, and 53% of that for the 20s, respectively. The timed up and go test confirmed the age-related decrease in mobility of the participants. In addition, the sit-to-stand score measured using the Wii Balance Board was compared with that from a laboratory-graded force plate using the Bland–Altman plot (bias = −3.1 [ms]-1, 95% limit of agreement: −11.0 to 3.9 [ms]-1). The sit-to-stand score has good inter-device reliability (intraclass correlation coefficient = 0.87). Furthermore, the test–retest reliability is substantial (intraclass correlation coefficient = 0.64). Thus, the proposed STS score will be useful to detect the early deterioration of motor performance.

Effect of Acetabular Reinforcement Ring With Hook for Acetabular Dysplasia Clarified by Three-Dimensional Finite Element Analysis

The objective of this study was to biomechanically determine the effect of the severity of acetabular dysplasia, number and positions of screws and type of bone graft material used on the initial fixation strength of the acetabular reinforcement ring with hook (Ganz ring) using the finite element method. Relative micromotion increased as the severity of acetabular dysplasia increased and tended to decrease as the number of screws increased, but varied according to screw placement position. Increased strength of the bone graft material led to decreased relative micromotion. Biomechanically, the Ganz ring can be placed securely using 3 screws in patients with Crowe 1 dysplasia. However, in patients with Crowe 2 or higher dysplasia, it is necessary to spread at least 4 screws across an area of good host bone.

Fatigue Crack Length Measurement Method with an Ion Sputtered Film

The purpose of this research is to show a simple and high precision method to measure the length of a crack as well as a micro crack using an extremely thin ion sputtered film. An ion sputtered grid film was proposed to measure the crack length for a bending test specimen. Based on the comparisons between the measurement results and that by an optical microscope, the ion sputtered gird film has a very high measurement precision. This method is considered convenient and practicable for the crack length measurement of insulating materials such as ceramics. Meanwhile, an one-piece ion sputtered film was used on a metal bending specimen, the possibility to apply the ion sputtered film in the crack length measurement of a metal machine element was confirmed by the change of the electric resistance of the film with crack growth.

Finite element analysis of the tibial bone graft in cementless total knee arthroplasty

BackgroundAchieving stability of the tibial implant is essential following cementless total knee arthroplasty with bone grafting. We investigated the effects of bone grafting on the relative micromotion of the tibial implant and stress between the tibial implant and adjacent bone in the immediate postoperative period.MethodsTibial implant models were developed using a nonlinear, three-dimensional, finite element method. On the basis of a preprepared template, several bone graft models of varying sizes and material properties were prepared.ResultsMicromotion was larger in the bone graft models than in the intact model. Maximum micromotion and excessive stress in the area adjacent to the bone graft were observed for the soft and large graft models. With hard bone grafting, increased load transfer and decreased micromotion were observed.ConclusionsAvoidance of large soft bone grafts and use of hard bone grafting effectively reduced micromotion and undue stress in the adjacent area.

Evaluation of Stress Shielding for Three Types of Implanted Femurs Based on Stress Distribution

This research investigates the stress distribution of the three types of implanted femurs using the finite element method analysis. The comparisons of the stress distribution between the implanted femursand the healthy femur were performed and the characteristics in the stress shielding of each casewere clarified. Since the load is transferred on the contact surface between the implant and the inner surface of the femur in the case of the total hip arthroplasty, the stress in the intertrochanteric zone (Gruen zone 7) become very small, and the phenomenon of the stress shielding is confirmed obviously. The stress distributions of the femurs afterthe resurfacing hiparthroplasty and the thrust plate prosthesis are about the same with that of the healthy femur, so, the possibility of the stress shielding is considered lower compared with the femur after the total hip arthroplasty. However, considering the stress concentration thatwill increase the risk of femoral fracture caused by the screws for the fixation of the implant in the thrust plate prosthesis, the resurfacing hiparthroplastymay beconcluded as the best method among these three types of implants to avoid stress shielding.

Effects of Surface Roughness and Abnormal Surface Layer on Fatigue Strength

The purpose of this research is to evaluate the effects of surface roughness in normalized steel and the effects of abnormal surface layer in carburized steel on the fatigue strength that is considered as the limit of no crack initiation. Normalized and Carburized test pieces with crowned round notches were used in the fatigue tests, the normalized test pieces have different surface roughnesses and the carburized test pieces have different surface microstructures on the notch surface. The changes in fatigue strength due to the differences in the notch surface roughness and surface microstructure were investigated. As the conclusions, fatigue strength will be certainly increased by decreasing the surface maximum height, and removing the abnormal surface layer formed during carburized treatment leads to a marked increase in fatigue strength.

Evaluation of the crack growth characteristics of glass and ceramics based on crack length measurement using an ion-sputtered film

The crack length measurement method using an ion-sputtered film, proposed by the authors based on the change in the electric resistance of the film during the crack growth, was applied to the small crack growing in soda lime glass and alumina ceramics. Since the measurement system can record the electric resistance of the ion-sputtered film at a high sampling frequency of 125kHz, the crack lengths was measured almost continuously, and the relationship between the crack growth rate and the stress intensity factor were obtained in the whole regions from low crack growth rate to brittle fracture. The growth characteristics of the small crack under 1mm in alumina ceramics are clarified to be different from that of the large crack in the same materials; for example, the n values, which is defined as the constant in the Paris law relating the crack growth rate to the stress intensity factor, in the soda lime glass and the alumina ceramics obtained by this research are 74 to 96 and 530 to 580 respectively in the region I, and 12 to 15 and 17 to 25 respectively in the region II, that are different from the values obtained from a large crack, especially for the alumina ceramics.