Relationship between heat treatment and fatigue crack extension properties demonstrated on the dental alloy casting used as the compact-type specimen
Grant-in-Aid for Scientific Research (C).
|Research Institution||Tokyo Medical and Dental University|
NAKAMURA Hideo Tokyo Medical and Dental University, Faculty of Dentistry assistant, 歯学部, 助手 (60172425)
MOTOMURA Kazuo Tokyo Medical and Dental University, Faculty of Dentistry assistant, 歯学部, 助手 (60272598)
TAKAHASHI Hidekazu Tokyo Medical and Dental University, Faculty of Dentistry assistant professor, 歯学部, 助教授 (90175430)
NISHIMURA Fumio Tokyo Medical and Dental University, Faculty of Dentistry professor, 歯学部, 教授 (10013856)
|Project Fiscal Year
1998 – 1999
Completed(Fiscal Year 1999)
|Budget Amount *help
¥3,200,000 (Direct Cost : ¥3,200,000)
Fiscal Year 1999 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1998 : ¥2,400,000 (Direct Cost : ¥2,400,000)
|Keywords||fatigue crack development / dental alloy / casting / compact-type specimen / heat treatment / 疲労亀裂進展 / 歯科用合金 / 鋳造体 / コンパクト試験片 / 熱処理|
Outline of our research performance
In an object to determine causes of the fact that fatigue strength demonstrated no alterations owing to heat treatment, any relationship between extension speed of fatigue crack and stress intensity factor as well as effective stress intensity factor range was researched depending on the heat treatment process.
<<Materials and methods>>
1. A casting pattern was produced from an acrylic plate, placed in the center of a casting ring, and invested conventionally with a gypsum-bonded investment material. The investment was, after setting, heated for 30 minutes at 100°C and for one hour at 300°C and then maintained for 30 minutes at 700°C. Then it was cast and allowed to cool down to the room temperature prior to devesting. The casting was cleaned with a surface cleaning agent in a ultrasonic cleaner for removing the oxidized layer and the compact test specimen was finally finished from this casting in accordance with ASTM-E647 specificati
on by the wire electro-discharge machining. A heat treatment was conducted on the specimen as indicated by the alloy manufacturer.
2. The crack extension length was measured from the cracks on the fractured part by 100 times power of magnification with the CCD video camera (VS-60, Mitsubishi Chemical).
3. Stress intensity factor was calculated in accordance with ASTM-E647 specification. And effective stress intensity factor range was determined through the load division elasticity compliance method. With this method, the load magnitude of the crack opening was to be established by using the substraction circuit of the strain signal and the load bearing signal from the foil strain gauge (FLK-217-1L, Tokyo Sokki Laboratory) which was attached to the rear surface of the sample.
4. Fatigue tests were conducted on a hydraulic servo dynamic testing machine manufactured by Instron (8501, Instron) for loading failure stresses repeatedly under the room temperature atmosphere with repeated sign wave as the load waveforms at frequency of 5 Hz, maximum loading of 50〜77.4 kgf, and stress ratio of 0.1.
<<Results and Discussion>>
The cracks extended throughout the center of the specimen although slight irregularities exhibited. The crack extension speed was approximately 3 X 10ィイD17ィエD1 m/cycle at the effective extension intensity factor range of 15 MPamィイD11/2ィエD1 near around the fractured area, and no significant difference owing to heat treatment was observed. Probable reasons for above results are considered as follows :
1. Variation was found to be significant in consequence of using the cast specimen.
2. initial crack extension was not established in consequence of greater load magnitude of fracture stress.
Future testing will be scheduled by increasing numbers of test specimens.
(This research was reported at the 34th Congress Meeting of the Japanese Society for Dental Materials and Devices.) Less
Research Output (3results)