1999 Fiscal Year Final Research Report Summary
Fracture mechanics approach on evaluation of residual strength of structural timbers having a crack which emanates in moisture non-steady state condition
| Project/Area Number |
10660160
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
林産学
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| Research Institution | Shizuoka University |
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Principal Investigator |
SOBUE Nobuo Shizuoka University, Fac. Agriculture, Professor, 農学部, 教授 (50023495)
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| Co-Investigator(Kenkyū-buntansha) |
SATOH Kiyoshi Mie University, Fac. Education, Professor, 教育学部, 教授 (80006444)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Wood / Fracture mechanics / Crack / Creep fracture / Moisture steady state / Moisture non-steady state |
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| Research Abstract |
1. Creep and fracture of wood having a crack under humidity steady state
Compact tension specimens designed by an ASTM standard were subjected to tensile stress perpendicular to a crack surface. Sugi and hemlock were used. Creep tests were done under stress levels from 45 % to 85% of maximum load. Crack opening displacement, acoustic emission(AE), clack length, humidity and temperature were measured simultaneously during tests. A life time of a specimen during a creep failure can be estimated by a minimum creep speed of COD during a steady creep stage. Above stress level of 60%, AE was detected frequently at initial creep stage and before catastrophic fracture. A few AE was also detected during steady creep stage. A creep limit was estimated to be below a stress level of 50%, because no AE was detected at this stress level.
2. Creep and fracture of wood having a crack under humidity non-steady state
Creep tests of sugi under natural environmental condition were conducted. Fracture occurred relatively low stress level, below 40%. Crack propagation occurred when high humidity condition continued in such as a rainy day. COD creep curves showed daily cyclic change, however, a mechano-sorptive phenomenon which commonly occurres at a clear wood specimen was not observed. Inner stress induced by moisture absorption increased a stress intensity factor near a crack tip, and it accelerated a crack propagation.
3. Effect of loading speed and modelization by a stress relaxation test
Effect of loading speed on fracture of wood having a crack was tested. Speed effect on load-COD diagram was explained by stress relaxation tests and a modelization using a Maxwell model. A fracture criterion based on elastic component of AE was proposed to characterize a critical condition.
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