FATIGUE BEHAVIORS OF CEMENT MORTAR SPECIMENS UNDER REPEATED IMPACT BENDING LOAD

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  • 繰返し衝撃曲げを受けるモルタル試験体の疲労挙動について
  • クリカエシ ショウゲキ マゲ オ ウケル モルタル シケンタイ ノ ヒロウ キ

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Abstract

The purpose of this investigation is to examine the S-N diagram and the fatigue process, and the fracture toughness of cement mortar specimens under repeated impact bending load. Here, S is impact load level and N is numbers of repeated stroke. This investigation is divided into three tests. The S-N diagram of cement mortar specimens was clarified by the first test which we struke the falling ball with stell on the center of simple beams (shape of beam = 4×4×16cm, span = 15cm) to obtain impact fatigue life data. The second test is the fatigue process test which was performed by the same method as the first test to obtain the relation between numbers of repeated stroke and impact flexural strain, and residual strain as well. The third test is the fracture mechanics test which was performed on two simple beams with notch and without notch to clarify the crack propagation process under repeated impact bending load and to expect impact fatigue life of cement mortar specimens. The main results obtained by this investigation are summarized as follows. (1) From the first test, relations between S and N can be showen by two straight lines on the S-N diagram. When S is larger than an intersecting point which is named the specific impact load level S_0, the impact breakage is the predominant behavior on the S-N diaram. When S is smallar than S_0, impact damage is very little, then the fatigue process ia observed. Here, S_0 is about 55 % of impact bending strength. (2) In the case of S>S_0, the crack propagation under repeated impact bending load is in proportion to S and the propagation process of impact flexural strain and residual strain change remarkably. Therefore, the fatigue process under repeated impact bending load can be estimated by the crack propagation and impact flexural strain and residual strain. (3) When the linier fracture mechnics applies to cement mortar specimens under repeated impact bending load, the fatigue life of specimens, that is, the crack propagation curve and numbers of repeated stroke into fracture, is estimated by statical stress intensity factor K and physical constant c and m. Here, the values of c and m can be obtained by the experimental results.

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