This paper reports the effects of fiber breakage defects and waviness defects on the compressive fatigue behavior and the progressive damage evolution process of 3D Multiaxial Braided Composites (3DMBCs). Combined wit...This paper reports the effects of fiber breakage defects and waviness defects on the compressive fatigue behavior and the progressive damage evolution process of 3D Multiaxial Braided Composites (3DMBCs). Combined with finite element compression simulation and ultra-depth microscope, the internal defect content of composites with different braiding angles was determined. The results demonstrate that the weakening effect of waviness and fiber breakage defects is greater than the strengthening effect of the braiding angle. This causes the fatigue resistance of 3DMBCs with the 31° braiding angle being better in both directions of 0° and 90°. The increase of 4° waviness and 10% fiber breakage defect results in the average fatigue life of composites being shortened by 48% and the energy consumption rate increased by 10% at 85% stress level in 90° compression direction. The alteration in loading direction modifies the included angle corresponding to the stress component. The stress component parallel to the fiber direction under compressive fatigue load leads to interfacial debonding in the composites, whereas the stress component perpendicular to the fiber direction results in pronounced shear failure.展开更多
Experiments were made on plain concrete subjected to triaxial static loading and constant amplitude compressive fatigue loading with a constant lateral pressure in two directions. The initial confining pressure was 0...Experiments were made on plain concrete subjected to triaxial static loading and constant amplitude compressive fatigue loading with a constant lateral pressure in two directions. The initial confining pressure was 0, 0.1 f c , 0.25 f c and 0.4 f c , respectively, for the static test, and 0.1 f c and 0.25 f c for the fatigue test. Based on the triaxial compressive constitutive behavior of concrete, the inflexion of confining pressure evolution was chosen to be the fatigue damage criterion during the test. The rule of evolution of longitudinal maximum and minimum strains, longitudinal cyclic modulus and damage were recorded and analyzed. According to the Fardis Chen criterion model and the concept of equivalent fatigue life and equivalent stress level, a unified S N curve for multi axial compressive fatigue loading was proposed. Thus, the fatigue strength factors for different fatigue loading cases can be obtained. The present investigation provides information for the fatigue design of concrete structures.展开更多
基金supported by the National Natural Science Foundation,China(Nos.52073224,12472141 and 12002248)the Natural Science Foundation of Shaanxi Province,China(Nos.2023KXJ-034 and 2023KXJ-005)+3 种基金Xi’an Science and Technology Plan Project,China(No.2022JH-ZCZC-0004)the Young Talent Fund of University Association for Science and Technology in Shaanxi,China(No.20210509)the Scientific Research Project of Shaanxi Provincial Education Department,China(No.22JC035)Shaanxi Outstanding Youth Science Fund Project,China(No.2024JC-JCQN-03).
文摘This paper reports the effects of fiber breakage defects and waviness defects on the compressive fatigue behavior and the progressive damage evolution process of 3D Multiaxial Braided Composites (3DMBCs). Combined with finite element compression simulation and ultra-depth microscope, the internal defect content of composites with different braiding angles was determined. The results demonstrate that the weakening effect of waviness and fiber breakage defects is greater than the strengthening effect of the braiding angle. This causes the fatigue resistance of 3DMBCs with the 31° braiding angle being better in both directions of 0° and 90°. The increase of 4° waviness and 10% fiber breakage defect results in the average fatigue life of composites being shortened by 48% and the energy consumption rate increased by 10% at 85% stress level in 90° compression direction. The alteration in loading direction modifies the included angle corresponding to the stress component. The stress component parallel to the fiber direction under compressive fatigue load leads to interfacial debonding in the composites, whereas the stress component perpendicular to the fiber direction results in pronounced shear failure.
文摘Experiments were made on plain concrete subjected to triaxial static loading and constant amplitude compressive fatigue loading with a constant lateral pressure in two directions. The initial confining pressure was 0, 0.1 f c , 0.25 f c and 0.4 f c , respectively, for the static test, and 0.1 f c and 0.25 f c for the fatigue test. Based on the triaxial compressive constitutive behavior of concrete, the inflexion of confining pressure evolution was chosen to be the fatigue damage criterion during the test. The rule of evolution of longitudinal maximum and minimum strains, longitudinal cyclic modulus and damage were recorded and analyzed. According to the Fardis Chen criterion model and the concept of equivalent fatigue life and equivalent stress level, a unified S N curve for multi axial compressive fatigue loading was proposed. Thus, the fatigue strength factors for different fatigue loading cases can be obtained. The present investigation provides information for the fatigue design of concrete structures.
