Papers by Keyword: Damage Mode

Abstract: In this paper, three kinds of different fiber reinforced vinyl composite plates are prepared by VARI technique, the mechanical parameters and failure modes of these panels under different strain rates are experimentally studied. The results show that loading velocity has a great influence on the tensile modulus of elasticity and strength as well as failure mode of the plates. At the same time, UMAT functional element program is used to write the failure criterion by ABAQUS finite element software, then the damage mode of composite fiber and matrix under tensile load are studied.

Abstract: Composite overwrap systems have been widely used to repair damaged pipelines. Its effectiveness has been proven by many researches and engineering applications. However, the research on progressive failure mode of the repaired structure has not been reported. In the present paper, finite element method with Hashin failure criteria is developed to realize the progressive failure analysis. The predicted burst pressure is in good agreement with the burst experiment. Different from widely-reported failure progress in Composite Overwrapped Pressure Vessels (COPV), the progressive failure analysis for the defected pipeline overwrapped by composite reveals very different failure stages: stable failure propagation and rapid failure propagation. The identification of critical pressure between these two stages is valuable in composite reparation design for the defected pipeline.

Abstract: This study applies the nonlinear finite element analysis software LS-DYNA to conduct a numerical simulation of damage mode of reinforced concrete slab under complex boundary condition subjected to air blast load. The factors affecting damage model of reinforced concrete slab, standoff distance and explosives location, were analyzed. The results show that: With the increase of the standoff distance, the failure mode of RC slab gradually changes from localized punching failure to shear failure at the support. With the location for explosive changing from the center of RC slab to the beam plate combination, the failure mode of RC slabs gradually changes from localized punching failure to bending-shear failure under close-in blast loading.

Abstract: Corrosion fatigue (CF) of aluminum alloy is an important form of aircraft structural damage. Considering the real service conditions, it is necessary to study the effects of the coating on the CF process. The CF lifetime tests were conducted in 3.5% NaCl solution. The coating could well protect specimens before it damaged and markedly improved the resistibility of CF. According to results of S-N fatigue curves, at σ_max=250MPa, real-time detection of the CF process for LY12CZ aluminum alloy with and without coating was performed using digital acoustic emission (AE) technique. Three damage modes, namely, coating damage, corrosion and crack propagation, were determined using AE parameters analysis, that is the distribution of amplitude and peak frequency.

Abstract: Thermoplastic self-reinforced polyethylene (PE/PE) composites were tested under quasi-static tensile load and the failure processes weremonitored by Acoustic Emission (AE) technique. The AE signals were collected and clustered by Unsupervised Pattern Recognition (UPR) scheme. The initiation and progression of the damage mechanisms in the composites can then be reviewed by the cumulative AE hits of each cluster versus strain curves. But the labeling of each cluster is crucial to the failure analysis. The paper focuses on this correlating between the obtained clusters and their specific damage modes. This was carried out by waveform visualization and Fast Fourier Transform analysis. Pure resin and fiber bundles were tested to assist in the labeling of signal classes in the composites (90°, 0° and [±45°] specimens). Typical waveforms of matrix cracking, fiber-matrix debonding, fiber fracture and fiber pullout were indentified respectively. The evolution process of various damage mechanisms in the composites revealed that the correlating method was effective. An objective and repeatable analytical procedure is established for the investigation of progressive failure mechanisms in the thermoplastic composites.

Abstract: In the present paper, FE model of the single-layer Kiewitt-8 reticulated domes with a span of 60m was built with using of ANSYS/AUTODYN. The dynamic response of the reticulated domes against the multi-point impact was investigated, where a special impactor was involved. Based on the simulation results, four damage modes were concluded，which are local damage, global collapse, local damage with punching plug, punching plug respectively. It was indicated that the initial kinetic energy of the impactor have a close correlation with the damage mode. Furthermore, the characteristics of dynamic response for each damage mode were shown.

Abstract: More and more advanced composite materials are used in mainly supporting structure of civil aviation; its airworthiness safety should be the focus of the research. Damage assessment is the key step in the general composite repair procedure. In this paper, the ANSYS calculating method is validated on the basis of classic laminate theory which could be used to calculate composite strength. In one case, it is applied to simulation and modeling of the B767 landing gear door. The case shows that composite damage mode such as low velocity impact damage, curing and fatigue could be evaluated with finite element method, the result of evaluation is provided as a means to composite damage assessment. Thereafter, the finite element method can be used for structural health monitoring to advanced composites.

Abstract: In this paper, the concept of system capacity is expounded from the perspective of the system theory. The selection of control index during the aseismatic design of frame infill wall structure is discussed, and the critical techniques of the system capacity method are proposed. Finally, the process of the aseismatic design method based on system capacity is developed.

Abstract: An experimental study of low velocity impact (LVI) was carried out on 2D carbon fabric reinforced silicon carbide (C/SiC) ceramic matrix composites. The C/SiC composite specimens were impacted by using a free-drop impact machine at different energy levels ranging from 1J to 9J and acoustic emission (AE) technique was used to detect the damage process. The results indicated that AE signals could evaluate the LVI damage behaviors of C/SiC composites from the different aspects. By comparing impact load process with AE hits and AE amplitude, the damage process could be determined. In the loading stage, matrix cracking mainly occurred in the composites; when impact load reached peak load, delamination and fiber fracture started to produce; in the unloading stage, the damage modes were mainly delamination and matrix cracking. AE event count fractions could quantify the main damage modes at different impact energy levels. At lower impact energy, matrix cracking was the main damage mode; when impact energy were between 3J and 6J, delamination and matrix cracking became the main damage modes; at higher impact energy, fiber fracture was the main damage mode.

Abstract: Quasi-static indentation (QSI) tests on plain weave carbon fiber reinforced silicon carbide (C/SiC) ceramic matrix composites (CMC) have been performed to study the damage evolution law and damage modes. Acoustic emission (AE) and Ultrasonic C-scan techniques are creatively used to monitor the damage process and detect the indented damage, respectively. The damage development process could be described by three evidently different stages: initial crack tips spreading along within the matrix, matrix cracking and delamination as well as fiber bundles breakage of different layers. The AE activity indicated that the main damage modes are matrix cracking and delamination in the first two stages, once the pressing force exceeds the peak load the damage mode will change into fiber bundles breakage. Moreover, the damage procured in the QSI test is slightly lower than that produced in the low velocity impact (LVI) test under the equivalent energy, the correspondence between the two test methods is reasonably good.