Fracture and Damage Mechanics V

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Authors: Kil Sung Lee, Kwang Hee Im, In Young Yang
Abstract: The purpose of this study was to develop lightweight hat shaped section side members which absorb the most of the energy during the front-end collision of vehicle. The hybrid side member was manufactured by combination of aluminum and CFRP. An aluminum or CFRP (Carbon Fiber Reinforced Plastics) member is representative lightweight materials but its axial collapse mechanism is different from each other. The aluminum member absorbs energy by stable plastic deformation, while the CFRP member absorbs energy by unstable brittle failure with higher specific strength and stiffness than those in the aluminum member. Based on the respective collapse characteristics of CFRP side and aluminum members, the hybrid side members were tested on the axial collapse loads to get a synergy effect when the member is combined with the advantages of each members, such as energy absorption by the stable folding deformation of the aluminum member and by the high specific strength and stiffness of the CFRP member. Energy absorption capability and collapse mode of the hybrid side members were analyzed.
Authors: Jin Woo Kim, Dong Gi Lee
Abstract: While mold fiber reinforced composite material to problem of occasion that high temperature compression molding, flow length in mold is overlong or when flow meets with resistance in side of mold, fiber orientation happens and big change occurs in strength or quality. Thus, in compression molding that use fiber reinforced composite material, orientation state of fiber in moldings is the most basic element that quotes various properties of matter values. Therefore, to clear orientation state of fiber establishing measurement of fiber orientation angle distribution is very important while give correction of molding condition decision, mechanical quality of moldings and guide about material design. In the study, the fiber orientation distribution of simulation figure plotted by PC is measured using image processing in order to examine the accuracy of intersection counting method. The fiber orientation function measured by intersection counting method using image processing is compared with the calculated fiber orientation function. The results show that the measured value of fiber orientation function using intersection counting method is lower than the calculated value, because the number of intersection between the scanning line and the fiber with smaller fiber aspect ratio is counted less than with larger fiber aspect ratio.
Authors: In Young Yang, Uk Heo, Kil Sung Lee, Je Woong Park, Young Sub Kweon, David K. Hsu, Young Tae Cho, Chong Ho Lee, Kwang Hee Im
Abstract: Since layup orientation of the laminates greatly influences its properties, an NDE technique for layup orientation determination would be very beneficial. It is desirable to perform contact-less nondestructive evaluation to assess material properties and defects of composites because of permeation of coupling medium such as water. An ultrasonic technique would be very useful, which could be used to test the part after and before curing laminates and requires less time than the optical test. First of all, conventional ultrasonic experimentations were conducted using water as a transmitting medium. In contrast, air-coupled ultrasound is non-contact and has clear advantages over water-coupled testing. Therefore ultrasonic systems for air-coupled and conventional ultrasound were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of orthotropic composite laminates. With the transmitter and receiver on the same side of a laminates, Lamb waves were generated and used for the amplitude magnitude. As a result, it was confirmed that the influence of fiber direction in the laminates could be detected by the non-contacting or contacting inspection from one-side and the detectability was improved by using shaped tube for reducing the specular reflection on transmitting. Furthermore, a vector decomposition model was utilized for lay-up error of the orthotropic laminates. Finally, aircoupled results well corresponded somewhat to those of contact ultrasonic examination in the orthotropic laminates.
Authors: Juan Xia Zhang, Chun An Tang, Xing Jie Hui, Wan Cheng Zhu, Zheng Zhao Liang, Yong Bin Zhang, Xian Zhang Guo
Abstract: A numerical code RFPA3D (Realistic Failure Process Analysis) is used to simulate the crack initiation and propagation in FRP-strengthened concrete beam under external loading. In our model, the FRP-strengthened concrete is assumed to be a three-phase composite composed of concrete, FRP, and interface between them. The displacement-controlled loading scheme is used to simulate the complete failure process of FRP-strengthened concrete the numerical simulation of failure process of the specimens. It is found that the main failure mode is the interfacial debonding and the interfacial debonding may propagate either within the adhesive layer or through concrete layer in the vicinity of bond interface. The simulation results agree well with the experiment observations. The width of the FRP sheet is considered an important factor not only to significantly influence the debonding propagation type and crack distribution but also to control the ultimate load-capacity and ultimate strain. This study is focused on the failure process of the FRP-strengthened concrete beam and the effects of the width of FRP sheet on the failure mode and on the structural load-carrying capacity of concrete structures.
Authors: Xi Lan Feng, Zhi Qiang Jiang, Jin Fa Shi
Abstract: The effects of roll materials, mould parameter, pouring parameter and cooling parameter on the crack of high speed steel (HSS) roll fabricated by a centrifugal casting have been analyzed. The modification of HSS roll was researched. The structures and properties of HSS roll modified by potassium and rare earth were improved. The hot tearing force of modified HSS roll increased by 32.77% and reached 158N. Modification was able to decrease the line constriction. The adoption of variable speed centrifugal casting technique, variable flux pouring technique and variable speed solidification cooling technique was able to adjust the temperature field and stress field of the roll, which benefited the filling and solidification of molten steel and eliminated the crack of HSS roll.
Authors: Qing Bin Cui, Jing Zhu Zhang, Guan Hai Xue, Shi Chun Chen, Lei Lei
Abstract: Dynamic analysis, finite element analysis and fatigue life analysis of transmission gear of Self-Propelled Gun is achieved in this paper according to the theory of multi-body dynamics, finite element and cumulative fatigue damage, and the well-known software Pro/E, ADAMS, PATRAN and FE-Fatigue are integrated in the research. The virtual prototyping model of self-propelled gun’s transmission box is built by ADAMS software. The dynamic load spectrum of transmission gear is achieved by virtual driving of Self-Propelled Gun. The finite element model of the gear is built by using PATRAN software, after defining reasonable boundary conditions, material and element properties, according to the load and the fatigue failure criterion of the gear, the stress-strain state of gear on load is studied. The dynamic load spectrum and the stress-strain state of the gear are considered as basic input data, the fatigue life of the gear is calculated by using FE-fatigue software. The road haul of gear without fault is predicted when the self-propelled gun drives on the second-class load surface at low speed. This method offers a new idea to the fatigue life prediction. It can predict fatigue life without experiments, and save cost and time. It has the great significance to the optimization design of the self-propelled gun.
Authors: Chun Sheng Wang, Jian Guo Nie, Ai Rong Chen, Wei Zhen Chen, Yue Xu
Abstract: There are many old steel bridges on Chinese transportation lines, which keep their normal traffic service function. The old bridges are often required to carry an increasing volume of traffic and heavier vehicles than the original design, so bridge management departments pay more attention to the actual remaining fatigue life of such structures. Based on probabilistic fracture mechanics theory, the member and the system fatigue failure evaluation models for old steel bridges are all proposed, and the fatigue reliability analysis program is developed using Monte-Carlo. As a case study, the evaluation models are used to predicate the fatigue reliability of Zhejiang Street Bridge. According to evaluation results, the probabilistic remaining fatigue life, safe inspection intervals and maintenance strategy are determined.
Authors: Gang Yang, Ai Feng Zhang, Wei Ping Hu, Bao Zong Huang
Abstract: This paper proposes an improved damage model and derives the shear correction factors for the model based on the Whitney[1] method. As the model is mainly used in the delamination front, the overly strong assumptions for geometric deformation in this region may be relaxed so that more realistic displacement fields can be established.
Authors: Lian Chong Li, Chun An Tang, P.A. Lindqvist
Abstract: Using RFPA code, analyses have been carried out to investigate the stability of a rock pillar in a experiment for nuclear waste repositories, the numerically obtained stress field, temperature distribution, failure pattern of the pillar rock and associated AE events are all agree well with the in-situ data. Minor fracture initiation may take place in the vicinity of the boreholes after heating. Heating induces minor spalling at central pillar wall for 0.5 m sections below the tunnel floor, but the area of spalling is found to be limited. The core of the pillar remains intact for stress conditions corresponding to 120 days of heating which not only prove that the proposed technique provides a powerfully alternative and effective approach for the study on thermal-mechanical-damage coupling mechanism but also provide meaningful guides for the experiment design and associated applications.
Authors: Shi Cheng Liu, Shi Yong Liu, De Yi Liu
Abstract: Fracture surface and crack propagation in low temperature brittle fracture (LTBF) of an 18Cr-18Mn-0.7N high nitrogen austenitic steel (HNAS) were examined by means of scanning electronic microscopy, and compared with behaviours of LTBF of low carbon steel. Similar to BCC low carbon steel, the HNAS experienced a typical ductile-to-brittle transition (DBT) with decreasing temperature, and the appearance of the fracture surface transited from fibrous to granular. Dual-surface observation revealed that there were three types of fracture modes in LTBF of the HNAS: annealing twin boundary fracture, intergranular fracture, and transgranular fracture. The annealing twin boundary fracture facets were parallel to {111} planes, and were fairly flat and smooth, with a pattern of three sets of parallel straight-lines intersecting at 60. There were also bent steps that originated and terminated at grain boundaries. The transgranular fracture facets were coarse and uneven, with uniformly distributed small pits and partially river pattern on them. The intergranular fracture facets were smoothly curved ones on which more than three sets of parallel deformation structure trace lines were observed. Careful observation on crack propagation demonstrated that during LTBF of the HNAS, microcracks formed firstly at grain boundary and annealing twin boundary, and then these microcracks came together and coalesced to induce crack propagation through grains, resulting in a fracture appearance with shiny facets distributing in dull facets.

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