Key Engineering Materials Vols. 385-387

Abstract: This paper primarily describes the development and application of substructure computational analysis techniques in two-step hirarchical strategy to determine stress intensity factors for the stiffened damaged panels subjected to fatigue internal pressure. A program based on substructure analysis technique and global-local hierarchical strategy has been developed for the fracture analysis of curved aircraft panels containing cracks. This program may create superelements in global and local models, and obtain fracture parameter of the crack in local model by expanding results in superelements automatically. The technique is applied to the analysis of a cracked panel with 7 frames and 10 stringers. SIFs of four cracks in it with different crack lengths are obtained efficiently.

Abstract: A muffler is an important part used to reduce noise and to purify exhaust gas in cars and heavy equipments. Recently there has been a growing interest in the designing and manufacturing the muffler tube due to the strict environmental regulations. The technique of perforating on the muffler tube has been largely affected by the shear clearance. And considering the concentration of the force around the punch edge, it is essential to reduced it through the punch radius. In this research, finite element analysis has been carried out to predict optimal forming conditions of the muffler tube using DEFORMTM-3D. In analysis, using one-fourth component of the punch and die, metal forming process is simulated and Cockcroft-Latham ductile fracture theory is used. According to the simulation results, when the shear clearance is 0.04mm, the punch radius is 0.05mm and the value of plate holder force is 250KN, the relation of load-stroke for punch is optimized. Also the burr is minimized and optimal shear section is obtained. The simulation results are reflected to the forming process design for the muffler tube.

Abstract: This paper proposes a life-cycle cost (LCC) management methodology that integrates corrosion deterioration and fatigue damage mechanisms. This LCC management methodology has four characterized features: (1) corrosion deterioration and fatigue damage models are used to predict the time when the pre-defined limits are reached; (2) the performance of the steel girder is measured by condition state sets in which deflection, moment and shear capacities and fatigue strength limits are considered altogether; (3) the cost-effectiveness of management strategies are measured by the performance improvement per unit of money spent; and (4) the LCC model includes initial design/construction cost, inspection cost, maintenance cost, repair/rehabilitation cost and failure cost. A steel girder bridge is used as an example to demonstrate the application of the proposed LCC management methodology.

Abstract: Al-Li alloys are characterized by a strong anisotropy in mechanical properties and microstructure with respect to the rolling direction. Plates of 2198 Al-Li alloy were friction stir welded by employing maximum rotation speed: 1000 rev/min and welding speed of 80 mm/min, both in parallel and orthogonal directions with respect to the rolling one. The joints mechanical properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests performed with a resonant electro-mechanical testing machine under constant amplitude control up to 250 Hz loading, were conducted in axial control mode with R(σmin/σmax)=0.33, for all the welding and rotating speed conditions. The fatigue crack propagation experiments were performed by employing single edge notched specimens.With the aim to characterize the weld performances, both the microstructure evolution at jointed cross sections, related to the welding variables, and the fractured surfaces were respectively analyzed by means of optical and scanning electron microscopy.

Abstract: Founded on the energy storing characteristics of microstructure during irreversible deformation, a viscoplastic constitutive model with no yielding surface introduced was developed for single crystals by adopting a spring-dashpot mechanical system. Both plastic dashpots reflecting the material time-independent responses and Newtonian dashpots mirroring the material time-dependent viscous responses were introduced to describe the viscoplasticity of slip systems. The single crystal constitutive model was established based on the thermodynamics of internal variables and the theory of absolute reaction rate. By implementing the KBW self-consistent theory, a polycrystal viscoplastic constitutive model was formed. The numerical analysis in corresponding algorithm was significantly simplified as no searching process for the activation of the slip systems and slip directions was required. The numerical simulation of creep-plasticity behaviors demonstrated excellent agreement with the corresponding experimental data.

Abstract: This research is an experimental study on full-scale interior slab-column connections of flat-plate. Three types of shear reinforcements were proposed to prevent brittle punching shear failure that could result in collapse of whole flat plate structures. A series of four flat plate specimens including a specimen without shear reinforcement and three specimens with the reinforcements was tested. The dimension of the slabs was 2620*2725*180mm and the specimens had a 600*800mm square column at the center of the slabs. The slabs were tested up to failure using monotonic vertical shear forces. The presences of the shear reinforcements substantially increased punching shear capacity and ductility of the interior slab-column connections.

Abstract: A series of five shear wall specimens were tested under constant axial stress and reversed lateral cyclic loading in order to evaluate the seismic retrofit methods that had been proposed for shear walls with new openings. The test results showed that the failed specimens had shear fractures and two different retrofit methods had different effects on the strengths of each specimen.

Abstract: The purpose of this research was to study the response of slab-column connections containing various types of shear reinforcement when subjected to the combination of gravitational and lateral cyclic loads. The three test specimens were full-scale representations of exterior slabcolumn connections of a prototype apartment building in Korea. The control specimen had no shear reinforcements, while the other specimens had CS-Bar and SS-Bar as shear reinforcements. The control specimen failed due to the punching shear around the slab-column connection at 4.0% drift. None of the specimens with shear reinforcement experienced punching shear failure up to 4.4% drift. The two types of slab shear reinforcements proved to be equally effective in resisting punching shear failure of these connections subjected to relatively low levels of gravity load. The presence of shear reinforcements significantly increased the lateral load ductility of the connections. The test results showed that the strength and ductility of the specimens with SS-Bar and CS-Bar were improved by 23% and 15% compared to the specimen without shear reinforcements.

Abstract: A new strategy of finite differences method is proposed for analysis of notched cross-section bars under elastic-plastic torsion. Relation curves of the elastic-plastic torque responding with different positions, angles and lengths of the notches in one section are obtained by numerical tests. It can be seen that these relation curves exhibit obvious nonlinearity. Meanwhile, the stress intensity factors can also be easily calculated by utilizing the results of above finite differences method. It provides an effective way for solving such elastic-plastic fracture mechanics problem.

Abstract: The tensile properties of a titanium alloy reinforced with 3% by volume fraction of TiC particles and of an unreinforced titanium alloy are studied over a range of strain rates from 0.0001s-1 to 1300s-1 using quasi-static material testing system (MTS810) and split Hopkinson tensile bar apparatus. The experimental results show that both the TiCp/Ti composite and its matrix alloy exhibit an obvious strain-rate hardening property. But the high strain-rate sensitivity of the TiCp/Ti composite is significantly higher than that of the matrix. The high strain-rate sensitivity of the TiCp/Ti composite is considered to be originated from the high dislocation accumulation rate during dynamic deformation and the constraint of TiC particles on the surrounding matrix, which dramatically enhances rate of the matrix. Finally, a phenomenological dynamic constitutive relation is established considering the composite is elastic-perfectly plastic material.