Key Engineering Materials Vols. 306-308

Abstract: An experimental program has been conducted to study the perforation of stiffened steel plates by truncated oval-nose projectiles at normal impacts. The projectiles of 104mm diameter were fired at 921A stiffened plates with thickness 15.mm for the base plate at an initial velocity from 560m/s to 620m/s. High speed camera system was employed to record the perforation process and from the digital images, impact angles and projectile velocities during perforation were determined using image processing. Numerical simulations have been performed for projectiles against single and layered plates adopted in the experiments. The perforation process is explored in details and the deformation modes are obtained. By adopting an energy method, a four-stage analytical model that accurately predicts the residual velocity is developed. Simulation results, experimental data and theoretical predictions are reasonably well correlated.

Abstract: In this paper, we analyze a RVE of concrete reinforced (RC) with steel reinforcing bar in two vertical directions on basis of the thoughts of composite material and propose that in the ideal case the constitutive equation of reinforce concrete is declared to multiply the viscoelastic constitutive equation of concrete by a reinforcing multiplier G , which is depended on material characters and arrange mode of steel reinforcing bar. In the model, we draw the growing damage law on the assumption that damage only occur in the concrete. Subsequently, we obtain the damage viscoelastic constitutive equation of reinforced concrete. Lastly, the comparison with the plate impact test results of specimens shows that the proposed model can give consistent prediction of the dynamic behavior of SFRC.

Abstract: Impact energy and deceleration at a certain time are the most influenced factor to passenger’s safety when collision between railway vehicles occurred. In this paper, forced external inversion mechanism is considered as impact energy absorber. This mechanism is selected due to its constant inversion load along uniform tube [5] and the impact force is reduced because of its inertia effect [7]. Material used as energy absorber is mild steel. Numerical analysis using finite element method is utilized to study the energy absorption capacity and deceleration characteristic of tube external inversion mechanism for complex transient problem of collision. The real scale experimental study is used to validate the numerical analysis by crashing a moving vehicle to static train series where the impact energy absorber module using external inversion mechanism is attached in the tip of static train series. Characteristic that consider in numerical and experimental study are deformation and contact force. The deformation differences between numerical and experimental study are under 9%. Whereas for contact force, the experimental result of contact force disposed under 8% of numerical result for velocity of moving train at 10 and 15 km/h.

Abstract: This paper considers crash zone development for railway vehicle to improve it’s crashworthiness characteristics. The principle of modification is by weakening the crash zone area and strengthening the passenger area. Thus the huge impact energy during collision will be absorbed by crash zone area so that it will maintain the structural integrity of the passengers. There are two type of modifications proposed in this study. The first modification is conducted by weakening the end-under-frame section and strengthening the middle-under-frame section. These modification shows deformation characteristics improvement where the passenger area structure are not suffered from buckling and plastic deformation as expected. The second type of modification is full modification on end-under-frame. These modifications give better improvement on the deformation and energy absorption characteristics, however in the practical application, this will be more expensive option.

Abstract: A series of formulas about two-parameter parabolic Mohr strength criterion(2-PP Mohr criterion) are derived. Based on the results of uniaxial tension and uniaxial compression tests, the parameters involved in the criterion can be easily determined, then the criterion in terms of the major principal stress and the minor principal stress is derived, and the damage pattern is also discussed. At last, the formulas about the rupture angle and the friction angle are presented, and their relationship is also given. 2-PP Mohr criterion can describe not only shear but also tensile failure. In this criterion the ratio of the uniaxial compression strength and the uniaxial tension strength is not confined as in Griffith criterion. The formula about the rupture angle provides steady theoretical foundation for determining the direction of crack faces and damage patterns in the computation of macro crack propagation. In fact, Griffith criterion is only a special case of the two-parameter parabolic Mohr strength criterion proposed in this present paper.

Abstract: Reactor pressure vessel (RPV) is the most critical component in nuclear power plant. RPV is subjected to radiation embrittlement, which is characterized as neutron fluence-dependent reduction in fracture toughness of the material. Therefore, risk for potential failure of RPV increases as operating time and fluence level increase. To prevent the potential failure, it is requested for RPV to operate in accordance with pressure-temperature (P-T) limit curve during operation. However, it has been reported that P-T limit curve which is typically developed in accordance with the procedure in ASME code is too conservative. Therefore, in order to investigate the conservatism of current P-T limit curve and develop more realistic one, probabilistic approach based on the risk was utilized in this paper. The resulting P-T limit curve is very higher than that from deterministic approach, and can be used as alternative operation limit of the RPV, because probabilistic P-T limit curve seems to have enough safety margin for potential failure of RPV.

Abstract: The integrity of major components in nuclear power plant should be maintained during operation. In order to maintain the integrity of these components, complicated assessment procedures are required including fracture mechanics analysis, etc. The integrity assessment of components has been performed by using conventional deterministic approaches whilst there are lots of uncertainties to carry out a rational evaluation. In this respect, probabilistic integrity assessment is considered as an alternative method for nuclear component evaluation. The objectives of this paper are to develop an integrity assessment system based on probabilistic fracture mechanics and to estimate the failure probability of major nuclear components containing a defect. The integrity assessment system consists of three evaluation modules which are first order reliability method, second order reliability method and crude Monte Carlo simulation method. The developed system has been applied to evaluate failure probabilities of nuclear structural components such as steam generator tube and piping. The evaluation results showed a promising applicability of the probabilistic integrity assessment system.

Abstract: The connecting rod is one of the most important parts of an engine system. It fits in between the crosshead and the crankshaft and converts the piston’s reciprocating motion to rotary motion with the crankshaft. The connecting rod is subjected to a complex state of loading. High compressive loads and high tensile loads are due to combustion and connecting rod’s mass of inertia, respectively. This is why the connecting rod is the most stressed part of an engine system. If the engine is operating, connecting rod fails, this could cause a critical situation. Therefore, the connecting rod should be able to withstand tremendous load and transmit a great deal of power smoothly. In general, the failure occurs at the big end of connecting rod. Hence, the connecting rod’s big end corner radius was taken as a design variable. Also, three dimensional finite element analyses were performed. From these results, the stress distribution was estimated and the value of the corner radius was optimized.

Abstract: The behavior of piping elbows under bending and internal pressure is more complicated than expected. The main problem is that the coupling of bending and internal pressure is nonlinear; the resulting stress and displacement cannot be added according to the principle of superposition. In addition, internal pressure tends to act against the effect caused by the bending moment. If bending moment ovalise the elbow cross-section, with internal pressure acting against this deformation, then the ovalised cross section deform back to the original circular shape. It is then introduced the term “pressure reduction effect”, or in some literature, “pressure stiffening effect”. Current design piping code treats the pressure reduction effect equally for in-plane (closing and opening) moment and outof- plane moment. The aim of this paper is to present results of a detailed finite element analysis on the non-linear behavior of piping elbows of various geometric configurations subject to out-of-plane bending and internal pressure. Specifically the standard Rodabaugh & George nonlinear pressure reduction equations for in-plane closing moment are checked in a systematic study for out-of-plane moment against nonlinear finite element analysis. The results show that the pressure stiffening effects are markedly different for in-plane and out-of-plane bending.

Abstract: The fracture properties of Plexiglass bright the attentions of the researchers as it is the import material used in aero-planes industry The white speckle technique could obtain displacement fields nondestructively under the normal environment. Compare to the laser speckle method there are no interference light source and the vibration isolation needed. In the paper the principle of the technique is described and the displacement field near crack and SIF are measured. The results show that the technique is very suitable to the application in industry.