Key Engineering Materials Vols. 324-325

Abstract: An approximate analytical method is presented to analyze reliability for the structure with fuzzy-random uncertainty in basic variables. On the basis of equivalent transformation from fuzzy possibility distribution (FPD) to random probability distribution (RPD), this contribution expands first order and second moment method (FOSM) for random reliability to that for fuzzy-random reliability. The expanded FOSM is illustrated by the way of the fuzzy-random low fatigue life reliability analysis about an aeronautical engine disk affected by fuzzy-random uncertainty. Comparison between the FOSM and the numerical simulation for the fuzzy-random reliability demonstrates the precision of the presented computational model.

Abstract: Fatigue strength of duplex stainless steel welded joints with longitudinal fillet welded guess and with longitudinal flat side guess welded on plate was evaluated by hot spot stress, hot spot stress S-N curves were produced and compared with normal stress S-N curves. The results show that the hot spot stress fatigue strength of the two kinds welded joints should be expressed by only single S-N curve while nominal stress S-N curves can only be regressed respectively. The test data are greatly above the S-N curves with slope m=3, recommended by IIW, which indicates that the slope m=3(IIW) has great safety factor in practical engineering application. But there is no appreciable difference in fatigue strength between duplex stainless steel and common structural steel with similar welded joints when fixed the test data to slope m=3.

Abstract: The optimization design problem of vibration isolation and shock resistance system is studied in consideration of acoustical concealment performance and life-force of ships. The weakness of design method based on continuity is pointed out and combination optimal design method is brought forward. Then the limiting performance of shock isolation system is analyzed and two realization methods are discussed. One method is to adopt linear stiffness component with large damping. The other method is to use multiple linear stiffness components without damping. Simulation results showed that the optimal loss factor is still 0.4 when the stiffness of shock bumper is much larger than that of vibration isolator, just the same with that suffering from only shock loads. Simulation results also showed that limiting performance can be achieved by configuration optimal design using multiple linear components. The two discussed methods can be used to direct engineering application.

Abstract: For accurate determination of the service life we must take into account the loading, which are in most cases random loading of variable amplitude, the geometry and material properties of construction elements which are known not to be constants. The more precise these input parameters are modeled; the more precise and reliable are the results. In our paper we will deal in detail with the model of crack initiation and propagation in the complex structures as a basis of the algorithm for calculating the service life. For determination of the service life for the area of short cracks we used Bilby, Cottrell and Swinden model which is based on the theory of continuously distributed dislocations and we complemented it with random generation of structure of material before cracks. For the long crack we have developed a stochastic model for determination of service life.

Abstract: This paper presents a control and diagnostics model of single stage gear wheels using acoustic responses. The model is based on various methods and procedures that provide information about the generator’s condition and, specifically, its service life. Four procedures are combined in this model: the mathematical module of the gear wheel that translates the complete mechanical module into mathematical form, the adaptive FIR (Finite Impulse Response) filter that calculates impulse responses from the non-linear system, the module for calculating any impulse response, and the FFT (Fast Fourier Transform) frequency analysis used for simulating frequency spectrums. The result of the simulation is the sound frequency spectrum that allows the analysis of gear wheel tooth damage and, based on this spectrum, calculation of the remaining service life and/or the maintenance process.

Abstract: The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures since carbon fiber has good mechanical properties such as high tensile strength, good resistances to corrosion, and low self-weight, which are attractive for retrofitting of RC member. In using Carbon Fiber Mesh (CFM) as a retrofit material for RC member, most important structural property that should be developed is the bond strength between RC member and CFM. The additional strength increment by CFM can be developed if the bond strength is sufficient. If it is not, the strengthening effect can not be expected due to the bond failure between concrete and CFM. A direct tensile test was performed in order to find the variation of bond strength and load-displacement response of CFM attached to the concrete and the result is presented in this paper. The key parameters of the test are the location of clip for the installation of CFM, number of clips and thickness of cover mortar. Test results indicate that the bond strength is dependent on the number of clips and maximized at clip numbers of three per each rod. In specimens without clips, the highest strength was found in the specimen with cove mortar of 30mm and lowest one in specimen with largest mortar thickness. This means that in too much thick of cover mortar, it seems that the amount of drying shrinkage is increased and this reduces rather than improves the bond strength.

Abstract: A new theoretical concept of crack closure under plain strain was applied to assess the effective fatigue threshold under various loading condition for selected aluminium and titanium alloys of different microstructures. The concept is based on the long-range effect of geometrically necessary dislocations remaining in the wake of propagating fatigue cracks. Calculated threshold values FKeff,th for 7475 aluminium alloy are about 1.9 MPa.m1/2 (in vacuum) and 1 MPa.m1/2 (in air), and about 2.5 MPa.m1/2 and 3.3 MPa.m1/2 for c-titanium and Ti-2.5%Cu, respectively. All calculated values are nearly independent on both the microstructure and the applied stress ratio and they are in a good agreement with experimental data.

Abstract: In this paper, the continuous in-situ observations of the fatigue crack growth in U71Mn and U75V rail steel are made by using the scanning electronic microscope (SEM). The microstructure patterns of cracks under the mode I fatigue loads and quasi-static loads are presented. The results indicate that the short fatigue crack growth in rail steel is a quasi-cleavage fracture. The ductility and the performance of fatigue resistance of U71Mn rail steel are better than those of U75V rail steel.

Abstract: Fatigue crack initial life of multiple-site structure is described as the shortest life of all site’s fatigue initial lives. This paper will establish a method, which is described to estimate fatigue initial life of multiple-site structure. Using finite element method (FEM), the local stress concentration of each site is calculated. Using the statistical fatigue theory, the fatigue crack initial probability can be considered. Numerical example indicates: fatigue crack initial life of multiple-site structure is shorter then the life of single site. At the end of paper, experiment was executed adopting the same fatigue cycle loads with the computational case. The receivable relative error between the experimental result and the result of numerical analysis verifies the efficiency of this method.Introduction

Abstract: Many methods can be used to assemble large mechanical structures. Using rivets is one of these methods. Rivets are lighter than bolts and allows for efficient assembly. The cylindrical structure has a discontinuous rivet assembled region. So concentration load operates in the edge of discontinuous assembled region. This paper evaluates the force placed upon rivets used to assemble cylindrical structures and strength of structures assembled with rivets. Plastic deformation of rivets occurs at 4 kN and rivets are destroyed at 7 kN. However, rivets are designed to transfer load to neighboring rivets when they are overloaded. Structural test were accomplished using tension and bending load condition. The structural tests showed that plastic deformation first occurs in the fastening where the rivet meets the outside of the cylinder and a number of rivets exhibited this type of deformation. The secondary phase of deformation occurs in the fastening where the rivet meets the inside of the cylinder. Despite the plastic deformation, the structural tests showed that the rivets succeeded in redistributing load to neighboring rivets and as a result, no rivets were destroyed.