Narrow Results

The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler's headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. In this study, a T type welded joint of SS400 was adopted for the header of small-sized single pass boilers. Fatigue testing and FEA was carried out. The fatigue limit was greater for base metal than for weldment. For the weldment, the S-N curve decreased with decreasing ρ value. The stress concentration at the toe was evaluated by the FEA. S-N curves for different toe curvature radii were re-drawn using maximum elastic stress, Ktσmax. Crack initiation occurred in the vicinity of the toe. Several small cracks were observed on the surface of T type welded joint fatigue specimen at N/N_f=0.42. These cracks coalesced together at a crack length of 10mm. Fatigue crack growth rate lineally increased with increasing (crack length)^1/2.

We compared the fatigue characteristics of weld metal with those of base metal heat-treated and non heat-treated. Also, we examined the influence of bead on fatigue life. From the experimental results of this study, it has been seen that the fatigue characteristics of welded specimens grinded the toe of bead are slightly better than those of welded specimens not grinded. Fatigue life is affected more by the stress concentration due to the profile change in the weld toe rather than by the residual stress, and heat-treatment had almost no influence on the fatigue characteristics.

The fatigue behavior of welded thin-walled T-joints made up of both circular hollow section (CHS) braces and chords, subjected to cyclic in-plane bending, is described in this paper. CHS chords and braces are of thicknesses less than 4 mm. Current fatigue design guidelines show that the design of welded tubular nodal joints is restricted to thicknesses greater than or equal to 4 mm. The increased availability and use of thin-walled (t<4 mm) tubes of high-strength steels in recent years, in structures subjected to cyclic loading, means that it is important to study the fatigue behavior of welded thin-walled tubular nodal joints. In this paper, welded thin-walled CHS-CHS T-joints subjected to constant-stress-amplitude cyclic in-plane bending range are studied. The stress concentration factors (SCFs) determined experimentally at the brace and chord crown positions are shown to be about 30% and 40% respectively of the SCFs determined using parametric equations in existing fatigue design guidelines. The fatigue tests showed that in welded thin-walled CHS-CHS T-joints, a through-thickness crack occurs when the surface crack length along the weld toes in the chord has grown to a length equal to about 40% of the circumference of the brace member. An end of test failure criterion was proposed as an alternative to the through-thickness failure criterion, in obtaining data that is suitable for determining fatigue design S-N curves.

To predict strength of a composite loaded arbitrarily using its constituent information, in situ strengths of the matrix, different from its original counterparts, must be provided. Experiments can measure only the original strengths. Nobody is practically able to measure an in situ one. In our previous work, a stress concentration was found to be the main reason causing the difference between the in situ and the original strengths. In this study, we point out that the previous evaluation on the stress concentration factor (SCF) is valid only in the case of a transverse tension. When a unidirectional (UD) composite is subjected to a transverse compression, its failure surface has an inclined angle to the loading direction and a different SCF from that under a transverse tension is resulted. Explicit derivation of the SCF under a transverse compression is presented in this work. The matrix in situ transverse tensile and compressive strengths are assigned as its original counterparts divided by the respective SCFs. These in situ strengths together with the other original constituent properties are used as input data for strength prediction of a number of UD composites. Favorable correlation between the theoretical and experimental data has been shown.

Stress concentration factors (SCFs) in finite width plates with both elliptical opening and elliptical fillings under uniaxial loads are predicted. ANSYS Parametric Design Language (APDL) is applied to build the finite element models for the plates and to perform the analysis. The influences of geometric and material parameters such as the lengths along macro-axis and minor axis of opening, the eccentricity position of the opening, and the elastic modulus of the fillings on SCFs are discussed. The results show that SCFs in the finite width plate with elliptical opening can be significantly improved by substituting the opening with hard filling, and hard filling with high elastic modulus is effective to support the maximum stress in the plate, and the results are in good agreement with those from theoretical prediction. The present study may provide designers with an efficient way to estimate the filling effect on finite width plate structures with openings.

The purpose of this paper is to investigate the influence of cohesive zone model (CZM) on the mechanical properties of CNTs-composites with debonding interface, and the finite element computation is carried out by the ANSYS software with CZM. The CZM model represents the interface separation and traction using three parameters derived from a surface potential function, and the effective plastic strain and stress concentration factor are calculated for the models with and without cohesive zone. It is obviously found that the effective plastic strain increases and the stress concentration factor decreases with the application of CZM, and it is reasonable to improve the mechanical properties of CNT-composites with debonding interface by applying the CZM.