Advanced Materials Research Vols. 891-892

Abstract: For the purpose of clarifying the fatigue strength of a main girder web connected to a lateral girder flange which is repaired by bolting-stop-hole method with attached steel plates, fatigue tests have been performed on girder specimens. In addition, fatigue tests have been also carried out on small scale plate specimens modeling the repaired parts in order to investigate the fatigue crack origin and fatigue strength of the repaired parts. Furthermore, the effect of the repair method has been compared with those of stop-hole method and/or bolting-stop-hole method through the fatigue tests. It has been confirmed that the fatigue strength of the repaired parts is considerably high and almost equal to that of friction type of high strength bolted connections.

Abstract: The puddled iron is known for its extended use in monumental construction during the second half of the nineteenth century; among the structures built with such material are about half of French railway metallic bridges, most of them with over a century of service life. This scenario rises several concerns about the resistance of this material to cyclic loadings and therefore its fatigue behaviour. However, the puddled iron possesses several properties that make its mechanical characterization particularly difficult. Due to the puddling process this metal contains an important number of non-metallic inclusions that not only will turn out in a heterogeneous material but also (due to the rolling process) into an anisotropic one. In this paper a fast characterization of fatigue properties is proposed by using the self-heating method. The experimental self-heating curves obtained from specimens of the bridge of Toles (Chaumont, France) showed a scatter that was not observed in homogeneous materials (modern steel for example), this phenomenon is explained by the lack of determination of the representative elementary volume of the puddled iron. However, this data gives us important information such as the minimum and maximum boundaries of the mean fatigue limit for several orientations. An anisotropic two-scale probabilistic model for high cycle fatigue is also used to represent the orientation dependency of the results and the scatter found on the experimental data by using Hills elasto-plastic law and Weibulls distribution law to describe several characteristics of each site where the microplasticity occurs. The influence of such parameters and the limitations of the model are also discussed.

Abstract: This study investigated the effects of fatigue loading and corrosive environment on bonding strength and failure modes of Carbon Fibre Reinforced Polymer (CFRP)-laminated steel. A series of tests on CFRP bonded steel plate joints was conducted. The joints were immersed in the temperature controlled sea-water with a preload. After immersions for one and six months, they were subjected to cyclic loading for a pre-set number of cycles, and then tensioned to failure. The effect of fatigue loading alone was studied by the authors in the past. In the present study, the results of the cyclic and static loading tests were compared. The comparisons between the current and previous results have provided data on the durability of CFRP/steel joints under this environmental condition.

Abstract: Fatigue cracking reported in a lighting pole on an elevated bridge structure near Wellington raised the question of how to better design for and predict the fatigue life of lighting poles subject to wind induced fatigue. There have been concerns as to the reliability and currency of the methods commonly used in New Zealand. The paper therefore reviews current international design methods and describes the development of an improved fatigue design method for lighting poles in New Zealand. The new method uses fracture mechanics based crack growth formulations in conjunction with a modified J.D. Holmes Method for wind response analysis of the pole to varying wind speeds. Cumulative crack growth is calculated iteratively rather than using an S-N curve based Palmegran-Miner summation. Wind spectra used in the method are developed from long term meteorological records at representative locations. Software has been prepared to enable quick assessment of the expected fatigue life of lighting poles, and associated gear openings and holding down bolts The method and software has been calibrated with reference to full scale laboratory fatigue proof testing of representative base stubs and natural wind response testing of a 12 m high lighting pole.

Abstract: There is a great potential in using fibre reinforced polymer (FRP) to strengthen aging metallic structures. This paper briefly describes the benefit of using FRP to strengthen metallic structures. It then addresses how fatigue load affects the bond between FRP and steel. FRP fatigue strengthening of cracked steel plates and connections are discussed. Furthermore, effects of using prestressed FRP on flexural and fatigue behaviours of a FRP-steel composite system are addressed. Bonded and un-bonded FRP-to-steel applications, as two different approaches for steel strengthening, are discussed. Finally fatigue strengthening of metallic riveted bridges using un-bonded pre-stressed FRP plates is presented. A comprehensive list of references is provided.

Abstract: This paper investigates the possibility of determining damage under fatigue loading in carbon fibre reinforced plastics (CFRP) by using mechanical stiffness. Therefore, stress-strain-hysteresis recorded in fatigue tests under sinusoidal loads are used for moduli calculation. Additionally, a new method for stiffness evaluation called cyclic tensile tests is presented. Its results are compared to results from hysteresis analysis and to actual damage mechanisms monitored non-destructively with thermography analysis.

Abstract: Delamination or crack propagation between plies is a critical issue for structural composites. In viewing this issue and the large application of woven fabrics in structural applications, especially the ones that requires high drapeability to be preformed in a RTM mold cavity such as the asymmetric ones, e.g HS series, this research aimed in dynamically testing the carbon fiber 5HS/RTM6 epoxy composites under opening mode using DCB set up in order to investigate the crack growth rate behavior in an irregular surface produced by the fabric waviness. The evaluation of the energy involved in each crack increment was based on the Irwin-Kies equation using compliance beam theory. The tests were conducted at constant stress ratio of R=0.1 with displacement control, frequency of 10 Hz, in accordance to ASTM E647-00 for measurement of crack growth rate. The results showed large scatter when compared to unidirectional carbon fiber composites due to damage accumulation at the fill tows.

Abstract: The residual strengths of laminated composites containing notches or holes depend on the characteristic dimension of the notches as well as the laminate properties. This paper presents an experimental and computational investigation of the effect of orthotropy as well as scarf notch angles on the compressive strength of composite laminates made of seven different stacking sequences with the number of plies ranging between 20 and 24. Specimens containing scarfed holes of different scarf angles (6° and 10°) and straight holes of two different diameters (3.175mm and 6.35mm) were tested for comparison. Experimental results of the compressive strengths, normalised by the respective un-notched compressive strength show that the extent of orthotropy, defined as the laminate stiffness ratio along and perpendicular to the main loading direction, has a major effect. Computational modelling was carried out using the finite element method to quantify the residual strength; in which ply fracture is modelled using the continuum damage mechanics approach.

Abstract: Most engineering components and structures contain stress concentrations, such as notches. The state of stress at such concentrations is typically multiaxial due to the notch geometry, and/or multiaxiality of the loading. Significant portions of the fatigue life of notched members are usually spent in crack initiation (crack formation and microscopic growth) and macroscopic crack growth. Synergistic complexity of combined stress and stress concentration has been evaluated in a limited number of studies. Available experimental evidence suggests the current life estimation and fatigue damage analysis techniques commonly used may not be capable of accurate predictions for such complex and yet highly practical conditions. This paper investigates notched fatigue behavior under multiaxial loads using aluminum alloys. Many effects involved in such loading conditions are included. These include the effects of stress state (axial, torsion, combined axial-torsion), geometry condition (smooth versus notched), and damage evolution stage (nucleation and micro-crack growth versus long crack growth).

Abstract: The certification of scarf repairs requires that the repair is capable of handling flight loads in the presence of disbonds. This paper presents a study of the fatigue disbond growth behaviour of scarf joints. By determining the strain energy release rates of a disbond in a scarf joint subjected to a unit load, a predictive model based on linear elastic fracture mechanics is presented, which is shown to correlate well with experimental results. This method offers a promising technique of predicting the fatigue life of composite scarf joints with disbonds.