Paulo Pedro Kenedi

Influence of mechanical surface treatment on fatigue life of bonded joints

ABSTRACT Adhesively bonded joints can support a longer fatigue life if compared to conventional joining techniques, provided that a set of requirements is fulfilled. One of the most important requirements is the mechanical preparation of the bonded joint surface, which improves the joint interface adhesion. The aim of this work is to investigate the influence of surface roughness of mild steel substrates on fatigue behavior in adhesive bonded plates. To accomplish this objective, three different surface treatments were used on A36 steel substrate specimens, namely sand blasting, grit blasting, and bristle blasting. Bonded plate specimens, using end-notched flexure format, with a thin adhesive epoxy layer were manufactured and tested, under mode II loading condition, in both static and dynamic tests. The results confirm the importance of surface treatment of the substrate on the fatigue life, confirming that adhesively bonded joints have significant performance differences when subjected to static and dynamic loadings.

BONE ANISOTROPY - ANALYTICAL AND FINITE ELEMENT ANALYSIS

A human femur model, submitted to static loads, is analyzed through the utilization of three material constitutive relationships, namely: isotropic, transversally isotropic and orthotropic. The influence of bone anisotropy with respect to principal stress/strain distribution on human femur external surface was accessed through the use of analytical and finite element approaches. The models results show that the principal angles at a medial path bone surface have a good correlation with human femur bone lamellae angles.

Elastoplastic Analysis of the Residual Stress in Chain Links

Mooring lines of offshore oil exploitation platforms consist of long lengths of steel chain links, wire ropes and other accessories. Usually, these lines are designed for an operational life of about 20 years and periodic inspections are mandatory for monitoring the structural integrity of these components. The failure of a single element in a mooring line can cause incalculable environmental damage and severe economic losses. The ocean adverse environment loading produced by the combination of the wind, waves and currents leads to a complex alternate loading that can promote fatigue and crack propagation. Residual stress plays a preponderant part in the structural integrity of a mechanical component subjected to such loading. Offshore mooring line components as chain links enter in operation with a residual stress field created by the proof test dictated by offshore standards. However, the traditional design of such mechanical components does not consider the presence of residual stress. This study concerns about predict the residual stress field present in stud and studless chain links prior to operation to compare the fatigue life predicted by the traditional design methodology with the one predicted considering the residual stresses states present before operation. Numeric simulations with an elastoplastic finite element model are used to estimate the residual stress along the chain link that are present after the proof test and before operation. The results indicate that the presence of residual stresses modify significantly the fatigue life of the component.Copyright

Corrosion Fatigue Behavior of Flexible Pipe Tensile Armor Wires in a CO2 Environment

The new offshore areas being explored in Brazil presents higher concentration of CO2 compared with most existing offshore fields. The presence of these more aggressive environments has led to the development of new technologies. Due to the construction characteristics of flexible pipes, any increase in CO2 concentration in the conveyed fluid will, in turn, increase the CO2 concentration in the pipe annulus, subjecting the metallic armor layers to a more aggressive environment. Evaluation of the CO2 effects of corrosion fatigue behavior in tensile armor wires is therefore of vital importance. A comprehensive corrosion fatigue experiment for tensile armor wires in environments up to 10 bar of CO2, has been established and the experimental results have shown a fatigue life reduction in the tensile amour wires due to higher levels of CO2.

ASSESSING THE NOTCH SENSITIVITY OF HIGH STRENGTH WIRES

HIGH STRENGTH WIRES, WHICH HAVE A POOR NOTCH SENSITIVITY PERFOR-MANCE, ARE CURRENTLY BEEN USED ON MANY OFFSHORE APPLICATIONS WHERE HIGH STRESSES WITHOUT YIELDING ARE DEMANDED. TO ASSESS THESE WIRES NOTCH SENSITIVITY, AN INTEGRATED APPROACH WAS IMPLEMENTED. AN EXPERIMENTAL PROGRAM WAS CONDUCTED, THROUGH THE REALIZATION OF FATIGUE TESTS TO OBTAIN THE FATIGUE LIMIT FOR NOTCHED AND NOTCHED FREE SPECIMENS TO ASSESS THE FATIGUE STRESS CONCENTRATION FACTOR. A NUMERICAL APPROACH USING FINITE ELEMENT METHOD, AND AN ANALYTICAL MODEL, AVAILABLE IN TECHNICAL LITERATURE, WERE USED TO ASSESS THE STRESS CONCENTRATION FACTOR. WITH BOTH RESULTS, THE NOTCH SENSITIVITY COULD BE OBTAINED.

Experimental Comparison of Tensile Armor Wires Using Strain Gages and Fiber Bragg Grating Techniques

Flexible pipes are being installed and operated in more marginal and challenging offshore conditions related to deep-water environments. Especially important is the accurate assessment of the remaining life of a flexible riser so operators can avoid costly premature change outs. So, emerging inspection and monitoring technologies are being several developed to achieve a comprehensive flexible pipes integrity approach.For unbonded flexible pipes, the primary challenges include fatigue life, collapse, axial compression loading of the tensile armor wires and end fitting development.This paper is related to end fitting development area, due to necessary folding/unfolding process on the tensile armor wires during pipe assembling. This mechanical forming generates high levels of plastic strain on the wires, which may therefore reduce the fatigue life of the flexible pipe in the field.This paper presents an analysis of the high strain level involved in the folding and unfolding process along tensile armour wire, using the strain gages and fiber Bragg grating techniques.Besides that, this paper describes a comparison analysis, which correlates the performance of both methods to assess high strain levels.Copyright

Finite Element Residual Stress Analysis Applied to Offshore Studless Chain Links

The increasing expansion of deepwater petroleum activities has resulted in new challenges to the design of mooring systems. The complex mooring systems load history, which consists in a combination of wind, waves and currents, could induce nucleation and propagation of cracks in mooring line components. The failure of a single element in a mooring line of an offshore oil exploitation platform can produce incalculable environment damage as well as human and material losses. Offshore mooring line components like chain links must be submitted to a mandatory proof test, dictated by offshore standards, where loads higher than operational loads are applied to the mechanical component, resulting in high levels of residual stresses. Nevertheless, its presence is not considered in traditional design methodologies. Therefore, it is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. In this article, a comparative study is developed considering different approaches: two bidimensional finite element models, two tridimensional finite element models and an analytic model. These analyses establish the drawbacks and goals of using simpler models in the prediction of studless chain links stress distributions and in their fatigue lives. The four finite element models consider large displacements, plasticity and contact phenomena. Moreover, a simple fatigue life analysis is presented, based on SN curve, considering the effect of residual stresses in studless chain links before operation, that is, with loads caused by the proof test.Copyright

Analysis of the Influence of Mechanical Properties on the Residual Stress in Offshore Chain Links Using the Finite Element Method

Production offshore units have a relative long operational life (about 20 years), during which are submitted to the ocean adverse environment loading produced by the combination of wind, waves and currents. This complex loading history can promote the nucleation and propagation of cracks in mooring line components. The presence of defects establishes a critical situation that can lead to catastrophic failures. In spite of residual stress plays a preponderant part in the structural integrity of a mechanical component, the presence of residual stress is not considered in traditional design of these mechanical components. Therefore, is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. The present contribution regards on modeling and simulation of the residual stress distributions in studless chain links using a tri-dimensional elastoplastic finite element model with large displacements. In the analysis three material conditions, associated with different mechanical properties, were considered. The results indicate that the presence of residual stresses modify significantly the stress distribution in the component. Also, residual stress distribution depends on the mechanical properties of the chain link material. The structural integrity of the mechanical component was studied using the concept of critical volume associated to the material volume susceptible to a certain critical crack size. This methodology permits the evaluation of the critical crack length distribution related to brittle fracture of the component.© 2003 ASME

Analysis of the Transmissibility of the Rear Suspension of a Mini-Baja Vehicle

This work presents a dynamical analysis of the transmissibility of an off-road vehicle rear suspension, which was developed in CEFET-RJ for the Mini-Baja / SAE-Brazil competition. A finite element model was developed to identify the critical points of the structure. Afterwards, electric strain gages were bonded at the most critical points to measure the dynamic strains due to an impact load. Accelerometers were bonded before and after rear suspension system to measure the main transmissibility characteristics of the suspension. The data obtained through an A/D converter with instrumentation software was used to evaluate the transmissibility of the rear suspension and other important dynamic characteristics. Finally, a simple twodegree of freedom model was developed to study the behavior of the rear suspension and the influence of the main parameters in the transmissibility of accelerations and loads to the structure. An estimate for an optimal suspension adjustment was obtained with this simple model. The results obtained with this methodology indicates that it can be used as an effective tool for the design and improvement for Mini-Baja vehicle, as the designer can work with more realistic loads. INTRODUCTION The Mini-Baja vehicle is completely developed and built by undergraduate engineering students with the orientation of a professor board. During the development, the students are exposed to a real engineering problem involving several areas of knowledge. CEFET-RJ participates on the SAE competition since 1997. In the competition these vehicles are submit to several tests that exposed it to severe conditions, where should respect technical and safety SAE standards. These vehicles are highly competitive which demands an optimized project using advanced technologies. Figure 1 shows the CEFETRJ vehicle that participated on the 1998 SAE event. During the design process of the Mini-Baja structure it is necessary to quantify the maximum loads in the suspension and the accelerations and loads transmitted to the structure by the suspension. Usually, in the design of a vehicle, a static analysis is developed considering a static load that is equivalent to the maximum dynamic load. The equivalent static load is estimated using factors obtained in literature. These factors are generally quite conservative and they strongly depend on the suspension type. It is well know