Influence of shot peening and hard chromium electroplating on the fatigue strength of 7050-T7451 aluminum alloy

Chromium electrodeposition is a technique for the production of functional coatings on engineering components. These coatings are extensively micro-cracked and present high level of hardness, resistance to corrosion and wear and low coefficient of friction. In this paper the shot peening influence on the fatigue strength of aluminum 7050-T7451 alloy chromium electroplated, was investigated.The shot peening process was carried out to create residual stresses using ceramic and glass shots. A hard chromium electroplated coating of 100 mu m thickness was performed on the base material and the shot peened base material surfaces. S-N curves were obtained in axial and bending fatigue tests and compared with the 7050-T7451 aluminum alloy. In order to study the influence of residual stresses on fatigue life, the behavior of compressive residual stress field was measured by an X-ray tensometry.An increase in the axial fatigue strength of 25% and 50% of ceramic and glass shots, respectively, was observed. The lower performance in fatigue life for ceramic-shot peening may be attributed to higher surface damage, as a consequence of the overpeening intensity performed. However, in bending fatigue the behavior was practically equivalent for both processes. Fracture surface analysis by scanning electron microscopy was used to observe crack origin sites from shot peened and chromium electroplated samples. (C) 2006 Elsevier Ltd. All rights reserved.

Hygrothermal effects on damping behavior of metal/glass fiber/epoxy hybrid composites

Continuous fiber/metal laminates (FML) offer significant improvements over current available materials for aircraft structures due to their excellent fatigue endurance and low density. Glass fibers/epoxy laminae and aluminum foil (Glare) are commonly used to obtain these hybrid composites. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. Usually, epoxy resins absorb moisture when exposed to humid environments and metals are prone to surface corrosion. Therefore, the combination of the two materials in Glare (polymeric composite and metal). can lead to differences that often turn out to be beneficial in terms of mechanical properties and resistance to environmental influences. In this work. The viscoelastic properties. such as storage modulus (E') and loss modulus (E'), were obtained for glass fiber/epoxy composite, aluminum 2024-T3 alloy and for a glass fiber/epoxy/aluminum laminate (Glare). It was found that the glass fiber/epoxy (G/E) composites decrease the E' modulus during hygrothermal conditioning up to saturation point (6 weeks). However, for Glare laminates the E' modulus remains unchanged (49GPa) during the cycle of hygrothermal conditioning. The outer aluminum sheets in the Glare laminate shield the G/E composite laminae from moisture absorption. which in turn prevent, in a certain extent, the material from hygrothermal degradation effects. (c) 2005 Elsevier B.V. All rights reserved.

Evaluation of WC-17Co and WC-10Co-4Cr thermal spray coatings by HVOF on the fatigue and corrosion strength of AISI 4340 steel

It is known that chromium electroplating is related to the reduction in the fatigue strength of base metal. However, chromium results in protection against wear and corrosion combined with chemical resistance and good lubricity. Environmental requirements are an important point to be considered in the search for possible alternatives to hard chrome plating. Aircraft landing gear manufactures are considering WC thermal spray coating applied by the high-velocity oxygen-fuel (HVOF) process an alternative candidate, which shows performance at least comparable to results, obtained for hard chrome plating. The aim of this study is to compare the influence of WC-17Co and WC-10Co-4Cr coatings applied by HVOF process and hard chromium electroplating on the fatigue strength of AISI 4340 steel, with and without shot peening. S-N curves were obtained in axial fatigue test for base material, chromium plated and tungsten carbide coated specimens. Tungsten carbide thermal spray coating results in higher fatigue strength when compared to hard chromium electroplated. Shot peening prior to thermal spraying showed to be an excellent alternative to increase fatigue strength of AISI 4340 steel. Experimental data showed higher axial fatigue and corrosion resistance in salt fog exposure for samples WC-10Co-4Cr HVOF coated when compared with WC-17Co. Fracture surface analysis by scanning electron microscopy (SEM) indicated the existence of a uniform coverage of nearly all substrates. (C) 2004 Elsevier B.V. All rights reserved.

Correlation of microcrack fracture size with fatigue cycling on non-crimp fabric/RTM6 composite in the uniaxial fatigue test

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fatigue strength of HVOF sprayed Cr(3)C(2)-25NiCr and WC-10Ni on AISI 4340 steel

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fractography analysis and fatigue strength of carbon fiber/RTM6 laminates

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evaluation of WC-10Ni thermal spray coating with shot peening on the fatigue strength of AISI 4340 steel

Fatigue failure is a result of a crack initiation and propagation, in consequence of a cyclical load. In aeronautical components as landing gear the fatigue strength is an important parameter to be considered in project, as well as the corrosion and wear resistance.The thermal sprayed HVOF technology it's normally used to protect components against wear and corrosion, and are being considerate an alternative to replace chromium by the aeronautical industry. With respect to fatigue life, the HVOF technique induces residual stress on the interface. In the case of tensile residual stresses, the initiation and propagation phases of fatigue process are accelerated; on the other hand, compressive residual stresses close to the surface may increase fatigue life. The technique to improve the coated materials fatigue strength is the shot peening process, which induces residual stress in the surface in order to delay the nucleation and propagation process.The aim of present study is to compare the influence of WC-10 Ni coating applied by HVOF on the fatigue strength of AISI 4340 steel, with and without shot peening. S-N curves were obtained in axial fatigue tests for material base, and tungsten carbide coated specimens. (C) 2010 Published by Elsevier Ltd.

Describing fatigue crack growth and load ratio effects in Al 2524 T3 alloy with an enhanced exponential model

The fatigue crack behavior in metals and alloys under constant amplitude test conditions is usually described by relationships between the crack growth rate da/dN and the stress intensity factor range Delta K. In the present work, an enhanced two-parameter exponential equation of fatigue crack growth was introduced in order to describe sub-critical crack propagation behavior of Al 2524-T3 alloy, commonly used in aircraft engineering applications. It was demonstrated that besides adequately correlating the load ratio effects, the exponential model also accounts for the slight deviations from linearity shown by the experimental curves. A comparison with Elber, Kujawski and "Unified Approach" models allowed for verifying the better performance, when confronted to the other tested models, presented by the exponential model. (C) 2012 Elsevier Ltd. All rights reserved.

Power flow for primary distribution networks considering uncertainty in demand and user connection

This paper presents a method for calculating the power flow in distribution networks considering uncertainties in the distribution system. Active and reactive power are used as uncertain variables and probabilistically modeled through probability distribution functions. Uncertainty about the connection of the users with the different feeders is also considered. A Monte Carlo simulation is used to generate the possible load scenarios of the users. The results of the power flow considering uncertainty are the mean values and standard deviations of the variables of interest (voltages in all nodes, active and reactive power flows, etc.), giving the user valuable information about how the network will behave under uncertainty rather than the traditional fixed values at one point in time. The method is tested using real data from a primary feeder system, and results are presented considering uncertainty in demand and also in the connection. To demonstrate the usefulness of the approach, the results are then used in a probabilistic risk analysis to identify potential problems of undervoltage in distribution systems. (C) 2012 Elsevier Ltd. All rights reserved.

Prediction and probability of neonatal outcome in isolated congenital diaphragmatic hernia using multiple ultrasound parameters

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Analysis of a hyper-diverse seed dispersal network: modularity and underlying mechanisms

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of shot peening on the fatigue strength of anodized Ti-6Al-4V alloy

The increasingly design requirements for modern engineering applications resulted in the development of new materials with improved mechanical properties. Low density, combined with excellent weight/strength ratio as well as corrosion resistance, make the titanium attractive for application in landing gears. Fatigue control is a fundamental parameter to be considered in the development of mechanical components. The aim of this research is to analyze the fatigue behavior of anodized Ti-6Al-4V alloy and the influence of shot peening pre treatment on the experimental data. Axial fatigue tests (R = 0.1) were performed, and a significant reduction in the fatigue strength of anodized Ti-6Al-4V was observed. The shot peening superficial treatment, which objective is to create a compressive residual stress field in the surface layers, showed efficiency to increase the fatigue life of anodized material. Experimental data were represented by S-N curves. Scanning electron microscopy technique (SEM) was used to observe crack origin sites.

Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy

The tendency of the aircraft industry is to enhance customer value by improving performance and reducing environmental impact. In view of availability, aluminum alloys have a historically tendency to faster insertion due to their lower manufacturing and operated production infrastructure. In landing gear components, wear and corrosion control of many components is accomplished by surface treatments of chrome electroplating on steel or anodizing of aluminum. One of the most interesting environmentally safer and cleaner alternatives for the replacement of hard chrome plating or anodizing is tungsten carbide thermal spray coating, applied by the high velocity oxy fuel (HVOF) process. However, it was observed that residual stresses originating from these coatings reduce the fatigue strength of a component.An effective process as shot peening treatment, considered to improve the fatigue strength, pushes the crack sources beneath the surface in most of medium and high cycle cases, due to the compressive residual stress field induced. The objective of this research is to evaluate a tungsten carbide cobalt (WC-Co) coating applied by the high velocity oxy fuel (HVOF) process, used to replace anodizing. Anodic films were grown on 7050-T7451 aluminum alloy by sulfuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on axial fatigue strength of anodic films grown on the aluminum alloy surface is to degrade the stress-life performance of the base material. Three groups of specimens were prepared and tested in axial fatigue to obtain S-N curves: base material, base material coated by HVOF and base material shot peened and coated.Experimental results revealed increase in the fatigue strength of Al 7050-T7451 alloy associated with the WC 17% Co coating. on the other hand, a reduction in fatigue life occurred in the shot peened and coated condition. Scanning electron microscopy technique and optical microscopy were used to observe crack origin sites, thickness and coating/substrate adhesion. (c) 2007 Elsevier B.V. All rights reserved.

Fabrication of novel light-emitting devices based on green-phosphor/conductive-polymer composites

We report on light-emitting devices based on a green-phosphor compound (Mn-doped zinc silicate, Zn2SiO4: Mn) dispersed in a conductive polymeric blend (poly-o-methoxyaniline/polyvinylene fluoride, POMA/PVDF-TrFE). The devices exhibited high luminance in the green, good stability and homogeneous brilliance over effective areas up to 5 cm(2). The electroluminescence (EL) spectrum presented essentially the same characteristics as the photoluminescence (PL) and cathodoluminescence spectra, indicating that the light emission originates from decay of the same excited species, regardless of the excitation source. Operating characteristics were analyzed with current density - voltage (J - V) and luminance voltage ( L - V) curves to investigate the nature of the electroluminescence of the active material, which is still not completely understood.

Smart structures health monitoring using artificial neural network

This paper presents a non-model based technique to detect and locate structural damage with the use of artificial neural networks. This method utilizes high frequency structural excitation (typically greater than 30 kHz) through a surface-bonded piezoelectric sensor/actuator to detect changes in structural point impedance due to the presence of damage. Two sets of artificial neural networks were developed in order to detect, locate and characterize structural damage by examining changes in the measured impedance curves. A simulation beam model was developed to verify the proposed method. An experiment was successfully performed in detecting damage on a 4-bay structure with bolted-joints, where the bolts were progressively released.