Showing papers on "Peening published in 2009"

Fatigue Behaviour of Welded High-Strength Steels after High Frequency Mechanical Post-Weld Treatments

Abstract: Investigations have been carried out regarding the fatigue strength of welded details improved by high frequency treatment methods. These methods increase the fatigue strength by cold forming of the surface, so that the weld toe is smoothened, the surface hardness is increased and compressive residual stresses are present up to a depth of 1 to 1.5 mm. In this paper, the surface residual stresses at the weld toe are investigated before and after different loading conditions and for different steel grades. It is shown that only high tensile fatigue loading can lead to a slight residual stress relaxation for low-strength steels. The fatigue crack behaviour is analysed in more detail. The crack propagation rates with and without surface treatment are investigated, using defined lines of rest. The study shows that crack propagation in the edge layers is reduced. Several cracks may start in the UIT-treated zone but will not propagate further, until one final crack, often close to the edge of the specimens, will lead to failure. The results of fatigue tests for butt welds and longitudinal stiffeners improved by high frequency hammer peening are presented. The fatigue strength is seen to be doubled. For high-strength steels, the improvement at different load levels is identical, but for lower-strength steels, high stress ranges lead to reduced improvement. This fact results in flatter SN-curves and can be explained by the lower maximum of residual stresses and residual stress relaxation.

Material model validation for laser shock peening process simulation

Abstract: Advanced mechanical surface enhancement techniques have been used successfully to increase the fatigue life of metallic components. These techniques impart deep compressive residual stresses into the component to counter potentially damage-inducing tensile stresses generated under service loading. Laser shock peening (LSP) is an advanced mechanical surface enhancement technique used predominantly in the aircraft industry. To reduce costs and make the technique available on a large-scale basis for industrial applications, simulation of the LSP process is required. Accurate simulation of the LSP process is a challenging task, because the process has many parameters such as laser spot size, pressure profile and material model that must be precisely determined. This work focuses on investigating the appropriate material model that could be used in simulation and design. In the LSP process material is subjected to strain rates of 106 s−1, which is very high compared with conventional strain rates. The importance of an accurate material model increases because the material behaves significantly different at such high strain rates. This work investigates the effect of multiple nonlinear material models for representing the elastic–plastic behavior of materials. Elastic perfectly plastic, Johnson–Cook and Zerilli–Armstrong models are used, and the performance of each model is compared with available experimental results.

Investigation on the non-homogeneity of residual stress field induced by laser shock peening

Abstract: Laser shock peening can impart compressive residual stresses in the target material, which is an innovative surface treatment technique similar to shot peening. But when laser intensity exceeds a threshold, the lower residual stress at the center of the laser shocked zone compared to those away from the center will be induced. This phenomenon is closely related to the rapid and complex response of target material during the treatment. A complete numerical model, as an effective way to investigate the shock–solid interaction, is conducted to simulate the process and is experimentally validated by the surface deformation of target material subjected to multiple impacts. Dynamic responses of target material including surface displacements, stresses and strains, are analyzed in detail based on the model. The residual stress drop at the center is found to be induced by the reverse plastic loading due to the boundary effect of laser shock. And adopting square laser spots should attenuate the simultaneous focalization of release waves and decrease the residual stress drop.

Residual stress field and thermal relaxation behavior of shot-peened TC4-DT titanium alloy

Abstract: Shot peening is an effective surface treatment method, which can improve the fatigue properties of metallic materials. In the present paper, the residual compressive stress field induced in TC4-DT titanium alloy under different shot peening conditions and the thermal relaxation behaviors of shot-peened TC4-DT were discussed. The shot peening can cause residual compressive stress on the material surface compared to un-peened materials. The subsurface residual stress distributions of original and shot-peened specimens were measured by an X-ray diffraction method. The residual compressive stress profiles accord with the characteristic curve of residual stress field. The maximum residual compressive stress is located at subsurface layer. Surface roughness also increases with increasing shot peening intensity. There is relaxation of residual compressive stress during temperature. Thermal relaxation behavior of residual stress was studied at 150 and 300 °C with different ageing time. The residual stress relaxation is influenced by temperature and time during ageing. Thermal relaxation of residual stress is a thermal recovery process. The relaxation process of thermal residual stress is analyzed by applying the Zener–Wert–Avrami function.

Modelling of residual stresses in the shot peened material C-1020 by artificial neural network

Abstract: This study consists of two cases: (i) The experimental analysis: Shot peening is a method to improve the resistance of metal pieces to fatigue by creating regions of residual stress. In this study, the residual stresses induced in steel specimen type C-1020 by applying various strengths of shot peening, are investigated using the electrochemical layer removal method. The best result is obtained using 0.26mmA peening strength and the stress encountered in the shot peened material is -276MPa, while the maximum residual stress obtained is -363MPa at a peening strength of 0.43mmA. (ii) The mathematical modelling analysis: The use of ANN has been proposed to determine the residual stresses based on various strengths of shot peening using results of experimental analysis. The back-propagation learning algorithm with two different variants and logistic sigmoid transfer function were used in the network. In order to train the neural network, limited experimental measurements were used as training and test data. The best fitting training data set was obtained with four neurons in the hidden layer, which made it possible to predict residual stress with accuracy at least as good as that of the experimental error, over the whole experimental range. After training, it was found the R^2 values are 0.996112 and 0.99896 for annealed before peening and shot peened only, respectively. Similarly, these values for testing data are 0.995858 and 0.999143, respectively. As seen from the results of mathematical modelling, the calculated residual stresses are obviously within acceptable uncertainties.

Magneto-Acoustic Emission and Magnetic Barkhausen Emission for Case Depth Measurement in En36 Gear Steel

Abstract: There is a need in industry to supply safe, economical, and reliable techniques to characterize surface treatments such as case hardening and peening of steel components and structures, both at the manufacturing stage and in service. Magnetic Barkhausen emission (MBE) has proved successful for these tasks, but has severe limitations in terms of measurement depth of the technique and deeper treatments such as laser peening and case hardening often fall outside the scope of MBE inspection. The domain wall motion that generates MBE also causes a release of elastic energy known as magneto-acoustic emission (MAE), which has a much greater measurement depth, and so offers a complementary technique to extend the measurement depth for the characterization of surface treatments in steel. In this paper, comparative MBE and MAE results from case hardened En36 gear steels are presented in the form of signal profiles and correlations are drawn between MBE and MAE profile features and domain activity within the soft core and the case hardened layer. The results show that the overall amplitudes for both MBE and MAE exhibit a good correlation with case depth, but profile analysis for MAE is ambiguous, so possible interpretations of the MAE profile are discussed.

Effects of surfaces nanocrystallization induced by shot peening on material properties : a Review

Abstract: A brief description of surface nanosrystallization process via severe plastic deformation is presented. To come to the point different shot peening methods which have proved to be able to create nanocrystalline layers are demonstrated clarifying the actual state of the art. Then the influence of the process is reviewed on material behavior and a wide range of affected properties are investigated. On this basis some possible addresses for future research in this field are drawn and underlined.

Fatigue crack growth performance of peened friction stir welded 2195 aluminum alloy joints at elevated and cryogenic temperatures

Abstract: The effects of various surface treatments on fatigue crack growth and residual stress distributions in friction stir welded 2195 aluminum alloy joints were investigated. The objective was to understand the degree to which residual stress treatments can reduce fatigue crack growth rates, and enhance fatigue life of friction stir welded components. Specimens were fabricated from 12.5 mm thick 2195-T8 aluminum plate, with a central friction stir weld along their length. Residual stresses were measured for three specimen conditions: as-welded (AW), welded then shot peened (SP), and welded then laser peened (LP). Crack growth rate tests were performed in middle-cracked tension specimens under constant amplitude load for each of the three conditions (AW, SP, LP) and at three temperatures (room, elevated, and cryogenic). At room and elevated temperature, crack growth rates were similar in the AW and SP conditions and were significantly lower for the LP condition. At cryogenic temperature, it was difficult to discern a trend between residual stress treatment and crack growth rate data. Laser peening over the friction stir welded material resulted in the fatigue crack growth rates being comparable to those for base material.

Evaluation of Residual Stresses Induced by Robotized Hammer Peening by the Contour Method

Abstract: Welded components suffer from high tensile residual stresses close to the weld beads. These stresses seem to be the origin of premature cracking which could result in a catastrophic rupture during operation and a reduction of the lifespan of these components. In this context, the Hydro-Quebec’s Research Institute (IREQ) developed a technique of residual stresses relaxation by robotized hammer peening which makes it possible to release stresses close to surface and preserve the mechanical and dimensional properties of manufactured components. Robotized hammer peening was used to induce compressive residual stresses on initially stress free samples of austenitic stainless steel 304L. Hammer peening layers from one to nine were performed and the resulting residual stresses were evaluated thanks to the contour technique. Complete 2D residual stress fields on samples cross sections were obtained. The ability of hammer peening to relax residual stresses within welded plates was then quantified on austenitic stainless steel 304L plates welded with a 308 steel and hammer peened. These tests show the efficiency of hammer peening as a method to relax tensile residual stresses and induce compressive ones to a depth of a few millimetres. Process parameters were optimized such as the number of hammer peening layers to be applied to reduce processing time and maximization of the intensity and spatial distribution of the compressive residual stresses.

Shot, devices, and installations for ultrasonic peening, and parts treated thereby

Abstract: A system for ultrasonically peeing surfaces includes a sonotrode comprising a body material and a vibrating surface, the vibrating surface coated with a coating material having a hardness greater than the body material, a treatment chamber defined at least in part by the vibrating surface, and at least one piece of shot within the treatment chamber to be excited by the vibrating surface of the sonotrode, the at least one piece of shot having a hardness greater than or equal to 800 HV.

Effect of shot peening on the fatigue behaviour of cast magnesium A8

Abstract: Shot peening is known to improve the fatigue performance of structural metallic materials. The improvement in fatigue life is derived primarily from compressive residual stresses that are introduced into the near-surface of the components and which hinder crack initiation and growth. Magnesium alloys are finding increasing use in automotive applications, but their relatively low strength means that they are highly susceptible to fatigue failures. This is particularly the case for cast alloys which may contain high levels of porosity. Shot peening may be of use, but the beneficial effect of the compressive stress may be offset by the surface damage associated with peening of a soft material. In this study the fatigue life of sand-cast A8 magnesium alloy has been investigated before and after a shot peening treatment to investigate whether shot peening is beneficial for a component with this combination of relatively low strength and relatively poor initial surface finish. Previous studies into the effect of shot peening on magnesium alloys have been limited to wrought alloys and there has been little work on the influence of shot peening on cast magnesium alloys. The residual stress before and after peening was determined by incremental hole drilling which shows that the peening process generated a compressive residual stress in the cast specimens. The fatigue results show that the fatigue life is significantly improved by the shot peening process, and there is also an improvement in the endurance limit. An increase in the surface roughness of the samples was found after peening but this was not found to be detrimental to the fatigue performance.

Method and device for strengthening surface modification by combination of laser cladding and laser peening

Abstract: The invention provides a method for modifying a composite surface based on laser cladding and combining laser shock peening, and a device thereof. The method provided by the invention is characterized in that a coaxial and powder feeding type fast axial flow CO2 laser cladding unit clads a layer of coating on the surface of a substrate; then a neophane glass impulse laser shock peening unit is used for the shock peening on the surface of the cladded coating; a measurement feedback system is utilized to detect the surface roughness and the distribution state of residual stress of the cladded coating; the precise control over the surface roughness and the residual stress of the coating is realized by a central control and processing system so as to obtain a high quality surface-cladded coating with good performance. The device comprises the coaxial and powder feeding type laser cladding unit, the laser shock peening unit, a digital control working system, the measurement feedback system and the central control and processing system, and is under integrated control by a computer. The method and the device of the invention can reduce residual tensile stress and improve the quality of the cladded coating and prolong the service life thereof.

Abrasive waterjet peening with elastic prestress: A parametric evaluation

Abstract: Abrasive waterjet peening (AWJP) has emerged as a potentially viable method of surface treatment for metal orthopedic devices. In this study the influences of AWJP with elastic prestress on the surface and subsurface residual stress distributions and surface texture of spring steel (ASTM 228) as well as titanium (Ti6Al4V) and nickel (inconel 718) alloys were studied. A design of experiments (DOE) and an analysis of variance (ANOVA) were used to identify the parameters with primary contributions to the dependent variables. Surface residual stress resulting from AWJP ranged from 500 to 2500 MPa, and the depth of compressive residual stress ranged from nearly 80 to 600 μm. While the elastic prestress had no effect on the surface texture, it was a primary contributor to the magnitude of surface residual stress, which increased with an increase in the elastic prestress. According to the results of this study, AWJP with elastic prestress can serve as a viable method of surface treatment in situations that require an increase in surface roughness and a compressive residual stress.

Effect of Shot Peening on Surface Characteristics and Fatigue Properties of T5-Treated ZK60 Alloy

Abstract: The effects of shot peening on surface characteristics and high cycle fatigue (HCF) performance of T5-treated high-strength magnesium alloy ZK60 (named after ZK60-T5) were investigated. The glass bead with an average diameter of 0.35 mm was adopted for shot peening and the Almen intensity was arranged from 0.02 to 0.40 mmN. The surface microstructure and texture of ZK60-T5 are greatly changed by shot peening, and residual compressive stress is produced in the surface deformation layer. The magnesium alloy ZK60-T5 shows a pronounced overpeening effect. A marked improvement in fatigue life is obtained at low Almen intensities, namely the fatigue strength (at 10 7 cycles) increases from 150 to 195 MPa at the optimum Almen intensity of 0.05 mmN. The fatigue crack nucleation site of ZK60-T5 is also found from surface regions to the subsurface. [doi:10.2320/matertrans.MRA2008415]