The internal stress states of Optimized ZIRLO (OPZ) samples are evaluated post-quenching from increasing temperatures to determine the role of chromium coatings, oxidation, and microstructural ...reorienting on internal stress state. Before substantial oxide development (under 700 °C), uncoated tubular samples freely expand and do not accumulate significant global internal stress. As a stable, passivizing oxide develops (700–900 °C), a complex stress state develops with both the interior and exterior oxides in hoop compression. The internal tensile stress increases until the sample fully oxides, and biaxial stress is released through tortoiseshell-like cracking mechanisms. When a chromium coating is introduced, the initial stress states at low temperatures are higher than the uncoated samples due to Cr-coating application techniques and material differences between Cr and OPZ. At higher temperatures (700–1100 °C), the Cr-coated samples undergo a much simpler stress state than the uncoated samples due to the tensile hoop stress state of the Cr-coating caused by differing thermal expansion and the compressive state of the internal oxide caused by a Pilling-Bedworth ratio > 1. The subsequent film cracking mechanisms also differ from the uncoated samples. The smoother stress state experienced by the Cr-coated vs uncoated OPZ samples allows the Cr-coated samples to maintain the circular geometry that is vital to their protective application in nuclear reactors.
Display omitted
•The mechanism of residual stress relaxation in carburized steel was elucidated.•The compressive residual stress relaxation was attributed to compressive yielding.•The fatigue limit ...was estimated considering residual stress relaxation.•The compressive residual stress contributing to increased fatigue limit was revealed.
The mechanism of residual stress relaxation for carburized steels was elucidated and their fatigue limit was estimated. The compressive residual stress in the carburized steel after rotating bending fatigue tests is mainly influenced by the relaxation during the compressive loading phase, although it increases at the early stage. The fatigue limit of carburized steels can be estimated according to the modified Goodman diagram considering the residual stress relaxation. The proposed equation shows the maximum value of the fatigue limit (1013 MPa) of carburized steel and the maximum value of the compressive residual stress contributing to the increased fatigue limit.
Display omitted
This work aims at quantitative analysing the effect of different microstructures on the velocity at stress-free and stress coefficient (K) of longitudinal critical refraction (LCR) ...wave in measuring welding residual stress process, ameliorating the traditional LCR wave method for improving its’ effectiveness and accuracy. The longitudinal critically refracted wave attenuation velocity (LCR-AV) method was proposed in the evaluation of residual stresses in A7N01 welded joints. The same initial status base materials samples are used to produce different levels of grain size and precipitation by heat treatment technology, obtained the velocity at stress-free and attenuation of LCR wave. As expected, the voltage amplitude changes linearly with velocity and stress coefficient, and the precipitation effect can be ignored. The LCR-AV method based on the liner relationship between velocity, attenuation and grain size are efficient to decrease the errors resulting from the different microstructure (base metals, heat-affected zones, and welded zones). Differ with the traditional LCR waves method, the LCR-AV method also measures the voltage amplitude, and the measured results of LCR-AV method compared with those obtained by the hole-drilling reference method shows more sufficient measurement reliability and precision. It shows that LCR-AV method is a valuable quantitative technology to estimate the residual stress of welded joints.
In most literature, the residual stress distribution is assumed to be a symmetrically 2nd order polynomial with compressive stresses near the surface, balanced by tensile stresses in the centre. This ...assumption leads directly to the assertion that the thickness of the compressive layer is 21.1% of the total thickness. The present paper experimentally investigates the accuracy of this well-established rule for thermally tempered glass and develops a simple equation for asymmetric stress distributions.
The experimental investigation is based on more than 6000 measurements of commercially tempered (and heat-strengthened) soda lime silica glass and provides statistics for the compressive zone depth. The dependency of the thickness, residual stress state, and the effect of asymmetric stress distributions is investigated.
Due to the scattering in the experimental results, an FE-model has been applied to clarify the effect from the different parameters.
•A large experimental campaign is investigating the compressive zone depth in tempered glass.•Commonly used assumptions are investigated and deviations are reported.•FE models are used for investigating the theoretical influence of different parameters on the compressive zone depth.
The deposition of ternary nitrides with the incorporation of carbon atoms into its structure has demonstrated to be a promising approach in the pursuit of wear-resistant and self-lubricating ...coatings. Firstly, both TiAlN and TiAlCN monolayers were deposited using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) onto quenched and tempered AISI H11 tool steel to be used as references. Acetylene was used as a carbon precursor, producing DCMS and HiPIMS TiAlCN coatings with 9.0 and 21.7 at.% C, respectively.
Subsequently, TiAlN/TiAlCN multilayers of various designs were also developed as follows: 5×10/500, 5×50/500 and 5×100/500 nm. Residual stresses of the coating systems were determined by X-ray radiation utilising an ETA-diffractometer with a Cu-Kα radiation source applying the sin2ψ method. Additionally, residual stresses depth gradients of the substrate before and after the deposition of the coatings were determined in a LEDDI 8-circle diffractometer equipped with a W-X-ray tube and operated in the energy-dispersive mode of diffraction. Great reduction of the compressive residual stresses in the coatings was observed after the introduction of carbon into the TiAlN coating structure, shifting from −1047 ± 149 to −307 ± 211 MPa for the DCMS and from −7035 ± 1361 to +989 ± 187 MPa for the HiPIMS coatings. In the multilayer coatings, compressive residual stresses increase along with the increment of the TiAlN interlayer. Additionally, residual stresses of the substrate in the near-surface are dragged from low compressive stresses (−218 ± 61) to tensile stresses in the range of 1000 to 2000 MPa for all the DCMS/substrate systems, a behaviour only presented in HiPIMS by the TiAlN monolayer. Wear coefficients of all the evaluated HiPIMS systems are notoriously lower than their DCMS counterparts. Compared to TiAlN, TiAlCN HiPIMS presented a lower coefficient of friction but a higher wear coefficient, which in turn was not reduced by the introduction of the multilayer systems. Finally, Scratch test and Rockwell C adhesion tests have shown higher adhesion of DCMS coatings than HiPIMS coatings, and a detriment of the monolayers adhesion by the implementation of TiAlN/TiAlCN multilayer systems. The understanding of the residual stresses, both in the coating and in the substrate, and the way they affect the tribomechanical performance of the system coating/substrate continues to be of great importance, especially for coatings deposited by new technologies such as HiPIMS and self-lubricating coatings.
•Great reduction of compressive residual stresses with the carbon inclusion in TiAlN.•High superficial residual stresses on the substrate after DCMS deposition.•Adhesion of DCMS coatings systems to AISI H11 is always higher than HiPIMS.•Ceramic/ceramic multilayer designs did not improved adhesion or wear.
Metal additive manufacturing (MAM) technology has great application potential in the aerospace, medical and energy fields with its high material utilization efficiency to achieve the manufacturing of ...metal parts of any shape. However, the extreme thermal, mechanical, and metallurgical coupling in MAM process leads to large residual stresses in the manufactured samples. Residual stress has a significant effect on the dimensional stability, corrosion resistance, crack growth resistance and mechanical properties of MAM samples. As a result, residual stress can be regarded as a key factor in controlling costs, enhancing product efficiency and quality. To help researchers and engineers attain up-to-date information and knowledge about residual stress in MAM, the current paper provides a comprehensive review in this field, especially the formation mechanisms, the influence of process parameters, prediction and control methods.
In this study a model by novel analytical approach is developed and experimentally verified for shot peening residual stress distribution. The residual stress field induced by single shot impact is ...calculated by using Glinka–Molski energy-based method and kinematic hardening model. The formulation of the compressive residual stress (CRS) distribution is often based on plane strain or plane stress. It can be determined from the derived relation presented in this paper, the final residual stress in the full coverage conditions is the average of the two strain and stress plane expressions proposed by previous researchers. The distribution of residual stress is one of the key differences between the profiles produced by the results of the current model. There is a significant distinction between surface residual stress and maximum CRS, because the CRS profile near the surface is more curved compared to profiles obtained in earlier analytical models. The experimental data obtained by XRD analysis indicate the correctness and precision of the current model. Another goal of this study is to increase the fatigue life of GTD-450 stainless steel by shot peening at two different peening intensities. The fatigue life of samples were obtained by rotary bending test. Analytical results that confirmed by experimental findings shown bigger maximum compressive residual stresses occurred in higher shot peening intensities. This incident can improved fatigue life by deeper plastically deformed layer.
•A random multi-shots peening model considering the initial hardness gradient and residual stress conditions of a carburized rollers is developed.•The influence of shot peening coverage on detail ...evolution of surface morphology and residual stress is investigated.•The ratio between the layer thickness of compressive residual stress and the critical depth of maximum compressive stress generally lies in the regime of 3.6–4.3 after shot peening.
Shot peening is becoming a widely used surface strengthening technique for various key mechanical components for its enhanced influence on the fatigue performance. This technique allows to strengthen the mechanical properties of material via introduce a certain depth of compressive stress layer and change the surface topography. The relation of the shot peening processing parameters, the surface integrity including residual stress and the surface roughness remains a large unmet practical need. In this paper, the residual stress and surface topography obtained by various shot peening treatments were experimentally and theoretically examined. A random multi-shots peening model of a carburized roller, accounting for the initial hardness gradient and residual stress was developed. The measured residual stress and surface roughness present good agreements with the predicted results. Both the experimental and simulated results reveal that the axial and tangential residual stress components tend to be consistent after shot peening. In addition, the influence of peening coverage on detailed evolution of surface topography and residual stress is investigated. It is found that the ratio between the layer thickness of compressive stress and the critical depth of maximum stress generally lies in the regime of 3.6–4.3 after shot peening. As the coverage increases from 100% to 400%, surface roughness parameters Sa, Sq, S5z, Sku decrease, while the maximum magnitude of compressive stress fluctuates in the range of 1105∼1230 MPa. This work could act as an advisory reference for shot peening engineering practices.
Display omitted
•Residual stress mapping provides an efficient alternative to welding process simulations.•Upper bound distributions of experimental data secure conservatism in integrity assessments.•Internal ...equilibrium in the FE model play important role in residual stress mapping.
Residual stress is a factor which potentially affects the integrity of welded components. We have developed a methodology of assessment to establish the state of residual stress in a butt-welded plate by using a limited set of experimental measurements obtained using neutron diffraction. The unique longitudinal and transverse residual stress components, as a result of the welding process, are measured across the weld in three depths through the thickness. The measured residual stresses are then used to estimate a stress distribution for each stress component. The estimated stress distribution is then mapped to a finite element model of the weld plate, before adopting an iterative solution to reconstruct the residual stress fields. In addition, a traditional welding simulation is performed using the same weld plate details to predict and compare the residual stress distributions. It is shown that accurate residual stress field reconstruction is possible in and around the area of measurement using the limited measurement data from the neutron diffraction technique. In the estimated stress profiles, an upper-bound distribution is implemented in the weld and Heat Affected Zone (HAZ). This increases the efficiency and reduces the complexity of modelling. In the meantime, conservatism in the estimated stress is secured.
PDF
