Material Residual Stresses Research Articles

Experimental and numerical investigation on residual stress of 316L SS treated by different laser shock peening parameters

316 L stainless steel has excellent mechanical properties, but fracture occurs when working in some extreme environments for a long time. As one of the important surface treatment technologies, laser shock peening (LSP) can improve the mechanical properties by inducing compressive residual stress (CRS) within the material, and has been widely used in a variety of fields due to its outstanding capabilities. Since LSP produces significant CRS, the influence of different laser parameters on the residual stress distribution of 316 L stainless steel was studied by numerical simulation, and verified by experiments. The results reveals that with the increase of laser energy, the residual stress in the surface and depth direction of the material increases firstly and then decreases gradually; three LSP cycles were performed on the same material, and it was found that the surface CRS within material had only a slight increase with three LSP cycles compared to the one with two LSP cycles, indicating that the CRS had reached the saturation; the effect of LSP on the residual stress of materials under different spot shapes was also studied, which indicates that the square spot can achieve better strengthening effect for multi-point LSP. Furthermore, the reasons for the improvement of mechanical properties were analyzed through microstructure observation.

Machine learning in prediction of residual stress in laser shock peening for maximizing residual compressive stress formation

Laser Shock Peening (LSP) is an advanced technique for enhancing surface properties, drawing significant interest for its ability to induce beneficial residual stresses in materials. Traditional LSP design processes, reliant on manual parameter selection, often result in imprecise control over the stress distribution, necessitating multiple iterations and high costs. This study introduces a machine learning (ML)-based approach, utilizing the Random Forest (RF) algorithm, to automate and optimize the design of LSP parameters for nickel-aluminium bronze surfaces. Our findings demonstrate the RF model’s capability to accurately predict and optimize residual stress distributions, achieving compressive stresses up to 472 MPa with a notable reduction in design iterations. The model forecasts both uniform and non-uniform stress patterns, particularly identifying areas susceptible to Residual Stress Holes (RSH) with improved precision. With an Absolute Percentage Error (APE) of only 6.2 %, our approach significantly outperforms traditional ML algorithms, offering a novel method for efficiently designing complex residual stress fields in LSP applications.

Development of a dual-mode energy-resolved neutron imaging detector: High spatial resolution and large field of view

Energy-resolved neutron imaging is an effective way to investigate the internal structure and residual stress of materials. Different sample sizes have varying requirements for the detector's imaging field of view (FOV) and spatial resolution. Therefore, a dual-mode energy-resolved neutron imaging detector was developed, which mainly consisted of a neutron scintillator screen, a mirror, imaging lenses, and a time-stamping optical fast camera. This detector could operate in a large FOV mode or a high spatial resolution mode. To evaluate the performance of the detector, the neutron wavelength spectra and the multiple spatial resolution tests were conducted at CSNS. The results demonstrated that the detector accurately measured the neutron wavelength spectra selected by a bandwidth chopper. The best spatial resolution was about 20 μm in high spatial resolution mode after event reconstruction, and a FOV of 45.0 mm × 45.0 mm was obtained in large FOV mode. The feasibility was validated to change the spatial resolution and FOV by replacing the scintillator screen and adjusting the lens magnification.

Investigation of the influence of fatigue alternating loading on residual stress in materials

This study investigates the effect of pulsating cyclic fatigue loading on the internal stress of silicon steel material. A comparative analysis is conducted between the loaded material and the original material before treatment. The findings indicate that pulsating cyclic fatigue loading leads to a decrease in the residual stress of the material and an increase in its elongation, albeit with a reduction in its strength. Additionally, fatigue alternating loading reduces the roughness of the material and enhances its grain size, resulting in narrower grain boundaries. Transmission electron microscope (TEM) analysis indicates that finite fatigue loading causes an increase in the number of dislocations in the material, leading to local plastic deformation and contributing to the reduction of residual stress in the material. Notably, the mechanism underlying the reduction of residual stress resulting from pulsating cyclic fatigue loading is akin to that of non-temperature-affected residual stress reduction treatment, suggesting a possible similarity in their fundamental nature.

Determination of residual stresses in metallic materials based on spherical indentation strain

Abstract A spherical indentation strain method was proposed to determine surface residual stress in this study. Through numerical simulation, the effect of the material properties and residual stress on the plastic zone around the indentation was investigated, and the ideal strain measurement region appropriate for diverse materials was identified. Meanwhile, the presence of residual stress in material will cause the strain increment in the strain measurement area near the indentation to change. Based on the relationship among strain increment, residual stress and material mechanical properties, the calibration equation of residual stress for different materials were established. A portable residual stress loading device was developed and combined with the indentation test to calibrate the 316 L and 304 stainless steel of nuclear welding joint material. The reliability of this method was verified, and it provides convenience for the calibration of the residual stress of stainless steel materials.

Effect of grinding conditions of gears made of 20MnCr5 steel after single-piece flow heat treatment on the condition of the surface layer of the tooth working surface

The paper investigated the effect of selected processing conditions during gear grinding on the value and distribution of microhardness and residual stress formed in the technological surface layer of gears after thermochemical treatment (TCT) conducted by a continuous single-piece flow method.The gears were carburised with LPC at 920C, then quenched in a 4D Quenching chamber at 7 bar and tempered at 190C for 3 hours. In the next step, the working surfaces of the gear teeth were ground by supplying grinding fluid (GF) to the grinding zone using the WET method and the MQL method with a minimum amount. Measurements were made on the distribution of microhardness and residual stress formed in the technological surface layer of gears after thermochemical treatment and after the grinding process.The results of the study showed the influence of workpiece speed vw and the method of delivery to the grinding zone GF on selected parameters describing the condition of the technological surface layer of the teeth of gears made of 20MnCr5 steel. The grinding process with a white aluminium oxide grinding wheel causes deterioration in the material's residual stress state. For each of the three analysed workpiece speeds vw, smaller changes in microhardness with respect to the microhardness of the material before grinding occur in the surface layer of samples ground with GF fed with the MQL method. Similarly, residual stress values are in the area of favourable compressive stresses.Environmental considerations and the need to comply with increasingly stringent environmental protection and worker safety regulations are pushing researchers and entrepreneurs to completely eliminate or reduce the consumption of grinding fluids in the grinding process. Based on the research and analysis carried out in this study, it was concluded that applying minimum GF by the MQL method could be an alternative to the conventional WET method.In sustainable manufacturing, it is extremely important to produce high-quality items while reducing the cost of manufacturing and taking care of the environment and workers' health. This includes the manufacture of gears, a basic component used in gear transmissions in the automotive industry, for example. The research has established that it is possible to use the MQL method, which reduces the amount of GF used when grinding the working surfaces of gear teeth, as an alternative to the conventional WET method.The conducted research was the first to determine the most favourable conditions, in terms of the obtained residual stresses and microhardness, for grinding the working surface of gear teeth using the MQL method.

A Simulation Study on the Effect of Residual Stress on the Multi-Layer Selective Laser Melting Processes Considering Solid-State Phase Transformation.

The selective laser melting (SLM) manufacturing process is a complex process involving moving a molten pool, rapid non-equilibrium solidification and solid phase transformation. If the thermal residual stress is too large, it may lead to warping, cracking and failure of the structures. The present work aims to establish a thermo-mechanical framework to predict temperature evolutions, molten pool configurations and residual stresses of materials in the SLM process, based on the toolpath-mesh intersection method. Moreover, the influences of the laser power, process parameters and mesh size have been discussed. The stress concentration occurred at the interface between the melt layer and substrate results in warping deformation of the materials. This work provides a novel method to reveal the resulting physical mechanism inside the molten pool in terms of residual stresses and distortions.

Non-contact stress-strain characterization of aluminum alloy by laser-induced thermal-wave radar (LTR) imaging

Evaluation of the stress/strain state in alloys is usually performed by direct mechanical measurements, contact ultrasound or ionizing-radiation nondestructive testing (NDT). Safe and totally non-contact methods have considerable advantages and are worthy of further development. In this work, a novel active infrared NDT framework with a linear-frequency-modulated laser-induced thermal-wave radar (LFM-LTR) imaging modality was proposed to quantitatively analyze thermo-mechanical properties as a function of the changing external loading. Chirp-modulated laser emission generates a depth-resolved diffusion-wave field which is analyzed with a modified anisotropic LTR theory. Features of stress-induced thermal anisotropy within uniaxial loaded materials were parametrized and extracted from simulated LTR signals which form the basis for solving the inverse problem of determining tensorized thermo-mechanical properties. An LTR experimental setup was built and used to validate the foregoing theoretical model and numerical analysis. Experimental thermo-mechanical property variation throughout the tensile test was eventually determined in terms of the nominal conductivity tensor without using any contacting sensors. The proposed active infrared testing scheme is promising to facilitate remote and indirect sensing of residual stresses in materials.

Exploration of irreversible residual stresses in a carbon/epoxy composite

Residual stresses in composite material may rise from several sources; difference in thermal straining between fibre and matrix, chemical shrinkage of the matrix material. The presented paper explores an irreversible Eigen-strain in the material which is shown to change and be removed by a thermal treatment above the Tg of the matrix material. This has been observed though TMA measurements of a carbon/epoxy unidirectional sample. The local Eigen-strain is translated into stresses using a visco-elastic constitutive relation. Further exploration indicates that cooling rate influence the generation of residual stresses in the material.

Peculiarities of Formation of Residual Stresses in Welded Joints and Stellite Weld Cladding on Rail Steel

Using X-ray diffraction methods, the distributions of residual stresses over the cross section of a welded joint of the rail and in cladding of wear-resistant stellite have been analyzed. The stresses in the welded joint have been determined by the sin2ψ method, and the stresses in stellite cladding have been determined by an original method based on the analysis of the anisotropy of elastic characteristics of the material, which allows one to more accurately estimate the residual stresses in materials with a heterogeneous structure. It is established that the phase composition of rail steel (α-Fe and traces of cementite) in a welded joint remains unchanged over the cross section, while the original textureless state is preserved in all investigated regions of the welded joint. In a welded joint, compressive residual stresses ranging from –412 to –517 MPa in the direction normal to the weld and compressive residual stresses of above 300 MPa in the direction of rail width are formed. This contradicts published data, according to which the tensile stresses in most cases are formed in the joint region owing to the reaction of the material of a heat-affected region to dilatation of the material of a welded joint upon cooling. Compressive residual stresses in the material of a weld joint of rail steel are formed because of the positive volumetric effect of the γ → α transformation. In the surface layer of stellite cladding, tensile stresses of more than 700 MPa are detected. At the same time, residual stresses are absent at a depth of 100–120 μm, which indicates the formation of compressive stresses in the inner part of this layer that compensate tensile stresses in the external sublayer.

Measuring Nonequibiaxial Residual Stresses and Mechanical Properties Using Knoop Indentation

Abstract A proper knowledge of the mechanical properties and residual stresses of materials has a significant role in the prediction of engineering failures. Indentation is a simple, nondestructive test that is capable of estimating both residual stresses and mechanical properties. In frequent studies, the response of materials during the indentation process has been used as a key parameter to distinguish different substances. Here, a state-of-the-art method with no undesirable restriction is suggested to attain the work hardening exponent, yield strength, and planar nonequibiaxial residual stresses. In the current work, an extensive series of Knoop indentation simulations were performed using two indenter angles. Subsequently, a precise observation was made in order to find existent relationships. A local method was employed based on characteristics of similar materials to obtain stress-free sample parameters through a genetic algorithm, and then another error function was defined in order to measure the yield strength and work hardening exponent. After the determination of the mechanical properties and the stress-free sample’s parameters, a particular and precise categorization was made. Then, neural network analysis was employed to derive planar residual stresses. Experimental validation was conducted using six types of aluminum and steel specimens. The results confirmed a good agreement between the test data and those predicted using the suggested procedure.

In-Situ High-Energy X-ray Diffraction During a Linear Deposition of 308 Stainless Steel via Wire Arc Additive Manufacture

Adoption of metal additive manufacturing (AM) components in property-critical applications requires predictable performance of fabricated metal AM parts. In-situ diagnostics coupled with material models provide a pathway for qualification of AM whereby a prime objective is to capture data that inform or validate models or theory. Part of this is to understand the solidification and cooling of the material through diagnostics in order to ensure the part is being built correctly and that microstructures and properties are predictable. We have utilized high-energy X-ray diffraction to provide a unique probe for bulk material characterization in-situ during additive manufacture. The current work is focused on presenting the opportunities and potential pitfalls associated with extracting microstructural information from diffraction data that is necessarily limited due to the dynamic nature of the process. We present diffraction measurements and Rietveld refinement of stainless steel wire-arc line depositions using 71 keV X-rays, providing information on temperature, phase evolution, and residual stress during the deposition of a single-layer of 308L stainless filler wire on a 304L stainless steel substrate. In addition to observing both the liquid/solid and solid-state phase transformations, this methodology can be used to map the extent of the melt pool, identify thermal gradients, and measure residual stresses in materials during deposition.

Merenje zaostalih napona bez razaranja u konstrukcionim delovima mostova

Bridges are vital in our society for uninterrupted transportation of goods and people on roads and railways and timely maintenance and repair of bridges are of outmost importance. The residual stresses have a significant effect on the process of the initiation and propagation of the fatigue cracks in welded elements and are responsible for many bridge failures.Knowledge of residual stresses, their distribution and their nature is, therefore, of paramount importance in all stages of bridge's design, building and maintenance. Among nondestructive methods for residual stress measurements the use of ultrasonic waves is gaining popularity and acceptance. A portable instrument, UltraMARS that is capable of measuring residual stresses in materials either averaged through thickness or in surface and subsurface layers using ultrasonic waves of different frequencies and displaying the results in a form of a continuous curve on the screen of the instrument was developed and used successfully in many investigations [1, 2]. The main principles of operation and used methodology are briefly discussed, with actual measurement examples using the bulk, the surface and the subsurface presented. A new transducer for measurement of surface and subsurface stresses with a variable base between the ultrasonic wave sender and receiver was designed and manufactured recently. By changing the distance between the sender and receiver it is possible to obtain nondestructively information on residual stress distribution through a certain range of thicknesses of the interrogated materials and structures. Results of calibration of the new variable base ultrasonic transducer (VBUT) for a number of selected materials will be presented. The results of residual stresses measured in structural details of a bridge that was damaged as well as in a number of welded bridges before and after application of improvement treatment used to beneficially redistribute the residual stresses are also presented. The obtained data on residuals stress distribution had proven that the nondestructive ultrasonic method for measurement of residual stresses is a practical and useful tool in maintenance and repair of bridges.

Optical sensitivity enhancement in grating based micromechanical accelerometer by reducing non-parallelism error.

We report on optical sensitivity enhancement in a grating-based micromechanical accelerometer, which was achieved by reducing the non-parallelism error between the grating and reflected mirror. Based on the multi-slit Fraunhofer diffraction theory, an equivalent optical model is proposed in order to discuss the non-parallelism induced error that is caused by the residual stress in material and fabrication. An integrated fabrication flow with optimized quartz based and silicon based procedure is then presented to improve the parallelism between the grating and mirror, and to realize a hermetic package using silicon islands for the electrical interconnection. We experimentally characterize accelerometers' behavior by an interferometric beam detecting setup, which reveals the acceleration measurement with a scale factor improvement, noise floor decrease, and thus a bias stability enhancement from 2 mg to 0.35 mg (20 seconds interval, 1 g = 9.8 m/s2).

The effects of residual stress on elastic-plastic fracture propagation and stability

Residual stresses in materials affect their resistance to the initiation of fracture and to subsequent crack growth. Using full-field strain measurements and finite element analysis we demonstrate that the effect of residual stress on a material's crack growth resistance curve can be understood using elastic-plastic fracture mechanics. It is shown that Lei's modified J-integral formulation (Jmod) is a good predictor of the load vs crack extension behaviour of an elastic-plastic material containing residual stresses.

Corrosion behavior of severely plastic deformed magnesium based alloys: A review

The purpose of this paper is to provide an overview of the impact of the microstructural modifications via severe plastic deformation on the corrosion behavior of magnesium and its alloys, especially when they are considered to be biodegradable materials. Mechanical processing involved in grain refinement modifies textures and residual stresses of materials which have their own impacts on corrosion behavior as reported in a large number of studies. However, the existing literature on the influence of microstructure on corrosion resistance is often contradictory, which discloses a lack of knowledge in this area. In this article the effects and contributions of critical factors such as the grain size, texture, residual stress and second phase distribution, affected by severe plastic deformation, on the magne-sium corrosion behavior is reviewed in order to find a relation between the microstructure and corrosion resistance.

Experimental Investigation on the Fatigue Life of Ti-6Al-4V Treated by Vibratory Stress Relief

Vibratory stress relief (VSR) is a highly efficient and low-energy consumption method to relieve and homogenize residual stresses in materials. Thus, the effect of VSR on the fatigue life should be determined. Standard fatigue specimens are fabricated to investigate the fatigue life of Ti-6Al-4V titanium alloy treated by VSR. The dynamic stresses generated under different VSR amplitudes are measured, and then the relationship between the dynamic stress and vibration amplitude is obtained. Different specimen groups are subjected to VSRs with different amplitudes and annealing treatment with typical process parameters. Residual stresses are measured to evaluate the stress relieving effects. Finally, the fatigue behavior under different states is determined by uniaxial tension–compression fatigue experiments. Results show that VSR and annealing treatment have negative effects on the fatigue life of Ti-6Al-4V. The fatigue life is decreased with the increase in VSR amplitude. When the VSR amplitude is less than 0.1 mm, the decrease in fatigue limit is less than 2%. Compared with specimens without VSR or annealing treatment, the fatigue limit of the specimens treated by VSR with 0.2 mm amplitude and annealing treatment decreases by 10.60% and 8.52%, respectively. Although the stress relieving effect is better, high amplitude VSR will lead to the decrease of Ti-6Al-4V fatigue life due to the defects generated during vibration. Low amplitude VSR can effectively relieve the stress with little decrease in fatigue life.

Neutron Spectrometer Used for Nondestructive Detection of Materials Deep Stress: Status of the Project

The difficulty of materials inner stress detection is a barrier to engineering equipment research. And neutron scattering techniques is now recognized as the most precise method for mapping of inner residual stresses in materials or even components. Nine neutron scattering spectrometers of China Advanced Research Reactor (CARR) has been carried out thermal debugging, another five spectrometers are under construction. The thermal neutron spectrometer mentioned in this paper is one of the five spectrometers to be built in the neutron guide hall. It is anticipated that the instrument will be accomplished and available to users in 2018. The design of the hardware is mentioned. The function of positioning and control of the spectrometer can be carried out by the software. This spectrometer is available for material scientists to accomplish further studies with its function, and provides a good reference for spectrometer designing experts.

Ultrasonic Characterization of Residual Stress in Materials Based on Phase-frequency Relationship

Ultrasonic Characterization of Residual Stress in Materials Based on Phase-frequency Relationship

Imitational modeling of residual stresses in materials employed for the repair of structural steels

Results of the calculations of residual stresses of composites based on polymer binder and glass fiber, which are used in the repair of metal structures of machines, by imitational modeling have been considered. Imitational modeling has been carried out using a special program that enables one to calculate required parameters with a very high rate after choosing initial data from preformed number sets. It has been determined that the modulus of glass plastics has the most sizeable effect on residual stresses.