Residual Stress Test Research Articles

Effect of laser remelting on microstructure and immersion corrosion of cold–sprayed aluminum coating on S355 structural steel

A cold–sprayed aluminum (Al) coating was processed on S355 structural steel using a laser remelting (LR). The surface and interface morphologies, chemical composition, and phases of obtained Al coating were analyzed using a field emission scanning electronic microscope (FESEM), energy dispersive spectrometer (EDS) and X–ray diffractometer (XRD), respectively, and its residual stress was analyzed using a X–ray diffraction residual stress tester. The corrosion behavior of Al coating was investigated using an immersion corrosion test, in 3.5% NaCl solution for 720 h, the electrochemical corrosion was tested on a PS268A type of electrochemical workstation, and the mechanism of LR on the corrosion behavior of Al coating was also discussed. The results show that the porosity on the cold–sprayed Al coating reduced and its compactness increased after LR, the phase of Al coating after LR is composed of Al, with no other oxides. The residual compressive stress of cold–sprayed Al coating after LR is −69.0 MP, increased by 25% than the cold–sprayed Al coating, improving its bonding strength. The corrosion potential of cold–sprayed Al coating after LR shifts positively, showing that the electrochemical corrosion resistance of cold–sprayed Al coating is improved after LR.

Improvement in fatigue properties of 2024-T351 aluminum alloy subjected to cryogenic treatment and laser peening

The aim of this study was to investigate the effects of Cryogenic Treatment (CT) and Laser Peening (LP) on the fatigue properties of 2024-T351 aluminum alloy. The measurements of tensile properties and microhardness were carried out, and the residual stress tests were also conducted through x-ray diffraction (XRD) technology. Examination of microstructure was executed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Fatigue tests were conducted and the fatigue fracture morphologies were also analyzed by SEM. Experimental results found that both CT and LP could enhance the fatigue properties of 2024-T351 aluminum alloy. The process of CT prior to LP could provide a higher fatigue life compared with single CT or LP process. After CT prior to LP, the fatigue life of the treated specimen was 28,077 cycles under gradient loading, which obtained an increase of 4640 cycles compared to the untreated specimen. Meanwhile, compared with single CT and LP, CT prior to LP could produce finer grains, more precipitated second phases, higher density dislocation and compressive residual stresses. Beneficial microstructure evolution and compressive residual stress induced by CT prior to LP were considered to be the main factors that contribute to the improvement of the fatigue properties.

Effects of laser shock peening on mechanical behaviors and microstructural evolution of brass

The mechanical behaviors and the microstructures of brass induced by laser shock peening (LSP) are investigated systematically. The compressive residual stresses (CRS) and the micro-hardness in surface layers are performed using X-ray residual stress tester and hardness tester respectively. The microstructures of the deformation layers are characterized using transmission electron microscopy (TEM). It is found that the CRS and the micro-hardness increasing are accompanied by improving laser pulse energy. The deformation layer induced by 4.5J LSP is divided into top surface layer, SPD layer and MPD layer according to the microstructures and CRS. The equiaxed grain size in the top surface layer after 4.5J LSP impacts is approximately 20 nm to 30 nm. The grain refinement process during LSP impacts can be described as follows: (i) dislocation structures are generated by strain and strain rate induced laser shock wave; (ii) original coarse grains subdivide into sub-grains with dislocation tangles (DTs) and dense dislocation walls (DDWs) forming at their grain boundaries; (iii) dynamic recrystallization (DRX) in sub-grain boundaries takes place due to the dislocation array transitions; (iv) new grain boundaries are formed in sub-grains, then they are subdivided into nano-scale equiaxed grains with the accumulation of plastic deformation.

Use of Plastic Correction Formula to Improve Accuracy of Welding Residual Stress Test with Blind-Hole Method

The blind-hole method is the most widely used approach to experimentally determine the distribution of residual stress. This paper aims to improve test accuracy of welding residual stress and conducts an experimental study on the strain release factors involved when using the blind-hole method for Q235 and Q345, two steels commonly used in building structures. The ranges of strain release factors A and B in the elastic stage, the effects of strain release factors on residual stress calculated values, and the plastic corrected strain release factors are analyzed considering of the effect of plastic deformation around the blind hole on measurement accuracy. Finally, a simplified calculation formula to determine strain release factors is proposed for use with the blind-hole method. Results show that in the elastic stage, strain release factor A for Q235 and Q345 ranges from −0.399 to −0.525 and strain release factor B from −0.791 to −0.960. Changing the strain release factors A and B shows that calculated residual tensile stress varies in relation to a decrease in both factor values. However, there is a increase in calculated residual compressive stress with a decrease in the strain release factor A value, but there is an decrease with a decrease in strain release factor B value. Calculated residual stress applied to elastic strain release factors is compared with that applied to amended plastic strain release factors for Q235 steel. The maximum deviation between calculated residual stress and test stress is reduced from 21.1 to 1.0%, and for Q345 steel from 26.5 to 1.2%. It is thus evident that the plastic correction formula proposed in this paper can be used in calculations when conducting a residual stress test.

Influence of the phase composition and microstructure of plasma cladding Fe-Cr-Ni-C alloy coating on residual stress and crack formation

The Fe–Cr–Ni–C alloy coatings with different phases have been prepared by plasma cladding technique on high manganese austenitic steel preheated with different temperatures. The effect of the phase composition on crack formation, residual stress, and micro-hardness of Fe–Cr–Ni–C alloy coatings was investigated by scanning electron microscopy (SEM) with energy-dispersive spectrum (EDS), micro-hardness tester, infrared thermal imager, and residual stress tester. The results show that for Fe-based coating deposited on the substrate non-preheated, the transverse and perpendicular cracks are generated after the end of cladding, which belongs to transcrystalline fracture. The Fe–Cr–Ni–C alloy coatings are composed of the solid solution of austenitic and fishbone-like eutectic carbide, which was mainly (Cr, Fe)7C3. As the preheating temperature of substrate is 350 °C, granular metallic carbides with the diameter 1 μm are precipitated at grain boundaries and no cracks formed. The carbide phases are mainly (Cr, Fe)7C3 and (Cr, Fe)23C6 in cladding coatings. With the decreased rate of cooling, carbide precipitation phase changed from metastable (Cr, Fe)7C3 to stable (Cr, Fe)23C6 phase. The precipitation stable carbide phase has significance to prevent the formation of cracks and improves the micro-hardness of the Fe-based coating on the substrate preheated to 350 °C. The residual stress of specimen with substrates of non-preheating and preheating 250 and 350 °C is 234.2, 267.3, and 300.6 MPa, respectively. The maximum value of micro-hardness of coating with substrates of non-preheating is 986.1 HV, which is about six times than that of substrate.

Study on the adhesive mechanism between the Ga doped ZnO thin film and the polycarbonate substrate

The Ga doped ZnO (GZO) film was deposited on the polymer substrate at room temperature by magnetron sputtering. The resistivity is 8.9×10−4Ωcm. The average transmittance in the visible region is over 85%. According to the resistivity and transmittance in the visible light, it is obtained that the film exhibits excellent electrical and optical properties, which satisfies the application for optoelectronic devices. However, the adhesion between the film and the polymer substrate is very weak. In order to figure out the reason of the weak adhesion, we study the adhesive mechanism between the GZO film and the polymer substrate through using depth profiling XPS method, residual stress test, and SIMS method for the first time. The residual stress of the film is a compressive stress. According to the SIMS results, an element diffusion exists at the interface. However, according to the depth profiling XPS results, there is no chemical bonding between the GZO film and the polymer substrate.

Correlation between the duty cycle and the surface characteristics for the nanostructured titanium aluminum nitride coating deposited by pulsed-DC PACVD technique

Abstract The purpose of this paper is to investigate the relation between duty cycle, microstructure and surface properties of the nanostructured titanium-aluminum nitride (TiAlN) coatings produced by using pulsed-DC plasma-assisted chemical vapor deposition (PACVD). In order to evaluate the effects of duty cycle, TiAlN coatings were applied for 150 min in the 30, 40, and 50% of duty cycle at 470 °C substrate temperature, 10 kHz frequency, and 3 mbar working pressure. Field emission-scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and Energy-dispersive X-ray spectroscopy (EDS) were used for the coatings characterization. To evaluate the coatings surface properties, Nano-indentation, residual stress tester, Tafel polarization, and electrochemical impedance spectroscopy (EIS) were also utilized. The results implied that microstructure and mechanical properties of the coating have a significant correlation with duty cycle. Due to the fact that nucleation and growth occurs in the off-time, with decrease in duty cycle, the number of nuclei significantly increases. So, when duty cycle declined from 50 to 30%, coating nano-hardness increased from 26 to 31 GPa. Furthermore, corrosion behavior showed that the polarization resistance of the coating deposited at 30% duty cycle, is the highest value in complete accordance with the obtained results from tafel polarization curves (the least corrosion current density).

Influence of Processing Parameters on Injection Molded Polystyrene Using Taguchi Method as Design of Experiment

The influence of processing parameters onto the tensile properties, which also indicating the failure rate indirectly, of injection molded polystyrene (PS) was investigated. Dumbbell samples were being molded and tested for tensile properties by using Taguchi method as a robust design of experiment. The tensile properties of PS samples were analyzed accordingly and showed that the introduction of weld line, polymer melt temperature and the mold temperature were among the parameters of significant effect onto the strength of PS samples, where the introduction of weld line giving the most influence on material strength. Heat reversion showed that the change in material strength was due to the difference in residual stress and Ubbelohde testing showed that thermal degradation was minimal and had little effect on the material strength. The CADMOULD simulated results showed that the effects of processing parameters were not that great and was due to the software treat samples with and without weld line very differently.

Improvement of abrasion resistance in artificial seawater and corrosion resistance in NaCl solution of 7075 aluminum alloy processed by laser shock peening

As 7075 aluminum alloy is widely used in a humid environment, in order to enhance its abrasion resistance and electrochemical corrosion resistance, the paper studied the effect of laser shock peening on abrasion resistance in artificial seawater and corrosion resistance in 3.5% NaCl solution of 7075 aluminum alloy. Result shows that when specimens were treated once and twice with 7.17GW/cm2 the abrasion loss would be reduced by 43.75% and 46.09% compare to untreated respectively, and the corrosion rate of 7075 aluminum alloy could be reduced as much as 50.32% by LSP treatment with 7.17GW/cm2. What’s more, the effects on the microhardness, microstructure and residual stress with different LSP impacts and power density were investigated to find out strengthening mechanism of laser shock peening, which were observed and measured by microhardness tester, optical microscope and X-ray diffraction (XRD) residual stress tester. In the entire laboratory tests, it is considered that LSP is a practical option to improve abrasion resistance in seawater and corrosion resistance of 7075 aluminum alloy.

Non-destructive testing of residual stresses by magnetic methods under conditions of simple stressing

We have shown how crucial it is to determine the residual stresses (RS) at the stages of the product life cycle by means of the non-destructive testing (NDT) magnetic methods and to create computational algorithms and models. The experimental results of the RS in rod-shaped specimens after the 3-point-bending by magnetic-noise analysis and coercive force measurement are proved as being topical. The interrelations between the value of the change undergone by magnetic characteristics that are measured by the NDT magnetic methods and the value of the axial RS resulted from modeling by finite element method are revealed.

Contact Laser-Ultrasonic Evaluation of Residual Stress

Investigation of residual stresses in an infrastructure is important due to the reason of safety. One of the most important problems is non-destructive testing of residual stresses particularly in welded constructions. A quite lot of technologies are used to solve this problem. Ultrasonic testing is based on the dependence of the velocity of ultrasonic waves on the stress value within a material under study. This technology is robust, operative and can be used in field conditions. The main problem is to measure the velocity of ultrasonic waves with high precision at a short trace. The proposed technique of the Contact Laser-Ultrasonic Evaluation (CLUE) is used in our work to overcome this difficulty. The variation of the results of the measurement of the ultrasonic wave velocity using CLUE does not exceed 0.05% and provides the threshold of the detection of the residual stress in steel at the level of 2-3 MPa. Basics of CLUE and some experimental cases of the study of the uniaxial stress in compressed and tensioned rail steel specimens are described. The advantages and disadvantages of CLUE for the stress measurement are discussed.

Superficial Residual Stresses in Face-Milling the 17-4PH Stainless Steel at Various Feed Rates

17-4PH stainless steel is a widely used martensitic precipitation hardening stainless steel, and it is a typical difficult-to-cut material. Residual stress is an important part of the surface integrity. In this paper, superficial residual stress tests of face-milling the 17-4PH stainless steel were carried out at 0.1~0.3 mm/tooth with TiAlN coated carbide inserts. The effects of feed rate on the superficial residual stresses at various cutting speeds were studied. It was found that the residual stresses on the machined surface were very sensitive to the feed rate. The superficial residual stresses at the directions of parallel to and normal to the feed direction both remained compressive and changed obviously in higher compressive direction along with the feed rate. The burnishing effect determined by the cutting force was found to be the primary reason of the residual compressive stresses on the machined surface. The suitable cutting parameters were recommended according to the superficial residual stresses.

Microstructure and Residual Stress Distributions Under the Influence of Welding Speed in Friction Stir Welded 2024 Aluminum Alloy

Friction stir welding was conducted on 8-mm-thick plates made of AA2024-T351 aluminum alloy at tool traverse speeds between 8 and 31.5 mm/minutes and tool rotational speed between 400 and 800 rpm. Metallographic analyses and mechanical tests including hardness, tensile, residual stress, and fracture toughness tests were carried out to evaluate the microstructural and mechanical properties of the joints as a function of the process parameters. The finite element simulation of the FSW process was also performed using a thermal model. The hardness test results show that the increase in rotational speed or decrease in traverse speed of the tool would cause a decrease in weld zone hardness. The best tensile properties are obtained at rotational/traverse speed ratio between 20 and 32. Also, the longitudinal residual stress profiles were evaluated by employing X-ray diffraction method. The numerical and experimental results showed that the increase in a traverse or rotational speed would increase the residual stress of the weld zone. From the fracture toughness results, it was found that the welding process decreases the joints fracture toughness 18 to 49 pct with respect to the base metal.

Test study on residual stress distribution of hybrid steel u-rib stiffened plates

Orthotropic steel bridges were found to experience early fatigue failures of several welded connections in the steel deck plate. The welding process inevitably produces welding residual stresses and deformations that should be evaluated and considered to better understand the fatigue life of steel bridges. Aiming to study the residual stress distribution of hybrid steel u-rib stiffened plates, the blind hole method was applied. Various parameters, including the plate widths, the ratio of the u-rib thickness to the motherboard thickness, and the steel strength of the combination of the u-rib with the motherboard, were considered, and nine specimens were subjected to experimental tests. The results indicate that strain release factors have great impact on the calculated residual stress: as the value of strain release factor increases, the calculated residual stress in absolute term increases accordingly. However, due to experimental errors, as the ratio of the motherboard to the u-rib thickness varies from 1:2 to 1:2.5 and the u-rib spacing increases from 120mm to 160mm, the residual stress value and the distribution change are not obvious; when different steel strengths were used in the specimens, as the material yield strength of the motherboard (u-rib) increases, the residual tensile stress peaks of the motherboard (u-rib) increase, while the residual tensile stress distribution of the u-rib (motherboard) remains essentially the same. Based on the comparison between the cutting method and the blind hole method, the values from residual stress test points appear to be similar; from the perspective of measuring points' distribution and the directions of the tested residual stress, the cutting method cannot test the weld location, and the residual stress at the measuring point can only be obtained along the cutting direction because the blind hole method can test the weld location residual stress, and the residual stress of the measuring point can be obtained in any direction.

INTERFACE DEVICE FOR NONDESTRUCTIVE TESTING OF RESIDUAL SURFACE STRESSES

The paper considers the organization of connection of a personal computer with a device for nondestructive testing of residual surface stresses. The device works is based on the phenomenon of diffraction of ionizing radiation from the crystal lattice near the surface of the crystallites. Proposed software interface to the organization for each type of user: the device developers, administrators, users. Some aspects of the organization of communication microcontroller to a PC via USB-port

Nondestructive Testing of Residual Stress on the Welded Part of Butt-welded A36 Plates Using Electronic Speckle Pattern Interferometry

Most manufacturing processes, including welding, create residual stresses. Residual stresses can reduce material strength and cause fractures. For estimating the reliability and aging of a welded structure, residual stresses should be evaluated as precisely as possible. Optical techniques such as holographic interferometry, electronic speckle pattern interferometry (ESPI), Moire interferometry, and shearography are noncontact means of measuring residual stresses. Among optical techniques, ESPI is typically used as a nondestructive measurement technique of in-plane displacement, such as stress and strain, and out-of-plane displacement, such as vibration and bending. In this study, ESPI was used to measure the residual stress on the welded part of butt-welded American Society for Testing and Materials (ASTM) A36 specimens with CO₂ welding. Four types of specimens, base metal specimen (BSP), tensile specimen including welded part (TSP), compression specimen including welded part (CSP), and annealed tensile specimen including welded part (ATSP), were tested. BSP was used to obtain the elastic modulus of a base metal. TSP and CSP were used to compare residual stresses under tensile and compressive loading conditions. ATSP was used to confirm the effect of heat treatment. Residual stresses on the welded parts of specimens were obtained from the phase map images obtained by ESPI. The results confirmed that residual stresses of welded parts can be measured by ESPI.

Numerical modeling and experimental identification of residual stresses in hot-rolled strips

The problem of calculations and experimental validation of residual stresses in hot-rolled strips is considered in the paper. Residual stresses become of practical importance when the laser cutting of strips is applied. The goal of this paper is development and experimental validation of a model of residual stresses in hot-rolled strips based on the elastic–plastic material model. The models of elastic–plastic deformation during cooling of hot rolled strips during laminar cooling and in the coil were developed. Elastic–plastic properties of the material were determined experimentally using tests on GLEEBLE 3800. Industrial testing of residual stress in strips after cooling in coil was performed. For measurement of residual stress in strips the X-ray diffraction method was used.

Residual stress tests of welded Q690 high-strength steel box- and H-sections

Many studies on the experiment and simulation of residual stresses in mild carbon steel sections have been conducted. However, few investigations focus on Q690 high-strength steel sections. Because of the differences between high-strength steel and mild carbon steel in terms of stress–strain relationships and thermal properties of materials, it is necessary to investigate the residual stress in high-strength steel welded sections. In this study, three box- and H-sections fabricated from Q690 steel plates were employed for the measurement of residual stresses. The thickness of the sections with various dimensions was 16mm. This paper presents the magnitude and distribution of residual stresses in box- and H-sections made of Q690 steels. The simplified residual stress distribution models over box- and H-sections welded with Q690 steels are proposed. It is found that Q690 high-strength steel specimens possess lower ratios of residual compressive stress compared with that of Q460 steel specimens.

Residual stress distribution at grind-hardening layer surface of the 40Cr workpiece

Currently, good precision is established by the grinding process used for machining the parts. However, there are still uncontrollable steps to this process, such as the apparition of some damage, in which the major deterioration is from the residual stress. In order to investigate the residual stress caused by mechanical stress, thermal stress and phase transformation stress, using the grind-hardening test of 40Cr and the residual stress test, the residual stress distributions under different grinding parameters were obtained. In addition, numerical simulation for the thermal stress of the workpiece surface was carried out by ANSYS, and then the distribution of phase transformation stress under different grinding parameters was deduced. The research shows that grinding parameters have significant influence on the distribution of residual stress at the hardening layer.

In-situ Curing Strain Monitoring of a Flat Plate Residual Stress Specimen Using a Chopped Stand Mat Glass/Epoxy Composite as Test Material

The curing stresses in a newly proposed bi-axial residual stress testing configuration are studied using a chopped strand mat glass/epoxy specimen. In-situ monitoring of the curing is conducted using dielectric and fibre Bragg grating sensors. It is confirmed that a bi-axial residual stress state can be introduced in the specimens during curing and a quantification of its magnitude is presented. An alternative decomposition method used for converting the dielectric signal into a material state variable is proposed and good agreement with models found in the literature is obtained. From the cure cycles chosen it is suggested that any stress build up in the un-vitrified state is relaxed immediately and only stress build up in the vitrified state contributes to the residual stress state in the specimen.