In order to determine the material constitutive model parameters of FGH4095 alloy treated by laser shock processing (LSP), the Johnson–Cook (J-C) plasticity model was selected. The strain hardening ...function parameters A, B and n can be determined form true plastic strain-stress curve. In this work, the engineering stress–strain stress curve was obtained from China Superalloys Handbook, which was converted into a true strain-stress curve, and then the elastic part of this curve was removed to obtain the equivalent plastic stress–strain. Parameter A is the initial yield stress in true plastic stress–strain curve, parameter B and n were determined by least square method of f1(ɛ)=A+Bɛn in the true plastic stress–strain curve. For the determination of parameter C, a method based on LSP experiment and LSP numerical simulation was proposed. We assumed the initial predicted value of parameter C is 0.0015, and then the numerical simulation work was undertook with the change of predicted value of parameter C until the error of the maximum compressive residual stress obtained by experiment and simulation falling into allowable range (±1%), and then the parameter C was determined. At the end, the J-C plasticity model parameters of FGH4095 alloy with A = 1057 MPa, B = 1420 MPa, n = 0.3625 and C = 0.011 were determined, which has important reference value and guiding significance for researchers to carry out the LSP numerical simulation work.
The similarity property of conformal parameterization makes it able to locally preserve the shapes between a surface and its parameter domain, as opposed to common parameterization methods. A ...parametric tool path planning method is proposed in this paper through such parameterization of triangular meshes which is furthermore based on the geodesic on meshes. The parameterization has the properties of local similarity and free boundary which are exploited to simplify the formulas for computing path parameters, which play a fundamentally important role in tool path planning, and keep the path boundary-conformed and smooth. Experimental results are given to illustrate the effectiveness of the proposed methods, as well as the error analysis.
Laser shock peening (LSP) is a novel metal surface modifying technology, which can enhance the mechanical properties of materials and extend fatigue performance of components evidently. The ...outstanding mechanical properties induced by LSP occurs through severe plastic deformation, which will cause the surface topography evolution. With the rapid development of artificial intelligence (AI), which provide an effective solution to solve complex problems when with limited experimental data. In this work, FGH4095 superalloy was selected as the experimental material. LSP experiments were conducted with a Q-switched Nd: YAG laser. Laser energy of 4 J, 6 J and 8 J were used with overlap rate of 30 % and 50 %. The residual stress, microhardness and surface topography of experimental samples treated by LSP was investigated. What is more, the AI method based on XGBoost was applied to predict the mechanical properties and surface roughness of FGH4095 treated by LSP. The laser energy, overlap rate, depth were set as input parameters, while the residual stress, microhardness and surface roughness were set as output parameters. The predicted results showed a great agreement with the experimental data. It can be indicated that XGBoost is a suitable method for accurately performing prediction of mechanical properties and surface roughness of materials treated by LSP.
•Single point laser shock peening for the single crystal superalloy.•The relationship of plastic deformation degree, surface microhardness and surface residual stress with laser pulse energy.•The ...convex structure and crater shape defect structures on the bottom surface.
The single crystal superalloy SRR99 experimental samples were single point treated by laser shock peening (LSP) with laser pulse energy of 5–7 J. The surface morphology, micro-hardness, surface residual stress and surface microstructure of samples prior and after LSP were determined by corresponding characterization instrument. From the surface morphology, a circular pit was formed in surface, which due to the severe plastic deformation induced by LSP, and the diameter & maximum relative height of circular pit were increase with laser pulse energy. From the micro-hardness and residual stress test results of samples, these were increased after LSP treatment. In detail, the initial microhardness and residual stress were 398 HV and -498 MPa, with laser pulse energy of 5 J, the microhardness and residual stress were increased to 455 HV and -843 MPa, when the laser pulse energy was increased to 7 J, the microhardness and residual stress were increased to 512 HV and -942 MPa. In addition, the surface roughness of samples was increased too, which reflect the severe plastic deformation. By observing the microscopic morphology of the bottom of the pit, it is found that there are convex structure and crater shape defect structures on the bottom surface, and the formation of these structures may affect the surface roughness of the shock area. Although LSP caused certain degree of twist deformation of the shape of the γ' phase, the original strengthening method characteristics of the matrix phase and strengthening phase was not destroyed, which still maintained the creep strength and thermal fatigue properties of superalloy. The experiment show that LSP can cause significant work hardening effect on the surface of superalloy, and the generated high residual compressive stress can effectively delay the initiation and propagation of cracks. Therefore, LSP technology can effectively improve the fatigue life of single crystal blade components.
A modified constitutive model, combining laser shock processing and dynamic strain aging (DSA), is used to obtain the compressive residual stress field of In 718 in warm laser shock processing (WLSP) ...by ABAQUS VUMAT subroutine. In this work, a constitutive model with DSA is simplified by a single equation to integrate the interactions of face-centered cubic (FCC) and body-centered cubic (BCC) crystal structure. The modified Voyiadjis–Abed–Song (VAS) constitutive model is imported by a procedure code developed independently, including the Mises yield criterion application and parameter update. Based on the constitutive model and Gaussian mode laser wave, the strengthen process of WLSP in In 718 is simulated. For the experiment, 30
×
30
×
4 mm In718 specimen is strengthened by WLSP without coating. We analyze the amplitude and distribution of residual stress to explore the effect of temperature in impact regions through experiment and simulation. Predicted by the modified VAS constitutive model, the residual stress predicted by the modified VAS constitutive model agrees well with the experimental data at various temperatures. As a result, temperature softening has obvious effect on the residual stress distribution for In 718 in WLSP at 200
°
C. At 300
°
C, the residual stress amplitude has no diminution compared with 200
°
C due to DSA active, even there is thermal softening. DSA promotes the diffused solute atoms gathering and dislocation multiplication, that makes a flow stress reduce at a temperature range.
K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by ...laser metal deposition shaping to control the cracking behaviour in laser metal deposition of K465 superalloy. The microstructure differences between the K465 superalloy with cracking and the laminated material were discussed. The microstructure and intermetallic phases were analyzed through scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the microstructure of K465/Stellite-6 laminated material samples consisted of continuous dendrites with a similar structure size in different alloy deposition layers, and the second dendrite arm spacing was finer compared with laser metal deposition shaping K465. The intermetallic phases in the different alloy deposition layers varied, and the volume fraction of carbides in K465 deposition layer of the laminated material was higher than only K465 deposition under the fluid flow effect. In addition, the composition and microhardness distribution of laminated materials variation occurred along the deposition direction.
Water-jet guided laser (WJGL) machining is a novel processing technology using water beam fibers to guide the laser to machine the work-piece surface. This processing technology has the advantage of ...almost no mi-cro-cracks, small heat-affected zone, pollution-free, less recast layer, high processing accuracy, parallel cuffing, etc. This work aims to investigate the effect of different WGLM parameters on the micro-morphology of materials and the mechanism between lasers and materials. The experiments for slotting and grooving 316L stainless steel thin samples were used by the WGLM system developed by our research group in this work. The 2D micro-topography after experiments were tested by the Zeiss Vert.A1 metalloscope, and the 3D micro-topography of samples after experiments were tested by the Leica DVM6 optical microscope with the large depth of field & Bruke Contour Elite I white-light interferometer. Experimental results show that a certain width deposition layer can be occurred in the machining region, an
In order to overcome the existing disadvantages of offline laser shock peening detection methods, an online detection method based on acoustic wave signals energy is provided. During the laser shock ...peening, an acoustic emission sensor at a defined position is used to collect the acoustic wave signals that propagate in the air. The acoustic wave signal is sampled, stored, digitally filtered and analyzed by the online laser shock peening detection system. Then the system gets the acoustic wave signal energy to measure the quality of the laser shock peening by establishing the correspondence between the acoustic wave signal energy and the laser pulse energy. The surface residual stresses of the samples are measured by X-ray stress analysis instrument to verify the reliability. The results show that both the surface residual stress and acoustic wave signal energy are increased with the laser pulse energy, and their growth trends are consistent. Finally, the empirical formula between the surface residual stress and the acoustic wave signal energy is established by the cubic equation fitting, which will provide a theoretical basis for the real-time online detection of laser shock peening.
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