Showing papers by "Southwest Wisconsin Technical College published in 2020"

Microstructures and Mechanical Properties of In-Situ Al 3 Ti/2024 Aluminum Matrix Composites Fabricated by Ultrasonic Treatment and Subsequent Squeeze Casting

Abstract: Squeeze casting is a near net shaping technology which is advantageous to refining the microstructures and improving the mechanical properties. In the present work, in-situ Al3Ti/2024 Aluminum matrix composites with different amount of Al3Ti reinforcements were successfully fabricated by ultrasonic treatment and subsequent squeeze casting. The effects of specific pressure and the amount of reinforcements on microstructures and mechanical properties were studied. The results show that when the specific pressure is increased from 0 to 150 MPa, the average grain sizes of α-Al matrix are decreased by 39.8%, and the yield strength and compressive strength are increased by 16.8% and 22.9%, respectively. However, severe segregations of eutectic structures were generated under an excessive specific pressure of 200 MPa, which also results in deterioration in the mechanical strength. The mass fraction of Al3Ti phases has significant influence on morphology of eutectic structures. When the mass fraction of Al3Ti phases is increased from 4 to 16 wt%, the eutectic structures was changed from continuous network to dispersed structures gradually. The compressive strength was increased from 611.2 to 712.0 MPa (increased by 16.5%), as the Al3Ti content increasing from 0 to 16 wt%. However, as the mass fraction of Al3Ti phases increased, the variation in the yield strength is not monotonically increasing.

Effect of texture types on microstructure evolution and mechanical properties of AZ31 magnesium alloy undergoing uniaxial tension deformation at room temperature

Abstract: Influence of texture type on mechanical properties and the evolution of microstructure and texture is thoroughly investigated via uniaxial tension experiment along rolling direction (RD) at room temperature on two different AZ31 alloy sheets. Electron backscattered diffraction (EBSD) measurements on deformed samples confirm that dislocation slip is the main deformation mechanism in as-received sheet with a typical basal texture, while dislocation slip and extension twinning (ET) both contribute to sustaining plastic strain in the sheet with a rare RD-split bimodal texture, which is fabricated by equal channel angular rolling and continuous bending process with subsequent annealing (ECAR-CB-A). Therefore, these two sheets demonstrate obviously different texture evolution during plastic deformation. As-received sheet maintains basal texture and further experience the concentration of basal poles towards normal direction (ND). However, ECAR-CB-A sheet not only undergoes the gradual diffusion and rotation of tilted basal poles to ND but also the development of a new TD-component texture. The activation of ET variants in ECAR-CB-A sheet is confirmed to play an important role in texture evolution, and the number of activated ET variants is increasing with the increase of angle between ND and c-axis. In addition, acquired mechanics data demonstrate that ECAR-CB-A sheet possesses higher fracture elongation (24%) and lower yield stress (73 MPa) as compared to as-received sample. This issue can be ascribed to the participation of ET to coordinate plastic deformation along c-axis and the easier activation of basal slip in ECAR-CB-A sheet.

Quantum image encryption algorithm based on bit-plane permutation and sine logistic map

Abstract: Quantum cryptography improves efficiency and security of image content protection owing to the characteristics of qubits. In this paper, a novel quantum image encryption algorithm based on bit-plane permutation and sine logistic map is presented. The image to be encrypted is firstly represented with novel enhanced quantum representation model and then the quantum Arnold transform is used to scramble pixel positions. The bit-plane cross-exclusive OR and shift operations are designed to change the pixel values. The final ciphertext image is obtained through a diffusion process utilizing sine logistic map, which extremely enlarges key space. The quantum circuits of each procedure are given. Simulation results and theoretical analysis verify that the proposed quantum image scheme has good performance in the aspect of security and the computational complexity is superior to its classical counterpart.

Assessment in predictability of visco-plastic self-consistent model with a minimum parameter approach: Numerical investigation of plastic deformation behavior of AZ31 magnesium alloy for various loading conditions

Abstract: By predicting the complex deformation mechanisms, visco-plastic self-consistent (VPSC) model has been found to be a useful tool for investigating plastic deformation behavior of magnesium alloy. The standard version of VPSC model involves a large number of adjustable parameters. Using independent arguments obtained from single tests, VPSC model with a minimum parameter approach immensely reduces the number of adjustable parameters, hence shows huge potential in simulating plastic deformation behavior of thin magnesium alloy sheet. The predictability of this new approach is thoroughly assessed in the present study. Although only the mechanical response of in-plane tension (IPT) in AZ31 magnesium alloy is applied to calibrated the corresponding material parameters, simulated results in terms of texture evolution using VPSC model with a minimum parameter approach show a relatively small difference by comparison with the predicted ones applying the standard version of VPSC model during IPT, in-plane compression (IPC), through-thickness compression (TTC), and plane strain compression (PSC), respectively. Furthermore, the corresponding activated deformation mechanisms during various deformation processes are further analyzed. With the exception of pyramidal slip, the predicted activities of remaining deformation mechanisms are generally consistent with each other. This phenomenon is identified to be the root of minor difference in texture evolution. Moreover, the predicted activities in pyramidal slip using VPSC model with a minimum parameter approach are relatively higher than the corresponding ones in the case with the standard version of VPSC model. However, these reported results are not beyond the maximum of published literature, and hence are acceptable when simulating various plastic deformation behavior of AZ31 magnesium alloy.

Enhanced protective nanoparticle-modified MgAl-LDHs coatings on titanium alloy

Abstract: Mg Al LDHs (layered double hydroxides) coatings were deposited on the surface of titanium alloy Ti10V2Fe3Al, accompanied by modification with ZrO2 and MoS2 nanoparticles through electrophoretic deposition. FE-SEM, XRD and EDS measurements were used to investigate the microstructure and composition of the composite coatings. Corrosion resistance was measured by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. The LDHs/MoS2 composite coating exhibited the best corrosion resistance. Ball on disc tests was implemented to obtain morphology, the friction coefficient and wear loss of the worn surfaces. The LDHs/ZrO2 composite coating exhibited the best wear resistance. A mechanism for enhancing the wear-resistance of the different nanoparticles-modified MgAl-LDHs coatings was proposed.

Surface evolution analysis of CrxWyNz coatings on WC mold in glass molding process

Abstract: The CrxWyNz coatings were synthesized on the cemented carbide (WC-8Co) by plasma-enhanced magnetron sputtering (PEMS). The detailed glass cylinder compression was tested for the molding performance of the coated molds in the precision glass molding machine (PGMM). This work examined the surface morphology evolution, elemental compositions and mechanical properties of the CrxWyNz coatings by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), nano-indentation tester and atomic force microscope (AFM). The results showed that with the increased W content in the CrxWyNz coatings, the nano-hardness and Young's modulus of the coatings increased, and the surface roughness of the coatings reduced. The contact zone had lower surface roughness than the non-contact zone because of inhibiting the oxidation reaction. The molded glass pressing on the surfaces of Cr27W24N49 and Cr18W28N54 coatings had relatively better light transmittance. Besides, the CrxWyNz coatings (18 ≤ x ≤ 27, and 24 ≤ y ≤ 28) exhibited better oxidation resistance, chemical inertness, and surface quality during thermal-mechanical cycles, more suitable for glass molding protective coatings. The work sheds light on the preparation and application of glass molding protective coatings.

Effect of annealing environment on the microstructure and mechanical property of CrWN glass molding coating

Abstract: The CrWN glass molding coating was synthesized by plasma enhanced magnetron sputtering (PEMS). The effect of annealing environment (e.g., vacuum, N2 and Air) on the microstructure and mechanical property of as-deposited coating was investigated by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM) and nanoindentation tests. Results showed that the as-deposited coating exhibited dense columnar structure consisting of multilayer CrN and W2N phases. The vacuum annealed coating showed similar thickness to that of as-deposited coating, but underwent visible surface coarsening because of slight oxygen erosion. The N2 and air annealed coatings suffered from varying degree of oxidation damage accompanied by the formation of mixed WO3-CrWO4 phases, which consequently resulted in severe thickness expansion and surface coarsening. The vacuum annealing induced a spinodal decomposition of supersaturated solid solution to form nm-sized CrN and W2N domains. Strain fields originating from the lattice mismatch eventually caused a pronounced age-hardening in the vacuum annealed coating. Whereas the N2 and air annealed coatings showed significant mechanical degradation because these loose WO3-CrWO4 oxides degraded the stable matrix structure. Our results clearly demonstrated that vacuum environment effectively suppressed the oxidation damage and mechanical degradation of glass molding coating.

Hot deformation behavior of 7A04 aluminum alloy at elevated temperature: constitutive modeling and verification

Abstract: The hot deformation behaviour of one 7XXX series aluminium alloy, 7A04, has been studied by conducting isothermal hot compression tests with degree of compression up to 55% at the temperature ranging from 350 °C to 480 °C and strain rates ranging from 0.002 s−1 to 20s−1. Based on characteristic of the flow stress obtained from those tests, an extended Voce equation, which constant parameters were modified as Arrhenius-type type equation, was given and used to calculate the flow stresses under the conditions of the hot deformation. The parameters of extended Voce equation were determined by experimental results. The comparison between the experimental and predicted flow stress values at the hot compression parameters range indicated good agreement. The average absolute relative error, root mean square error and the correlation coefficient were found to be 4.9%, 4.8 MPa and 0.997, respectively, which confirmed the extended Voce model had good accuracy. Additional, a finite element simulation model of isothermal hot compression process was used to verify the new Voce equation and the results verified the accuracy of the new equation. The main softening mechanism of the hot deformation was dynamic recovery and was confirmed by optical microstructures.

A nonlinear Wiener degradation model integrating degradation data under accelerated stresses and real operating environment

Abstract: Remaining useful life (RUL) prediction in real operating environment (ROE) plays an important role in condition-based maintenance. However, the life information in ROE is limited, especially for so...

Macro-alloying Effects of Al and Ag on the Age-Hardening Behavior and Precipitates Microstructure of a Mg-4Sn Alloy

Abstract: The effects of macro-alloying of Al and Ag on the age-hardening behavior and precipitates microstructure of a Mg-4Sn alloy aged at 160°C were investigated. All the alloys exhibited a similar hardening trend, and achieved the peak-aged state around 230 h. The peak-aged Mg-4Sn alloy contained several thin basal plates and a few Mg2Sn laths heterogeneously distributed within the matrix, which resulted in a poor hardening response. The Mg-4Sn-4Al alloy exhibited an improved age-hardening response by the enhanced precipitation process and an increased volume fraction of the Mg2Sn precipitates. An addition of 1.5 wt.% Ag to the ternary alloy significantly refined the Mg2Sn precipitates. In the peak-aged Mg-4Sn-4Al-1.5Ag alloy, Al and Ag solute atoms still supersaturated the α-Mg matrix, thus further improving the hardness by the solid-solution strengthening effect. Some Ag atoms segregated with the Mg2Sn precipitates, and minor Ag-enriched particles were also formed. In contrast, Al distributed more uniformly in the matrix.

Impact Characteristics and Fatigue Life Analysis of Multi-Wire Recoil Spring for Guns

Abstract: Recoil spring is a key part in automatic or semi-automatic weapons re-entry mechanism. Because the stranded wire helical spring (SWHS) has longer fatigue life than an ordinary single-wire cylindrically helical spring, it is often used as a recoil spring in various weapons. Due to the lack of in-depth research on the dynamic characteristics of the current multi-wire recoil spring in recoil and re-entry processes, the fatigue life analysis of the current multi-wire recoil spring usually only considers uniform loading and does not consider dynamic impact loads, which cannot meet modern design requirements. Therefore, this paper proposes a research method for fatigue life prediction analysis of multi-wire recoil spring. Firstly, based on the secondary development of UG, a three-wire recoil spring parameterized model for a gun is established. Secondly, ABAQUS is used to carry out a finite element analysis of its dynamic response characteristics under impact, and experimental verification is performed. Then, based on the stress-time history curve of the dangerous position obtained by finite element analysis, the rain flow counting method is used to obtain the fatigue stress spectrum of recoil spring. Finally, according to the Miner fatigue cumulative damage theory, the fatigue life prediction of the recoil spring based on the S-N curve of the material is compared with experimental results. The research results show that the recoil spring has obvious transient characteristics during the impact of the bolt carrier. The impact velocity is far greater than the propagation speed of the stress wave in the recoil spring, which easily causes the spring coils to squeeze each other. The maximum stress occurs at the fixed end of the spring. And the mean fatigue curve (50% survival rate) is used to predict the life of the recoil spring. The calculation result is 8.6% different from the experiment value, which proves that the method has certain reliability.

Microstructure and electromagnetic properties of Nd3+substitued Mg-Mn nanocrystalline ferrites via hydrothermal procedure

Abstract: Mg0.2Mn0.8NdxFe2-xO4 (x = 0.000, 0.025, 0.050, 0.075 and 0.010) nano crystalline is synthesized via hydrothermal technique. Single cubic spinel phase is confirmed by XRD and the formation of Mg0.2M...

Research on Vibration Prediction Method of Aircraft External Stores Based on Deep Belief Network

Abstract: This paper proposes a method for predicting the vibration environment of aircraft external stores based on deep belief network, which based on the relationship between the vibration environment, pressure altitude and Mach number of the aircraft external stores in flight. Firstly, GJB 150.16A empirical formulas were analyzed and then generating simulation data, which a total of 7470 sets. Secondly, linear regression and deep belief network models were set up respectively, and deep belief network number of hidden layer node was optimized, then the expected errors of two methods were compared and analyzed, including root mean square error (RMSE), mean absolute error (MAE) and mean relative error (MRE). Finally, DBN method was applied to a case for prediction the vibration of a certain aircraft store, intending to verify the feasibility and accuracy of DBN method. The results show that the DBN model can fully characterize the non-linear relationship between the pressure altitude, Mach number and RMS value of the aircraft external stores in the flight environment, and the overall expected effect is better than linear regression. The expected mean relative error is less than ± 3 dB. This method has provided a new way to predict the vibration environment of aircraft external stores, and is of great significance for PHM in the whole life of aviation weapon equipment.

Verification of Dislocation Density and Dynamic Recrystallization in Deformed Pure Copper

Abstract: The mechanisms of dynamic recovery and dynamic recrystallization significantly affect the mechanical behavior and microstructure of the materials deformed at high temperatures. The modified Kocks and Mecking (K–M) model was used to assess the evolution of dislocation density of pure copper under high-temperature compression. The relationship between the deformation conditions and model parameters was derived and verified. The model offers quantitative prediction of flow stress curves, a recrystallized fraction, and recrystallized grain size under different conditions. The model can well integrate the recrystallization mechanism during deformation. The dislocation density and dynamic recrystallization evolution of pure copper provide a basis for optimizing thermomechanical processing in different fields of industry.