Surface Shear Research Articles

Fundamental Properties and Clinical Application of 3D-Printed Bioglass Porcelain Fused to Metal Dental Restoration.

The purpose of this study is to evaluate the mechanical properties and clinical fitness of 3D-printed bioglass porcelain fused to metal (PFM) dental crowns. To evaluate the mechanical properties, tensile strength, Vickers microhardness, shear bond strength, and surface roughness tests of the SLM printed Co-Cr alloy was conducted. A right mandibular 1st molar tooth was prepared for a single dental crown (n = 10). For a three-unit metal crown and bridge, the right mandibular first premolar and first molar were prepared. Bioglass porcelain was fired to fabricate PFM dental restorations. A clinical gap was observed and measured during each of the four times porcelain was fired. A statistical analysis was conducted. The SLM technique showed the largest statistically significant tensile strength and a 0.2% yield strength value. The milling technique had the lowest statistically significant compressive strength value. The shear bond strength and surface roughness showed no statistically significant difference between the fabricated method. There was a statistically significant change in marginal discrepancy according to the porcelain firing step. The casting technique showed the greatest statistically significant margin discrepancy value. The SLM method showed better fitness than the traditional casting method and showed better mechanical properties as a dental material.

Dispersion of Shear Surface Waves in an Elastic Substrate Imperfectly Bonded with an Elastic Layer

Исследовано распространение поверхностной поперечной волны для слоистой структуры, состоящей из упругого слоя, лежащего на упругом полупространстве с поверхностью неполного упругого контакта. Рассмотрены две различные модели неполного упругого. Получены дисперсионные уравнения, описывающие зависимость фазовой скорости поверхностной волны от волнового числа. На основе анализа дисперсионных уравнений показано, что несовершенство границы раздела может существенно уменьшить или увеличить фазовую скорость поверхностной волны. Առաձգական կիսատարածության վրա գտնվող և թերի կոնտակտ ունեցող առաձգական շերտ բաղադրյալ կառուցվածքի համար ուսումնասիրված է մակերևութային լայնական ալիքի տարածումը: Դիտարկվել են թերի կոնտակտի երկու տարբեր մոդելներ: Ստացվել են դիսպերսիոն հավասարումներ, որոնք նկարագրում են մակերևութային ալիքի ֆազային արագության կախումը ալիքային թվից: Դիսպերսիոն հավասարումների հետազոտումով ցույց է տրվել, որ բաժանման եզրի անկատարությունը կարող է էապես մեծացնել, կամ փոքրացնել մակերևութային ալիքի ֆազային արագությունը: The surface shear wave is studied in layered bi-material structure consisting from an elastic layer lying on an elastic half-space with an imperfectly bonded interface. The two models of the imperfect “slip” and “scattering” interface are considered. The dispersion equations are obtained describing the surface wave phase speed versus wavenumber. Based on the analysis of dispersion equations it is shown that the interface imperfectness can sufficiently decrease in “slip” case or increase in “scattering” case the surface wave phase speed.

Study on the Effects of Different Water Content Rates on the Strength and Brittle Plasticity of Limestone

Water can deteriorate the compositional properties of rock through softening and dissolution. The water content rate of rock has a certain effect and can cause changes in rock properties caused by the water action. In this research, to study the effects of the water content rate on the strength and brittle plasticity of limestone, uniaxial compression tests with different water content rate states were conducted, and the form of limestone damage under different water content rate conditions was analyzed. The effects of the different water content rates on the modulus of elasticity, uniaxial compressive strength, brittleness index B value, and brittleness correction index BIM value (BIM: the ratio of dissipated strain energy to releasable elastic strain energy at the peak point of the specimen) of limestone were investigated. It was found that as the rate of water content in the limestone increased from 0% to 0.27%, the penetration shear surface on the limestone’s damaged surface decreased. The modulus of elasticity decreased from 8.85 to 6.76 GPa, the uniaxial compressive strength decreased from 74.11 to 57.60 MPa, the brittleness index B value decreased from 1.17 to 1.04, and the brittleness correction index BIM value increased from 0.09 to 0.26. As the rate of water content on the limestone increased, the rock’s modulus of elasticity and uniaxial compressive strength decreased. Additionally, the rock’s brittleness decreased, and the percentage of plastic deformation in the total deformation increased.

Shear behavior and damage evolution of the interface between rough rock and cemented tailings backfill

The shear behavior of the interface between rock and cemented tailings backfill (CTB) is extremely critical to the backfill design and stability of the backfilled underground mined-out areas. The corresponding shear behavior and surface damage can be significantly affected by the roughness of the rock surfaces. In our study, sandstone with the same rough surface were prepared using rock engraving technology. The direct shear tests on the rough rock-CTB interfaces were carried out under four different normal stresses and six different roughness of the rock surfaces. The interfacial shear strength and corresponding surface damage were analyzed. A new shear strength criterion of the rough rock-CTB interface was then proposed and verified. Our study shows that the compressive deformation of the combined specimen is much larger than that of dilatancy under a higher normal stress. The residual shear strength is less affected by the rock surface roughness under lower normal stress. The corresponding shear strength of the rough rock-CTB interface does not necessarily increase with the rock surface roughness due to the large strength difference between the sandstone and CTB. The interfacial damaged zones, which increase with the normal stress, are roughly concentrated in the larger concave section of the corresponding 2D profiles. The established shear strength criterion of the rock-CTB interface consists of basic mechanical and morphology parameters which can be easily estimated by the general laboratory tests. The findings obtained from this study can be used to quantify the effect of the rough rock-CTB interface on the stability of CTB.

A Cohesive-Zone-Based Contact Mechanics Analysis of Delamination in Homogeneous and Layered Half-Spaces Subjected to Normal and Shear Surface Tractions

AbstractA contact mechanics analysis of interfacial delamination in elastic and elastic-plastic homogeneous and layered half-spaces due to normal and shear surface tractions induced by indentation and sliding was performed using the finite element method. Surface separation at the delamination interface was controlled by a surface-based cohesive zone constitutive law. The instigation of interfacial delamination was determined by the critical separation distance of interface node pairs in mixed-mode loading based on a damage initiation criterion exemplified by a quadratic relation of the interfacial normal and shear tractions. Stiffness degradation was characterized by a linear relation of the interface cohesive strength and a scalar degradation parameter, which depended on the effective separation distances corresponding to the critical effective cohesive strength and the fully degraded stiffness, defined by a mixed-mode loading critical fracture energy criterion. Numerical solutions of the delamination profiles, the subsurface stress field, and the development of plasticity illuminated the effects of indentation depth and sliding distance on interfacial delamination in half-spaces with different elastic-plastic properties, interfacial cohesive strength, and layer thickness. Simulations yielded insight into the layer and substrate material property mismatch on interfacial delamination. A notable contribution of the present study is the establishment of a computational mechanics methodology for developing plasticity-induced cumulative damage models for multilayered structures.

Three-point bending performances of integral-forming aluminum foam sandwich

In the course of service, integral-forming aluminum foam sandwich (IFAFS) needed to bear three-point bending loads in different directions, however, its deformation mechanism and failure modes were still unclear. In this work, three-point bending performances of IFAFS under flatwise and edgewise bending conditions were investigated by experiment, in-situ micro X-ray tomography and digital volume correlation (DVC) calculation. The results showed that three-point bending performance was more stable under edgewise bending condition, and with the decrease of span length IFAFS presented three different failure modes of oblique core shear, asymmetric and symmetrical surface fracture. In addition, porosity mutation was a significant reason for crack initiation, and optimizing pore homogeneity was important to improve the performance and predictability of failure location. Different strengthening effect of sandwich structure anisotropy and different internal deformation evolutions caused by internal strain vortex were two main reasons which lead to performance difference of IFAFS with different solid panel directions. Connection of pre-existing micropores with dimple-like micropores generated during deformation process leads to the failure of IFAFS. The key factors to further optimize three-point bending performance and predictability of IFAFS was to homogenize the pore distribution of IFAFS.

The effect of different air blasting pressure of polyetheretherketone (PEEK) on surface roughness and bond strength to adhesive resin cement: An in-vitro study

Statement of the Problem: Polyetheretherketone material shows good physical and mechanical properties but research is lacking optimum air blasting parameters for good bond strength to resin cement. Aim: To evaluate the effect of different air blasting pressure of PEEK on surface roughness and shear bond strength to adhesive resin cement. Materials and Methods: 24 discs of BioHPP PEEK (bredent, UK) were manufactured. Samples were air blasted with 110 μm Al2O3 particles for 10 seconds at distance of 10 mm and divided into 3 groups according to pressure. Group A: 3 bar, Group B: 2.5 bar and Group C: 3.5 bar. Surface roughness was measured by SEM, Visio Link primer (Bredent, Germany) was applied and cured then G-CEM resin cement (GC, Japan) was applied and cured. Shear bond strength was measured using universal testing machine. EDX analysis was done, and failure mode was detected by stereo-microscope. Results: Statistical analysis showed that roughness average (Ra) increased by increasing pressure, Group B was significantly the lowest (p < 0.05), while there was insignificant difference between other groups (P > 0.05). Regarding shear bond strength, Group A recorded (12.6864 ± 2.486 MPa), Group B (11.2842 ± 1.555 MPa) and Group C (10.1024 ± 2.317 MPa), there was significantly statistical difference between Groups A & C (p < 0.05). The failure mode was mainly adhesive in group C and mixed in groups A & B. EDX analysis showed an increase in Carbon and Silica and a decrease in Oxygen and Aluminum weight percentages after the bond strength test. Conclusion: Increasing the air blasting pressure up to 3 bar increases the surface roughness and bond strength to resin cement, but more than 3 bar showed unfavorable surface roughness and decreased bond strength.

Experimental Study of the Shear Characteristics of Fault Filled with Different Types of Gouge in Underground Gas Storage

In the current international situation, energy storage is an important means for countries to stabilize their energy supply, of which underground storage of natural gas is an important part. Depleted gas reservoir type underground gas storage (UGS) has become the key type of gas storage to be built by virtue of safety and environmental protection and low cost. The multi-cycle high injection and production rate of natural gas in the depleted gas reservoir type UGS will cause the in-situ stress disturbance. The slip risk of fault in the geological system increases greatly compared with that before the construction of the storage engineering, which becomes a great threat to the sealing of the gas storage. Reasonable injection and production strategy depend on the reliable assessment of the shear behavior of the fault belt, which can guarantee the sealing characteristics of the UGS geological system and the efficient operation of the UGS. Therefore, the shear behavior of the fault is studied by carrying out experiments, which can provide important parameters for the evaluation of fault stability. However, there is a large gap between the rock samples used in the previous experimental study and the natural faults, and it is difficult to reflect the shear failure characteristics of natural faults. In this paper, similar fault models based on high-precision three-dimensional scanners and engraving machines, filled with three types of fault gouge, are prepared for a batch of representative direct shear tests. The results show that the peak shear strength of the fault rocks with a shear surface is higher than that of the fault rocks with a tensile surface. Compared with the clay mineral content, the roughness of the fault surface is much more significant for the shear strength of the fault rock. For the fault rocks with similar fault surface morphology, the higher the clay content in the fault gouge, the greater the shear strength of the fault rocks. For the fault rocks with different fault surface morphology and the same fault gouge, the cohesion and internal friction angle of the tensile type is generally smaller than that of the shear type.

Modelling of coupled magnetoelastic waves in structure containing thin antiferromagnetic films on an elastic substrate

In this work we present a model explaining the properties of magnetoelastic waves propagation in the heterostructure containing an antiferromagnetic layer on a non-magnetic elastic substate. Horizontally polarized shear surface waves (SH-waves) propagating in thin film are Love waves. The dispersion characteristic of magnetoelastic waves in such structure was obtained, and the effect of variation of the thickness of the antiferromagnetic layer and the external magnetic field on the frequency of the magnetoelastic resonance was also studied. It was found that an increase in the magnetic field magnitude leads to the increase in the magnetoelastic resonance frequency, and, on the contrary, with an increase in the thickness of the AFM layer the magnitude of the magnetoelastic resonance frequency decreases. The obtained results can be used to develop devices for generating and processing signals in the GHz and THz frequency ranges.

Evaluating die wear-induced edge quality degradation in trimmed DP980 steel sheets from in situ force response monitoring

Assessing trimmed part quality involves periodic examinations of cut edges and shear affected zones to characterize rollover, burnish, fracture and burr formation. Established techniques are thorough and reliable but inherently time consuming. This study correlated die wear-induced force response evolutions and the observed transitions between shear-induced deformation zones for DP980 (C-0.15 wt%Mn-1.5 wt%Si-0.31 wt%) steel sheets subjected to trimming with AISI D2 steel dies. The findings are useful for peripheral assessment of part quality and tool wear via in situ trimming force/displacement response monitoring. Measurements were collected from a load cell and a non-contact laser displacement transducer embedded within the instrumented trimming press. The sliding wear damage and failure processes induced by die–workpiece interactions were correlated to force/displacement response phases. Trimming tests were conducted for 20,000 cycles to observe and assess transformations between rollover and burnish zones with increasing tool wear after the initial contact and at every subsequent 5000 cycle interval. The mean trimming force and maximum die penetration increased, primarily due to die edge blunting, by 1.33 kN (44.3%) and 194 μm (32.2%), respectively. An enlarged die–workpiece contact area increased the resistance force and delayed the onset of fracture with increased sliding damage between sheared surfaces and nearly doubled burnish zone depths. Quantitative attributes of the trimming force/displacement responses were linked to die impact and sliding contact induced damage features of trimmed parts, demonstrating the potential for straightforward, rapid and detailed in-field monitoring of acceptable limits to sheared edge quality.

Role of Surface-Active Element Sulfur on Thermal Behavior, Driving Forces, Fluid Flow and Solute Dilution in Laser Linear Welding of Dissimilar Metals

Understanding heat and mass transfer and fluid flow in the molten pool is very helpful in the selection and optimization of processing parameters, and the surface-active element has an important effect on the heat and mass transfer in laser welding of dissimilar metals. A three-dimensional (3D) numerical model coupled with a sub-model of surface tension, which considers the influence of local temperature and the concentration of surface-active element sulfur at the gas/liquid surface, is used to analyze the thermal behavior, driving forces, fluid flow, and solute dilution during laser linear welding of 304SS and Ni. The relationship between surface tension, driving forces, and the temperature coefficient of surface tension with the spatial distribution of temperature and the surface-active element sulfur is quantitatively analyzed. The simulation results show that the molten pool is fully developed at 45 ms, and the collision of inward and outward convection, with the maximum velocity reaching 1.7 m/s, occurs at the isotherm with a temperature between 2200 K and 2500 K. The temperature-gradient term and concentration-gradient term of surface shear stress play different roles in different positions of the free surface. The local sulfur concentration changes the temperature sensitivity of the surface tension at different sides of the free surface and further determines the transition of convection. Complex fluid flow promotes solute dilution, and the distribution of solute becomes uniform from the front to the rear of the molten pool. The Ni element is transferred to 304SS mainly at the rear side. The work provides theoretical support for the control of joint quality by changing the content of surface-active elements in dissimilar welding.

Warping caused by surface elasticity in a nanowire under torsion

By combining molecular statics simulations and continuum mechanics-based modeling, we show in this paper that the torsion of a $\ensuremath{\langle}001\ensuremath{\rangle}$ single-crystal copper nanowire with a circular cross section gives rise to a warp, i.e., to a displacement field along the wire axis that renders the cross section nonplanar. This behavior, which is in apparent contradiction with what is predicted by continuum mechanics for an isotropic cylinder, can be well explained if we take into account the elastic response of the wire lateral surface. The latter is characterized by the anisotropy of the surface elastic constants and, more specifically in the case of torsion, by the surface shear constant ${C}_{44}^{S}$ whose strength as a function of the local orientation of the lateral surface is estimated independently from atomistic calculations on slabs presenting different vicinal surfaces. The solution of the torsion problem is then obtained by adopting a semi-inverse method in the framework of the finite strain theory in linear elasticity with Gurtin-Murdoch boundary conditions linking surface stress and bulk stress. It is shown that such an approach is well suited to explain quantitatively the warp obtained in our atomistic simulations and to prove the preponderant role played by the surface elastic constant ${C}_{44}^{S}$.

About Shear Properties of Plain Weave Fabric CFRP at High Temperatures: Analytical and Experimental Approaches

The in-plane and interlaminar characteristics of plain weave fabric Carbon Fibre Reinforced Polymer (CFRP) composites are studied. The influence of the temperature exposure, below the glass transition state of the composites, on these properties are studied. The in-plane shear properties, shear strength and shear modulus are affected by the temperature exposure. The in-plane shear strength has dropped by 44.36% for the specimens tested at 120 °C compared to the specimens tested at room temperature. The interlaminar shear strength, however, are largely unaffected by the temperature exposure. The interlaminar shear strength of the plain weave fabric CFRP largely depends on the cross-sectional area of the specimen than the temperature exposure. Finally, several prediction models are used for estimating the shear properties of the composites exposed to different temperatures. Among them, Hawileh model fits very well with the experimental data for predicting the in-plane shear strength, while Wang model fits well for the shear modulus. In addition to these, fracture surfaces of the in-plane shear and interlaminar shear specimens are characterized under optical microscopy to understand the failure modes and how they are influenced by the temperature exposures.

Influence of lithium disilicate pretreatment using photodynamic therapy, non-thermal plasma, and laser treatment on surface roughness and bond strength

AimsTo assess the shear bond strength (SBS) and surface roughness (Ra) of lithium disilicate ceramic (LDC) after using different pretreatment methods i.e., Non-Thermal Plasma (NTP), self-etching ceramic primer (SECP), curcumin photosensitizer (CP), Er and Cr: YSGG lasers (ECL) in comparison to hydrofluoric acid + Silane (HF + S). Materials and methodsA total of fifty LDC discs were prepared. All the discs were arbitrarily divided into five groups based on the surface conditioning used (n = 10). Group 1: PDT+S, group 2: HF+ S, group 3: NTP + S, group 4: SECP, and group 5: ECL+ S. A confocal optical microscope was used to calculate Ra for each sample. A self-adhesive resin cement was applied followed by LED light curing. A universal testing machine was used to assess SBS and a stereomicroscope was used to determine the failure mode. Two-way analysis of variance (ANOVA), and a Tukey post hoc test was used to analyze data (p = 0.05). ResultsThe highest bond integrity of resin luting bonded to conditioned LDS ceramics were presented by group 2 (HF+ S) (21.48±1.39 MPa) and lowest by group 1 (CP+S) (13.01±1.19 MPa) respectively. Intergroup comparison analysis revealed that group 1(13.01±1.19 MPa) and group 3 (14.28±0.62 MPa) displayed comparable outcomes of bond integrity(p>0.05). Similarly, it was observed that group 2 (21.48±1.39 MPa) and group 5 (21.31±1.85 MPa) exhibited comparable values of bond strength(p>0.05). Specimens conditioned with HF+ S showed the highest Ra (1445.86±0.019 µm). However, discs treated with SECP exhibited the lowest Ra (0139.76±0.081 µm). ConclusionEr, Cr: YSGG laser retains the ability to be used as an LDC surface conditioner as an alternative to HF+ S.Both the methods of pretreatment results in high surface roughness of LDC.

Testing the Shear Strength of Mass Concrete Lift Lines: A Comparison of Procedures

Accurately evaluating the break bond and sliding shear strength of mass concrete lift lines is critical for any structural analysis of a dam. Of paramount importance and difficulty is the determination of break bond strength and of realistic peak and residual sliding shear strength parameters, in order to develop the anticipated strength degradation with shear displacement. Traditional multistage direct shear testing repeatedly shears the same specimen surface under increasing normal loads. The first sliding stage post-break bond has the freshest shear surface, which then degrades with each subsequent sliding stage, resulting in an artificially lower sliding friction angle and higher apparent cohesion due to accumulated damage on the shear surface. A novel approach has been proposed that, when a group of specimens are assumed to have similar characteristics, utilizes a matrix-based variable normal loading schedule that develops unique insight into shear strength degradation with sliding displacement. To eliminate the uncertainty as to which approach should be used and when, this paper documents a unique laboratory testing program where two different direct shear procedures were used for two differently sized cores obtained from the Thief Valley Dam. The two procedures were: (1) a state-of-the-art matrix-oriented approach which varies the order of the normal loads applied to develop an understanding of the shear strength degradation with sliding displacement, and (2) the typical direct shear procedure outlined in ASTM D5607, where normal loads are applied in an increasing order. This paper presents the results from: (1) the two different direct shear testing procedures and (2) the obtained strength parameters of the different core sizes.

Thermocapillary migration of a deformed droplet in the combined vertical temperature gradient and thermal radiation

Thermocapillary migration of a deformed droplet in the combined vertical temperature gradient and thermal radiations with uniform and non-uniform fluxes is first analyzed. The creeping flow solutions show that the deformed droplet has a slender or a cardioid shape, which depends on the form of the radiation flux. The deviation from a sphere depends not only on the viscosity and the conductivity ratios of two-phase fluids but also on capillary and thermal radiation numbers. Moreover, in the roles of interfacial rheology on thermocapillary migration of a deformed droplet, only the surface dilatational viscosity and the surface internal energy can reduce the steady migration velocity, but the surface shear viscosity has not any effects on the steady migration velocity. The surface shear and dilatational viscosities affect the deformation of the droplet by increasing the viscosity ratio of two-phase fluids. The surface internal energy directly reduces the deformation of the droplet. However, the deformed droplet still keeps its original shape without the influence of interfacial rheology. Furthermore, it is found that, based on the net force balance condition of the droplet, the normal stress balance at the interface can be used to determine the steady migration velocity, which is not affected by the surface deformation in the creeping flow. From the expressions of the normal/the tangential stress balance, it can be proved that the surface shear viscosity does not affect the steady migration velocity. The results could not only provide a valuable understanding of thermocapillary migration of a deformed droplet with/without the interfacial rheology in a vertical temperature gradient controlled by thermal radiation but also inspire its potential practical applications in microgravity and microfluidic fields.

Impact of Hall Current and Joule Heating on a Rotating Hybrid Nanofluid Over a Stretched Plate with Nonlinear Thermal Radiation

The impact of magnetic field, joule heating, rotation parameter, Hall current, with nonlinear thermal radiation, on a rotating hybrid Fe3O4/Al2O3 nanofluid over-stretched plate is the focus of this research. Using similarity transformations, the controlling partial differential equations are turned into a set of nonlinear ordinary differential equations. For that system of equations, the shooting method is used to generate numerical solutions. The impact of various entry parameters on transversal and longitudinal velocities, temperature, heat flow and surface shear stress are studied numerically and graphically. The results obtained confirm that When hybrid nanoparticles are present, skin friction on the surface increases by (31.91%–51.27%) and the Nusselt number falls by (4.4%–7.57%) for 5% Al2O3 plus (5%–10%) magnetite.

Structure Identification of Adsorbed Anionic–Nonionic Binary Surfactant Layers Based on Interfacial Shear Rheology Studies and Surface Tension Isotherms

Mixtures of anionic sodium oleate (NaOl) and nonionic ethoxylated or alkoxylated surfactants improve the selective separation of magnesite particles from mineral ores during the process of flotation. Apart from triggering the hydrophobicity of magnesite particles, these surfactant molecules adsorb to the air-liquid interface of flotation bubbles, changing the interfacial properties and thus affecting the flotation efficiency. The structure of adsorbed surfactants layers at the air-liquid interface depends on the adsorption kinetics of each surfactant and the reformation of intermolecular forces upon mixing. Up to now, researchers use surface tension measurements to understand the nature of intermolecular interactions in such binary surfactant mixtures. Aiming to adapt better to the dynamic character of flotation, the present work explores the interfacial rheology of NaOl mixtures with different nonionic surfactants to study the interfacial arrangement and viscoelastic properties of adsorbed surfactants under the application of shear forces. Interfacial shear viscosity results reveal the tendency on nonionic molecules to displace NaOl molecules from the interface. The critical nonionic surfactant concentration needed to complete NaOl displacement at the interface depends on the length of its hydrophilic part and on the geometry of its hydrophobic chain. The above indications are supported by surface tension isotherms.

Condensation heat transfer of binary and ternary mixtures inside multiport tubes

This study investigated the condensation heat transfer of pure refrigerants and binary and ternary mixtures inside horizontal multiport tubes with multiple square minichannels. The effects of mass flux, vapor quality, heat flux, channel size, and channel shape were evaluated using pure refrigerants R32 and R1234yf; binary mixtures R32/R1234yf, R32/R1123, R32/R13I1, and R410A; and ternary mixtures R1123/R32/R1234yf and CO2/R32/R1234yf. For pure refrigerants, the heat transfer coefficient in the annular and churn flow regimes decreased monotonically with decreasing vapor quality. By contrast, the heat transfer coefficient in the plug flow regime was higher over a wide vapor quality range because of the thin condensate film formed by surface tension. Smaller channels exhibited higher heat transfer coefficients. The square minichannels exhibited higher heat transfer coefficients than the circular minichannels, except in the region with high mass flux and high vapor quality. For binary and ternary mixtures, the heat transfer coefficients significantly decreased with decreasing mass flux and vapor quality and were strongly deteriorated at lower mass fluxes. Compared with the annular and churn flow regimes, in the plug and slug-annular flow regimes, where heat transfer through the thin liquid film was dominant, the effect of mass diffusion resistance in deteriorating heat transfer was the most pronounced. A new heat transfer model for pure refrigerants inside multiport tubes with multiple rectangular minichannels was developed considering the contributions of vapor shear stress and surface tension. The proposed model was verified using a dataset of pure refrigerants, and a mean absolute percentage error (MAPE) of 11.5% was achieved. Furthermore, a new heat transfer model that considers the heat transfer deterioration of non-azeotropic refrigerant mixtures was proposed, which could predict 508 datapoints with an MAPE of 13.3%.

Fracture mechanism and model of AA7075 multi-cavity component formed under complex stress states

During the multi-directional loading forming process of AA7075 aluminum alloy multi-cavity component, the stress states of material are complex and cracking defects are easy to occur, which seriously restricts the smooth process implementation and the improvement of forming quality. In this paper, based on the characteristic structure of AA7075 multi-cavity component, the material flow and stress states were studied. A trapezoidal groove shape specimen and test device were ingeniously designed. Then the fracture morphology, microstructure and mechanism of AA7075 alloy under different stress states are revealed. The results show that when the stress state changes from tensile-shear to pure shear and compression-shear, the fracture is easy to occur at the second phase particles, inclusions, the interface of elongated and equiaxed grains. The fracture modes are the mixture of surface shear fracture and core tensile fracture, but the proportion of shear plane is increasing. The grain morphology at the fracture surface is long grain with slightly increased axial diameter ratio, equiaxial grain with sufficient dynamic recrystallization, and slender shear band with large angle deflection, respectively. Further, a thermoforming fracture model under complex stress states in the process of multi-directional loading forming of multi-cavity components is established.