This research involves stress-strain analysis in poly(methyl methacrylate) (PMMA) octagonal shape compressed by hydraulic system. The observation of uniaxially stressed samples was carried out using ...reflection photoelasticity technique. The results of fringe order number and principal stress angle were used to determine stress and strain distribution in the samples by shear difference method. It was found that high stress-strain region was close to the contact point where compressive force was applied but it was zero at the edge of the samples. The area of high strain region increased as the magnitude of force was increased but it decreased as the dimension of octagonal shape was increased.
Additive manufacturing is revolutionizing processing in many applications including 3-D food printing. So far the number of suitable printable materials for food is limited and the microstructure and ...texture properties of 3-D printed food have been characterized poorly. This study introduces the novel concept of customizable water-based porous food simulants by 3-D printing using low methoxylated pectin gel as food-ink. A series of pectin gels was successfully 3-D printed by changing the formulation parameters including stirring rate and pectin, CaCl2, bovine serum albumin and sugar syrup concentrations. It was shown that food objects with variable microstructure and texture properties can be 3-D printed by using different pectin based food-inks. The pectin concentration was the main determinant of firmness and strength of the printed object. Sugar and pectin concentrations increased viscosity and affected the build quality. BSA stabilized and promoted the aeration of the food-ink. This resulted in a pore size distribution after printing that was influenced by the viscosity of the food-ink. A predictive model was established for designing the food-ink composition to obtain 3-D printed food simulants with a priori defined microstructure and texture.
•Edible objects were successfully 3-D printed using low methoxylated pectin gels.•Objects with variable properties were printed by changing the food-ink composition.•Bovine serum albumin stabilized the air bubbles in the food-ink.•Sugar syrup increased the viscosity of the food-ink and may result in better build quality•The CaCl2 concentration had to be adjusted with respect to the pectin concentration.•The models may be used as a tool to formulate customized pectin-based food.
Most of the notched components for ground vehicles experience complex multiaxial loadings, where principal stresses rotate and change non-proportionally their magnitudes during a loading cycle. ...Furthermore, many vehicle components contain notches and geometrical irregularities because of design requirements. These geometric discontinuities cause significant stress concentrations. Multiaxial loads result in complex stress and strain responses at notch areas and can induce a fatigue failure even without any warning of noticeable plastic deformation. Unfortunately, the combination of multiaxial loading paths and complex geometries of mechanical components is unavoidable in practice and experiments performing durability test for ground vehicles are often not feasible because of time and cost considerations.
Therefore, an innovative computational fatigue analysis methodology has been proposed here for multiaxial fatigue life analysis of notched components under design process using analytical and numerical methods. The proposed multiaxial fatigue analysis methodology consists of an elastic–plastic stress–strain model and a multiaxial fatigue damage parameter. Computed results of the proposed methodology are compared to sets of experimental published data to verify the prediction capability of the elastic–plastic stress–strain model and the fatigue damage parameter. A comparison of analysis results and experimental data shows that the multiaxial elastic–plastic stress–strain model correlates well with experimental strain data for SAE 1070 steel notched bars subjected to complex non-proportional load paths. The proposed fatigue damage parameter correlates well with fatigue data of 1045 steel and Inconel 718 tubular specimens under proportional and non-proportional loadings. Finally the complete analysis methodology incorporating both the elastic–plastic stress–strain model and the multiaxial fatigue damage parameter is found to be in a good agreement with experimental data of SAE 1045 steel notched shafts subjected to proportional and non-proportional loadings.
Hundred-megahertz bands are widely used in long/short-range communications, such as satellite service and walkie-talkies. Due to the wavelength exceeding 1 meter, most hundred-megahertz mobile ...antennas are long-external whips, which not only affect portability but also degrade mechanical strength. This work proposes the first foldable hundred-megahertz mobile antennas. Mobile terminals are mostly in standby mode, so eliminating external antennas in standby mode is beneficial for portability and strength. A segment of nitinol memory alloy is adhered to a flexible copper-clad laminate, constituting the foldable antenna branch. In standby mode, the antenna is completely hidden on side surface of the terminal under external force. In operational mode, release of the force allows the antenna to spring out quickly and exhibit high performance. The mechanical property of the nitinol alloy is analyzed. The proposed antenna operates at two frequencies, with the printed copper strip for 280 MHz and nitinol for 433.92 MHz. Classical doughnut-shaped patterns with the measured maximum gains of 1.1/1.8 dBi and out-of-roundnesses of 1.9/1.3 dB are obtained. The reflection coefficient is stable after folding 50~500 times, demonstrating robust mechanical performance and practical value. The proposed strategy offers a higher level of portability and operational convenience compared with traditional retractable solutions.
This study aimed to analyze experimentally and by modeling the shrinkage deformation of Japanese eggplant (Solanum melongena) during roasting by simultaneous heat and moisture transport model coupled ...with a structural mechanics model applicable to a body undergoing volumetric changes, as a consequence of moisture removal. Cylindrical slices (45 mm × 10 mm) were roasted for up to 15 min. Roasting experiments were performed using a convection-oven at 250 °C. Several coefficients and parameters required for calculations were experimentally obtained. An implicit finite element method was applied using a FORTRAN program. In this study, an approximately equal reduction rate in moisture content losses and volume shrinkage was observed (R2 ≥ 0.99). The volumetric (Sv) and directional shrinkage were successfully estimated by developed empirical equations (e.g. R2 > 0.98 for Sv). The simulation of temperature and moisture distribution undergoing shrinkage deformation confirmed the importance of internal evaporation in the transport model.
•A theoretical description of shrinkage in a visco-elastic material was provided.•Shrinkage velocity is equal to water lost during roasting of eggplant.•Directional analysis shows more shrinkage in thickness than in the radial direction.•Estimation of internal evaporation improves the simulated results.•Interactions between transport phenomena and shrinkage were successfully modeled.
Through characterizing the interaction of normal/shear stress–strain behavior on material planes of TC4 alloys, a new strain energy critical plane model describing mean stress effects is proposed for ...life prediction under tension–compression, pure torsion, and tension–torsion loadings. Moreover, a modified Ince–Glinka model is elaborated through considering crack surface close to the maximum shear strain plane. Three simple solutions are presented to determine cracking failure mode using the concepts of life, damage, and strain. Comparing with lifing models of Liu, Smith–Watson–Topper, and modified Ince–Glinka, the proposed model provides more accurate life predictions for TC4 and a compressor turbine disc by full-scale fatigue testing.
A coaxial extrusion printhead was designed for 3D printing of pectin-based food simulants in which the inner flow is the food-ink and the outer a CaCl2 crosslinking solution. A series of cubic-shaped ...objects was successfully 3D printed by changing the printing parameters including the food-ink composition, the layer height, and the rate and CaCl2 concentration of the outer flow. The printed objects did not necessitate any incubation post-treatment because the gelation of the food-ink occurred during the printing. The mechanical properties of the printed object were correlated to their final Ca2+ concentration which can be controlled by the rate and CaCl2 concentration of the outer flow. A predictive model was established for determining the printing settings to print 3D objects with a priori defined texture. The layer height was recommended to be set in function of the food-ink swelling behavior. Finally, we compared objects printed by coaxial and simple extrusion methods. The compared objects had similar Young's moduli but their other properties including volume and final Ca2+ concentration, were considerably impacted by the printing method.
•Coaxial printing allows simultaneous deposition of pectin-based food-ink and CaCl2 solution.•The coaxial printing avoids the requirement of incubation post-treatment.•Mechanical properties of printed objects can be controlled with the outer flow settings.•Setting appropriate printing parameters is important to have good printing quality.•Coaxial and simple extrusion printing affect the properties of printed objects.
Abstract
High temperature REBCO superconducting tapes are very promising for high-field magnets. With high magnetic field application there are high electro-mechanical forces, and thus concern for ...mechanical damage. Due to the presence of large screening currents and composite structure of the tape, the mechanical design of these magnets are not straight forward. In addition, many contemporary designs use insulated winding. In this work we develop a novel two-dimensional axisymmetric finite element tool programmed in MATLAB that assumes the displacement field within linear elastic range. The stack of pancakes and a large number of REBCO tape turns are approximated as an an-isotropic bulk hollow cylinder. Our results agree with uni-axial stress experiments in literature, validating the bulk approximation. Here, we study the following configuration. The current is first ramp up to below the critical current and we calculate the screening currents and the forces that they cause using the MEMEP model. This electromagnetic model can now take insulated magnets into account. As a case study 32 T REBCO superconductor magnet is simulated numerically. We have done complete mechanical analysis of the magnet by including the axial and shear mechanical quantities for each pancake unlike previous work where only radial and circumferential quantities are focused. Effect on mechanical quantities without screening current is also calculated and compared. It is shown that including screening current induced field strongly affect the mechanical quantities, specially the shear stress. The latter might be the critical quantity for certain magnet configurations. Additionally, in order to overcome high stresses, a stiff over banding of different material is considered and numerically modelled which significantly reduces the mechanical stresses. The FE based model developed is efficient to calculate the mechanical behaviour of any general superconductor magnet and its devices.
This study investigated the effects of Pb2O3 nanoparticles on the thermal, mechanical, and shielding properties of epoxy resin, liquid silicone rubber, and polyvinyl chloride composites which have ...been proposed as efficient substitutes for traditional lead-based materials for shielding gamma and X-ray radiations. The Pb2O3 nanoparticles were synthesized using a low-cost electrochemical method, characterized by XRD and SEM analysis, and uniformly dispersed in the polymer matrix by casting technique. The mechanical and thermal properties of the samples were investigated by stress-strain and TGA analysis, and the effectiveness of Pb2O3 in improving the radiation shielding capabilities of the polymers was investigated by analyzing parameters such as the mass attenuation coefficients and the half-value layer factor for gamma rays. The results showed that the addition of Pb2O3 nanoparticles had no adverse effect on the thermal stability of polyvinyl chloride (PVC) composites; at the same time, it decreased the thermal stability and increased the weight loss of Epoxy Resin (ER) and Liquid Silicon Rubber (LSR) composites. The nanocomposites had higher tensile strength and modulus of elasticity than the original polymer, and their shielding properties improved with increasing nanofiller content. This study provides insights into modifying the properties of composites using fillers and polymers to improve their properties for various applications.
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•Different epoxy resin, silicone, and PVC-based Pb2O3 nano composites (namely 10, 20, 30, and 40 wt%) were produced.•Low-priced electrochemical synthesis method was used to synthesize Pb2O3 nano particles.•Thermal, mechanical, and shielding properties of constructed nano composites were experimentally assessed.•Findings: PVC thermal stability unaffected by Pb2O3 nanoparticles. ER and LSR composites' stability reduced; weight loss increased.•Nanocomposites surpassed original polymer in strength, elasticity, and shielding with increased nanofiller content.
