Static Tensile Mechanical Properties Research Articles

Conformation Effect on the Mechanical and Microbiological Behavior of Invisible Orthodontic Aligners.

Invisible orthodontic aligners are having a great impact on tooth movement in an aesthetic and effective way. Different techniques, models, and clinical aspects have been studied for their proper use. However, the aim of this research has been to determine the effect of the shaping process on mechanical properties and their bacterial behavior. For this study, 40 original polyurethane plates and 40 identical models, obtained by hot forming the original plates, were used. The static tensile mechanical properties were studied with a Zwick testing machine using testing speeds of 5 mm/min at a temperature of 37 °C. The original plate and the aligner have been studied with a creep test by subjecting the samples to a constant tension of 30 N, and determining the elongation using a long-distance, high-resolution microscope at different time periods between 1 and 720 h. Studies of water absorption has been realized with artificial saliva for 5 h. Bacterial cultures of Streptococcus oralis and Actinomyces viscosus strains were grown on the original plates and on new and used models, to determine the proliferation of each bacterium through metabolic activity, colony-forming units, and LIVE/DEAD assays. The mechanical results showed an increase in the strength of the inserts with respect to the models obtained from 3.44 to 3.95 MPa in the elastic limit and a lower deformation capacity. It has been proven that the transition zone in the creep curves lasts longer in the original plate, producing the rapid increase in deformation at a shorter time (400 h) in the aligner. Therefore, the shaping process reduces the time of dental correction exerted by the aligner. The results of the bacterial culture assays show an increase in the number of bacterial colonies when the aligners have been used and when the polyurethane is conformed due to the internal energy of the model, with respect to the original polyurethane. It has been observed that between the original plate and the aligner there are no statistically significant differences in water absorption and therefore the forming process does not affect water absorption. A slight increase in water absorption can be observed, but after five hours of exposure, the increase is very small.

Static tensile mechanical properties and engineering application of constant resistance and large deformation anchor cable

Deep engineering is faced with mechanical phenomena, such as substantial soft rock deformation and in situ stresses, that results in frequent disasters because the energy of the surrounding rock cannot be released normally after excavation. Traditional support materials have low elongation and safety reserves, cannot adapt to large deformations of the surrounding rock, and cannot apply high preload, making it difficult to absorb energy. This study introduces a new type of constant resistance and large deformation (CRLD) cable through static tensile experiments, and compared the results of which with those of ordinary high-strength (HS) cables. Our results showed that the CRLD cable had an obvious constant resistance stage, with a constant resistance value of approximately 415 kN and an elongation rate as high as 25%, which is 3.9 times that of the HS cable. Furthermore, the energy absorption of the CRLD cable was 3.5 times that of the HS cable. Before the first steel strand broke, the temperature of the entire cable was approximately 33 °C, and the energy was absorbed evenly without obvious energy concentration. After breaking, the standard deviation of the segmental elongation of the steel strand was 4.16 mm, with a small degree of dispersion. The deformation of each section of the steel strand was uniform lengthwise and the necking rate of the fracture was 8.5%, indicating that there was no obvious necking. On this basis, a comprehensive mechanical performance evaluation index of the cable, that is, the static toughness UT, was proposed, reflecting the strength, elongation, and energy absorption density of the cable. Compared with the HS cable and another widely used He cable with excellent energy absorption characteristics, the UT of the CRLD cable was 117% higher than that of the HS cable and 38.1% higher than that of the He cable. This study also proposes a support and design principle for the CRLD cable and applies a CRLD cable to a roadway with a buried depth of 1050 m. Our results show that, owing to the high-strength reserve of the CRLD cable, the applicable preload can reach more than 85% of the breaking load of the cable, which is 2.3 times that of the HS cable. After this new support was adopted, the maximum deformation of the surrounding rock of the roadway was 180 mm, which is 36% of that of the traditional support. The deformation of the roadway was controlled and the surrounding rock was stable.

Lateral impact performance of wire ropes

Wire ropes are often used in flexible barriers or road engineering to resist lateral impact because of their good reliability, high economy, and construction convenience. However, their application under lateral impact lacks a systematic design approach. In this paper, to ensure the safe use of the structure, the lateral impact test of single wire ropes and wire rope nets is carried out, and the strain, displacement, and acceleration response are analyzed. In addition, the tensile mechanical properties of wire rope strands are determined through static tensile mechanical properties tests, which provide reasonable parameters for the constitutive model used in numerical simulations. Furthermore, considering the influence of wire rope pre-tension ratio, span ratio, and mass ratio, empirical formulas for longitudinal peak tensile force and lateral peak displacement are given. The results show that the wire rope mainly occurs local abrasion at the impact point, fracture, and end connection failure. It is worth noting that when the dimensionless lateral peak displacement (ωm) reaches 0.089, the wire rope breaks. Moreover, according to Lagrange Green’s strain theory, a theoretical calculation formula for the mid-span lateral limit displacement of wire rope under pre-tension is derived and compared with the simulated values of test members. Consequently, according to the damage degree of wire ropes, the damage limit value is determined. Finally, considering the tensile capacity of wire ropes and their displacement responses, a limit state function is proposed to evaluate the damage of existing components or to design new components.

Study on Properties of Energetic Plasticizer Modified Double‐Base Propellant

AbstractTo improve the low‐temperature mechanical properties of double‐base propellants, the effects of three energetic plasticizers (geminal dinitro aldehyde acetal plasticizer, azido‐terminated glycidyl azide polymer, and ester‐terminated glycidyl azide polymer) on the low‐temperature mechanical properties of nitrocellulose (NC)/nitroglycerin (NG) propellant were studied firstly in this article. It was found that azido‐terminated glycidyl azide polymer (GAPA) was the most effective plasticizer to improve the low‐temperature mechanical properties of NC/NG propellant. Then the effects of GAPA on the low‐temperature static tensile mechanical properties, thermal stability, dynamic thermomechanical properties, density, and heat of detonation of fully‐formulated double‐base propellant with ETPE were studied. It was found that the double‐base propellant with 1 % GAPA had the best comprehensive performance, and its maximum tensile strength and elongation at break at low temperature (−40 °C) were 56.16 MPa and 10.63 %, respectively. The elongation at break was increased by 10.2 % compared to the double‐base propellant without an energetic plasticizer. Meanwhile, the correlation between dynamic and static mechanical properties of the double‐base propellant with 1 % GAPA was also studied, and the relationship between the dynamic storage modulus and the static tensile strength was obtained.

Hygrothermal effects on fatigue behavior of quasi-isotropic flax/epoxy composites using principal component analysis

This work studies the long-term hygrothermal (HT) aging effect on the fatigue behavior of a flax/epoxy bio-composite arranged in [02/902/±45]S lay-ups. The effect of aging on static tensile mechanical properties was first investigated. Tension–tension fatigue tests were also performed for both unaged and aged samples. The distribution of fatigue life for both unaged and aged sample was determined. The evolution of fatigue properties was also investigated. Fatigue tests were coupled with acoustic emission (AE) for a better understanding of how these composites react to fatigue loading in wet environmental conditions. Static tests show that water absorption affects negatively the elastic properties of this material. S–N curves show a good performance in fatigue strength of unaged samples. This performance dropped significantly with HT aging. The analysis of stress–strain hysteresis loops allowed to determine the minimal strain such as the desirable fatigue properties to explain fatigue damage evolution for single stress component. Hwang–Han’s model based on minimal strain was also used to predict the fatigue damage of the tested flax/epoxy composites. Principal component analysis enabled to separate the fatigue damage evolution of unaged and aged samples. AE results confirmed that the damage evolution of both samples is not the same. AE analyses were permitted to identify the growing fiber/matrix debonding and pull-out mechanism in the unaged samples. Correlation between AE and scanning electron microscope observations enabled the identification of several damage mechanisms and their evolution during the fatigue tests.

Dynamic and static tensile mechanical properties of myocardial tissue.

Event Abstract Back to Event Dynamic and static tensile mechanical properties of myocardial tissue. Sherif Ramadan1, 2, 3, Hani Naguib1, 2, 3 and Narinder Paul3, 4 1 University of Toronto, Mechanical and Industrial Engineering, Canada 2 University of Toronto, Smart and Adaptive Polymers Lab, Canada 3 University of Toronto, Institute of Biomaterials and Biomedical Engineering, Canada 4 Toronto General Hospital, Joint Department of Medical Imaging, Canada Introduction: Heart disease is a significant cause of morbidity and mortality that affects 1.3 million Canadians annually[1]. Coronary artery disease (CAD) is a leading cause of heart disease and is due to progressive accumulation of arterial plaque resulting in occlusion of the arterial lumen and abnormal myocardial contractility[2]. Computed Tomography Coronary Angiography (CTCA) is used to exclude significant CAD in patients with low-intermediate pre-test probability[3],[4]. However, dynamic anthropomorphic CT phantom devices that realistically mimic normal and diseased cardiac tissues are required to test new imaging techniques and algorithms that target ultralow radiation dose and high resolution CTCA. This study aims to quantify the mechanical properties of myocardial tissue to allow for the fabrication of phantoms that mimic the behaviour of heart tissue under varying hemodynamic conditions. Materials and Methods: The elasticity of myocardial tissue was tested under static and dynamic conditions. Tensile testing was performed to obtain the Young’s modulus and a dynamic mechanical analyzer (DMA) induced a frequency sweep to determine the complex (dynamic) modulus. A frequency range of 0.5Hz to 3.5Hz was analyzed as these frequencies correspond to human heart rates of 30 to 210bpm. Multiple tissue samples were taken from each pig and lamb heart, these animal models were chosen as they are close human analogues and are commonly used as replacements for human tissue[5],[6].The heart tissue was tested while freshly sacrificed without any intervening freeze-thaw cycles to ensure the integrity of the muscle tissue. The tissue was placed in a balanced salt solution and tested at 37°C to simulate in vitro conditions[7]. Results and Discussion: Preliminary data (mean ± SD): The tensile and complex moduli were tested on 6 pig and lamb hearts; tensile modulus of lamb = 0.06 ±0.03 (n=15 samples) and for pig =0.04 ± 0.03 (n=11 samples); the complex modulus for lamb = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± 0.02 (n=15 samples) and for pig = 0.03Mpa at 0.5Hz to 0.06 Mpa at 3.5Hz ± .01 (n=15 samples) and both exhibited a linear trend. These values indicate that myocardial tissue behaves similarly to soft rubbers and stiffens under higher frequency loads. Moreover, for tensile testing there was no statistical difference between individual hearts or animals (P values of 0.235, 0.483, and 0.73 between the animals, pig hearts, and lamb hearts respectively). Conclusions: The static and dynamic moduli of myocardial tissue in pig and lamb hearts is between 0.02 and 0.1Mpa which is similar to soft, rubber-like materials. This quantitative data will inform selection and fabrication of customized biomaterials for construction of the myocardium in a dynamic anthropomorphic tissue realistic heart phantom.

Effect of thermal history on the mechanical properties of three polypropylene impact-copolymers

The effect of thermal history on static mechanical properties and impact fracture behavior of three reactor polypropylene impact-copolymers (ICPPs) was investigated for three ICPPs prepared using commercial Innovene ®, Unipol ® and Spheripol ® polymerization technologies. Multiple extrusion employing a co-rotating twin-screw extruder resulted in a significant reduction of the molecular weight of the PP homopolymer phase evidenced by the increasing melt flow index (MFI). Neither cross-linking of the ethylene-propylene rubber (EPR) phase nor EPR particle coarsening was detected for any of the ICPPs after 5 consecutive extrusions. Decreasing molecular weight of the PP homopolymer phase caused change in the crystalline morphology of injection molded specimens due to the change in crystallization kinetics and reduction of the number of tie molecules, however, the overall degree of crystallinity did not change, significantly. The static tensile mechanical properties (E, σ y, ɛ b), critical strain energy release rate, G c, and the Charpy notched impact strength, a k, decreased with increasing MFI in a monotonous manner for all the ICPPs investigated. Despite significant differences between the absolute values of the mechanical properties for the three ICPPs, the MFI dependence of the σ y and G c relative to that for the unaffected ICPP fell on a single master curve for all of them. High-speed digital camera, used to follow the fracture process during the instrumented impact test, revealed no significant change of the small scale yielding fracture process with increasing MFI. This was in an agreement with the negligible change in the size of the crack tip plastic zone, R p, predicted using simple mixed mode fracture model. The plane strain value of the critical strain energy release rate, G 1c, calculated from the measured G c for the INN (2.4 kJ/m 2), UNI (2.8 kJ/m 2) and SPH (3.5 kJ/m 2) using a simple LEFM model did not exhibit significant dependence on the number of extruder passes. The observed differences between the three ICPPs were ascribed to the significantly larger EPR content in UNI compared to the other two ICPPs and significantly larger content of isotactic PP homopolymer in the INN compared to the remaining two ICPPs.

Synthesis of a random copolymer and its compatibility for thermotropic liquid crystalline polymer/poly(ether ether ketone) blends

AbstractA random copolymer (RCP) containing poly(ether ether ketone) (PEEK) and thermotropic liquid crystalline polymer (TLCP) segments was synthesized. Its chemical structure and liquid crystalline properties were characterized by FT‐IR, differential scanning calorimetry (DSC) and polar light microscopy (PLM) respectively. A single glass transition temperature (Tg) at 134.0°C, a melting temperature (Tm) at 282.0°C and a temperature of ignition (Ti) at 331.3°C can be observed. Blends of PEEK and TLCP with and without RCP as compatibilizer were prepared by extrusion and the effect of RCP on the thermal properties, dynamic mechanical properties, morphology and static tensile mechanical properties of blends was investigated by means of DSC, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), etc. Dynamic mechanical measurements indicated that there appeared to be only a single tan δ peak resulting from the glass transition of the PEEK‐rich phase and the Tg value shifted towards higher temperature due to the presence of compatibilizer, as suggested partial compatibility. Morphological investigations showed that the addition of RCP to binary blends reduced the dispersed phase size and improved the interfacial adhesion between the two phases. The ternary compatibilized blends showed enhanced tensile modulus compared to their binary blends without RCP. The strain at break decreased for the ternary blends due to embrittlement of the matrix by the incorporation of some RCP to the matrix phase. Copyright © 2007 John Wiley & Sons, Ltd.

Tensile Fracture and Failure Behavior of Thermoplastic Starch with Unidirectional and Cross‐Ply Flax Fiber Reinforcements

AbstractThermoplastic starch (MaterBi®) based composites containing flax fibers in unidirectional and crossed‐ply arrangements were produced by hot pressing using the film stacking method. The flax content was varied in three steps, viz. 20, 40 and 60 wt.‐%. Static tensile mechanical properties (stiffness and strength) of the composites were determined on dumbbell specimens. During their loading the acoustic emission (AE) was recorded. Burst type AE signal characteristics (amplitude, width) were traced to the failure mechanisms and supported by fractographic inspection. The mechanical response and failure mode of the composites strongly depended on the flax content and the flax fiber lay‐up. It was established that the tensile strength increases until 40 wt.‐% flax fiber content but stays almost constant above this value. In the case of 40 wt.‐% unidirectional fiber reinforcement, the tensile strength of the composite was 3 times greater than that of the pure starch matrix. The flax fiber reinforcement increased the tensile modulus of the pure starch by several orders of amplitude.SEM picture of the fracture surface of a composite with UD flax reinforcement.magnified imageSEM picture of the fracture surface of a composite with UD flax reinforcement.

Properties of blends of starch, polyethylene and poly(ethylene-co-acrylic acid) copolymer

Using reactive extrusion in a twin-screw extruder the blends of low-density polyethylene (PE-LD) with poly(ethylene-co-acrylic acid) (EAA) copolymer 1:1 and 5-30 weight % of potato starch (oxidized - OP or non-oxidized - P) or corn starch (C) were prepared. The static tensile mechanical properties, hardness and melt flow rate (MFR) of the samples were determined. The course of biodegradation of the samples under the influence of selected, amyloliticly active, bacteria strains, actinomycetes and filamentous fungi. Biodecomposition degree has been estimated on the basis of macroscopic and microscopic observations and FT-IR spectrometry. All the samples supported the growth of microbes, the blends with OP - much higher than those with C. It has been also found that biodecomposition degree increased with the starch content in the blend. The highest degree of biodecomposition was observed when Aspergillus niger, Streptomyces (strain 19) and mixture of bacteria of Bacillus type were used.