Proportional Limit Research Articles

Crack propagation analysis of SiC f/SiC composites by gas permeability measurement

Permeability of helium gas through the NITE-SiC f/SiC composites after applying tensile stress was measured experimentally in a vacuum apparatus. Tensile stress equal to 1.1–1.2 times the proportional limit stress (PLS) was applied parallel to the direction of the reinforced fiber. Results of the permeability experiments revealed that the permeability rapidly increased when threshold stress was applied on the specimens. The permeability of helium gas was governed by the narrowest diameter of the permeation pathway. In the case of NITE composites, the diameter of the pathway was calculated to be below 0.65 μm. The NITE composites exhibited superior performance even when the applied stress was greater than 1.2 times the PLS. Fiber bundles considerably magnified the permeability of helium gas because of the relatively large pore size of the intra-fiber bundles. Transverse cracks propagated with increasing stress and they connected fiber bundles when the applied stress was 1.10–1.15 times the PLS.

Tensile test technique for composites using small notched specimens

Development of small specimen test techniques is one of the key issues for irradiation studies. This study primarily aims to develop a new tensile test method using small notched tensile specimens. For that purpose, the crack extension behavior of the notched tensile specimens was first evaluated. Observing the crack propagation behavior, the apparent notch insensitivity of the axial tensile properties was identified. Due to the notch insensitivity, it was found that the key tensile properties such as the proportional limit stress and ultimate tensile strength can easily be predicted from the test results on the notched specimens. In contrast, for the off-axial tensile tests, the apparent notch sensitivity was identified.

Shear Capacity of Dowelled Mortise and Tenon in Tropical Timber

The European Yield Models (EYM) concept has been applied to observe an experimental study of single-dowelled mortise and tenon. Specimens consisting of structural size mortise and tenon dowelled with 20.6 mm diameter were axially loaded in shear. Test variables are the material for the dowels namely steel; glass fibre reinforced plastic (GFRP) and wood. Connections were tested until failure to observe the ultimate capacities and possible modes of failure as the variables were changed. Results show that the shear strength capacity of the mortise and tenon connection single-dowelled with steel, GFRP and wood is not directly reflected the capacity of the dowel. The proportional limit, 5% diameter offset and maximum strength of the connection are in the order of steel, wood and GFRP but the dowel yield modes are in the order of steel, GFRP and wood. Failure modes of GFRP were found as stiff as steel (mode Im) compared to wood (mode IIIs).

Effect of location of glass fiber-reinforced composite reinforcement on the flexural properties of a maxillary complete denture in vitro

Objective. To evaluate the effect of the location of glass fiber-reinforced composite (FRC) reinforcement on the flexural load at the proportional limit (FL-PL) and the flexural deflection of a maxillary acrylic resin complete denture. Material and methods. Maxillary acrylic resin complete dentures strengthened with and without FRC reinforcement were tested. The polymerized FRC was embedded in the denture base resin in the doughy state and placed (1) under the ridge lap region, (2) in the anterior region, (3) in the middle region or (4) in the anterior and posterior regions. The FL-PL and flexural deflection value at the 100-N loading point of the reinforced maxillary denture specimens were tested. Results. All of the reinforced dentures had a higher FL-PL than the denture without reinforcement but the FL-PL values of all the dentures were not significantly different from each other. The efficiency of the FRC reinforcement compared to the unreinforced denture was 1.54–1.75 times greater. All of the reinforced dentures showed significantly lower deflection compared to the unreinforced denture, but the flexural deflections of all the dentures were not significantly different from each other. Conclusions. The location of the FRC reinforcement did not affect the fracture resistance of the maxillary acrylic resin complete denture. All of the reinforced dentures had higher FL-PL and lower flexural deflection than the denture without reinforcement.

OS13-1-3 Tensile Properties and Viscoelastic Model of Resin Thin Film

This paper presents tensile properties of a polyimide thin film used in electronic devices. Tensile tests were performed to determine Young's modulus, proportional limit, yield stress, ultimate tensile strength and elongation of the polyimide film. Effects of strain rate and temperature on the tensile properties were discussed. There was a little effect of strain rate on Young's modulus but proportional limit, yield stress and ultimate tensile strength increased with increasing strain rate. Only elongation decreased with strain rate. Young's modulus, proportional limit, yield stress and ultimate tensile strength decreased with increasing temperature, but elongation increased. Applicability of a viscoelastic model for describing the stress-strain curves of the polyimide film was discussed.

PROPORTIONAL LIMIT AND VISCOELASTICITY OF WOOD

Compression tests of Japanese cedar in its L, R, and 45-degree directions under various stress rates were done in order to investigate the viscoelastic effect on the stress-strain curves with a focus on the proportional limit. The tangent modulus decreased gradually with the elevation of stress either for any direction of loading to the grain and for any stress rate of slow to fast loading. This suggests that the so-called proportional limit does not exist in an exact sense. A three-element model interpreted the viscoelasticity of the tested wood such that the spring constant is free from stress rates as well as stress repetitions like the Hookean body, while the dashpot is sensitive to them unlike the Newtonian linear fluid.

Effect of recycled poly(ethylene terephthalate) content on properties of extruded poly(ethylene terephthalate) sheets

Sixty (60) polyethylene terephthalate (PET) sheets containing 0—100% recycled-PET (RPET) bottle flake were produced using industrial extruders. The PET/RPET sheets were characterized using differential scanning calorimetry, ultraviolet— visible spectroscopy, mechanical testing, and inductively coupled plasma—atomic emission spectroscopy (ICP—AES). The absorbance at 350 nm, %crystallinity, crystallization temperature, and crystallization peak offset were found to be both unaffected by a silicone mold release coating and reasonably valid indicators of %RPET. Mechanical testing determined that incorporating recycled content into virgin resin will significantly alter the composite mechanical properties; analysis indicated that there was approximately a 2-, 3-, and 30-MPa increase in stress at the proportional limit, stress at yield, and Young’s modulus, respectively, in the machine direction at 40% RPET concentration when compared to virgin resin. The ICP—AES determined that PET/RPET sheets can be safely used for food packaging as according to California Health and Safety Code.

Tensile Properties of Polyamide Thin Films for Electronic Devices

This paper presents the results of tensile properties of four kinds of polyamide thin films with different contents of filler used in electronic devices. Tensile tests were performed to determine Young's modulus, proportional limit, yield stress, ultimate tensile strength and elongation of polyamide thin films. The Young's modulus of polyamide films increased with increasing the contents of filler, and the trend of the data was satisfactory simulated by the Kerner model. The polyamide film with 42% filler showed the largest proportional limit, yield stress and ultimate tensile strength. The elongation decreased with increasing the contents of filler. The most suitable filler content was around 40% from considering the coefficient of thermal expansion and mechanical properties of the films.

3256 Development of Partially Ni-coated Diamond Abrasives for Electroplated Tools

Electroplated diamond tools with superior proportional limit and wear resistance are developed for grinding hard and brittle materials. Application of Ni-coated diamond abrasives is effective for high-speed manufacturing of electroplated grinding tools. However, the sharpness of the grinding tool decreases because nickel membrane was attached on the surface of abrasives. The phenomenon of abrasives aggregation is also serious. In this study, we developed partially Ni-coated diamond abrasives. The production method of the partially Ni-coated abrasives was described and the effect of application of the abrasives was investigated. As the results, the problems with using Ni-coated abrasives or non-coated abrasives could be solved and the grindability of electroplated tools was improved.

Bending Properties of Medium-Density Fiberboard and Plywood Obtained by Compression Bending Test

Compression bending testing, as described in this article, has been used successfully on various advanced composite materials, such as carbon-fiber reinforced plastics, to compute bending properties. This method might be applicable for several wood-based panels, such as medium-density fiberboard (MDF) and plywood, because they are quite thin, and thus the elastica phenomena can be easily induced. In this study, the bending properties of MDF and Lauan five-ply wood were determined by performing a compression bending test. The validity of the compression bending testing was then examined by comparing these results with the results from flexural vibration tests and three-point bending tests. The compression bending test proved effective for measuring the flexural Young's modulus when the length/thickness ratio was larger than 33 because the test method minimizes deflection caused by shearing force. Nevertheless, it was even less effective when the length/thickness ratio was smaller than 33. It was expected that the test would be more effective than the three-point bending test for measuring proportional limit stress and bending strength because the test specimen is independent of the stress concentration around the loading nose; however, this proved not to be the case for the materials investigated in this study. Thus, further research is still needed to devise ways to more effectively measure the bending properties of the materials tested.

Cyclic fatigue properties of cobalt-chromium alloy clasps for partial removable dental prostheses

Cast cobalt-chromium (Co-Cr) alloy clasps have been widely used for prosthodontic treatment, but long-term retentiveness of these clasps is not clear. The purpose of this study was to investigate the residual retentive force of 3 types of cast Co-Cr alloy clasps in relation to their proportional limits. Thirty half-round straight clasps and 30 circumferential clasp assemblies were made from 3 Co-Cr alloys (Hardalloy, Regalloy, and Vera PDN) (n=10). All of the straight clasps were subjected to a compression-deformation test to obtain data for displacement/load at the proportional limit. Two undercut depths (0.25 mm and 0.50 mm, n=5) were included in a cyclic fatigue test. Each circumferential clasp assembly was subjected to an insertion/removal test on a metal abutment tooth for 7200 cycles to simulate 5 years of clinical use. The residual retentive force was measured after 360 cycles; thus, the retentive force of each clasp was recorded 21 times throughout the test. The data were subjected to repeated-measures ANOVA (α=.05) to compare the retentive force of each group of clasps for different periods of fatigue testing. The ANOVA. The Student t test (α=.05) was used for analysis of clasps fabricated with the same alloy but with different undercuts. A linear correlation analysis (α=.05) was used to test the correlation between retentive forces and cycling sequences. The mean values of displacement at the proportional limit for the 3 Co-Cr alloys varied from 0.30 mm to 0.36 mm. The mean retentive forces of each alloy group decreased dramatically after the first cycling phase (P<.05). Thereafter, the decrease was more gradual but was still significantly different compared to the original retentive forces (P<.05). Compared to clasps in the 0.25-mm undercut group, those in the 0.50-mm undercut group exhibited greater mean retentive forces before the cyclic fatigue test (P<.05), as well as a greater decrease in the retentive force at the end of the test (P<.05). A negative correlation was found between the retentive force of cast Co-Cr alloy clasps and the logarithm of cycling sequences. After a test simulating 5 years of service, cast Co-Cr alloy clasps exhibited a residual retentive force to satisfy the requirements for clinical use.

Failure of Flawed Utility Poles in Wind Gusts

The purpose of this study is to account for failures of wood utility poles in wind storms based on dynamic analysis and pole imperfections. The utility pole supporting multiple overhead transmission lines is modeled as a uniform Bernoulli–Euler cantilevered beam fixed at the base and subjected to three types of suddenly applied transverse loads that simulate a wind gust: a uniform pole pressure, a point load at the tip accounting for line and transformer drag, and another point load near midlength, accounting for drag on lines strung from that location. The dynamic pole moments are based on normal mode calculations rather than static calculations with a dynamic impact factor, and the critical flexural stresses include stress concentrations arising from pole imperfections such as holes, knots, and surface gouges. A case study illustrates the results for one of about 400 failed wood poles downed in a single New Jersey storm in 2003 with 107 km/h (67 m/h) wind gusts. Here, the critical pole stress based on the dynamic model and a hole imperfection exceeded the proportional limit stress of the wood. The predicted dynamic stresses are higher than those based on the National Electrical Safety Code.

Compressive Strength of Diamond from First-Principles Calculation

Compressive strength, like tensile and shear strength, is one of the intrinsic mechanical properties of solid materials. We investigated the ideal compressive strength and corresponding compressive deformation of diamond using pseudopotential density functional theory. The calculated uniaxial compressive strength of diamond is −223.1, −469.0, and −470.4 GPa along the ⟨100⟩, ⟨110⟩, and ⟨111⟩ directions, respectively. The elastic deformation of diamond in compressive strain below the proportional limit of 17% has been determined from the perfect linear response between strain and stress along the ⟨100⟩ direction. The present work should be helpful to the understanding of the compressive property of diamond and to the explanation of the limit strength of diamond anvil cell.

Mechanical properties of injection-molded thermoplastic denture base resins

Objective. To investigate the mechanical properties of injection-molded thermoplastic denture base resins. Material and methods. Four injection-molded thermoplastic resins (two polyamides, one polyethylene terephthalate, one polycarbonate) and, as a control, a conventional heat-polymerized polymethyl methacrylate (PMMA), were used in this study. The flexural strength at the proportional limit (FS-PL), the elastic modulus, and the Charpy impact strength of the denture base resins were measured according to International Organization for Standardization (ISO) 1567 and ISO 1567:1999/Amd 1:2003. Results. The descending order of the FS-PL was: conventional PMMA > polyethylene terephthalate, polycarbonate > two polyamides. The descending order of the elastic moduli was: conventional PMMA > polycarbonate > polyethylene terephthalate > two polyamides. The descending order of the Charpy impact strength was: polyamide (Nylon PACM12) > polycarbonate > polyamide (Nylon 12), polyethylene terephthalate > conventional PMMA. Conclusions. All of the injection-molded thermoplastic resins had significantly lower FS-PL, lower elastic moduli, and higher or similar impact strength compared to the conventional PMMA. The polyamide denture base resins had low FS-PL and low elastic moduli; one of them possessed very high impact strength, and the other had low impact strength. The polyethylene terephthalate denture base resin showed a moderately high FS-PL, moderate elastic modulus, and low impact strength. The polycarbonate denture base resin had a moderately high FS-PL, moderately high elastic modulus, and moderate impact strength.

Microstructural Analysis and Mechanical Properties of Pb(Zr,Ti)O3 Fibers Derived by Different Processing Routes

Piezoceramic fibers are broadly used for advanced ultrasound transducers and composite sensors and actuators for smart system applications. Different techniques (ALCERU® cellulose spinning technique, extrusion, and polysulfone process) have been developed for fiber fabrication, although there is still an essential need to evaluate the mechanical and electromechanical performance of these fibers. In this study, the microstructure and mechanical properties have been investigated for different fibers fabricated by the three routes. Because of the same sintering program, the fibers showed mainly a similar grain size (1–2 μm) and porosity (2%–6%). A tensile strength up to 72 MPa could be measured for PZT fibers with a diameter of 250 μm produced by the cellulose spinning technique. The Young's modulus varied between 30 and 60 GPa. Stress–strain deformation showed nonlinearity behavior, which could be attributed to ferroelastic domain switching. The threshold for domain switching (proportional limit) of the deformation curve had decreased by increasing the diameter of the fiber. No correlation between fiber processing and proportional limit could be observed.

The use of recycled metal in dentistry: Evaluation of mechanical properties of titanium waste recasting

Environmental concerns are increasing rapidly, and the public and industry are concerned about natural resources. The products are produced to meet the customer's demand as to quality. However, today it is equally important to take into account cost, ecological factors in production and recycling of products. The same way, the dentistry must contribution with a recasting the alloys used to rehabilitation oral. This study evaluated the effect of the condition of Ti (as-received and re-cast) on its mechanical properties, microstructure and fractography. Castings ( n = 6) with Ti in the as-received and once recast condition were made in a centrifugal casting machine using a high-purity argon gas. The ultimate tensile strength (UTS), proportional limit (PL) and elongation (EL) of the as-received specimens were evaluated in a universal testing machine at a crosshead speed of 1 mm/min. The fractured specimens were polished down for Vicker's microhardness (VHN) measurement (100 g/15 s) from 25 μm below the cast surface, then at depths of 50, 100, 200 and 500 μm. The microstructures of the alloys were also revealed. Scanning electron microscopy fractography was undertaken for the fractured surfaces after testing. The data from the mechanical tests and hardness were subjected to the Student's t-test and two-way repeated measures ANOVA, respectively. Tukey's test was used for pairwise comparison ( α = 0.05). Higher UTS, PL and VHN and lower EL were observed for recast cp Ti. The microstructure was not influenced by recasting, but the mode of fracture was. The use of the recasting procedure can lower the costs of cp Ti castings and can be safely in dentistry.

On the Mutual Interactions of Monotonic and Cyclic Loading and their Effect on the Strength of Aluminium Alloys

The paper investigates the interaction of monotonic cyclic loading and their effect on the yield strength of aluminium alloy. Two different loading combinations were considered, i.e. torsion-reverse-torsion superimposed on monotonic tension and monotonic torsion combined with tension-compression cycles. All strain controlled tests were carried out at room temperature using thin-walled tubular specimens. The maximum value of the total cyclic strain amplitude was less than 1%. The influence of amplitude, frequency and shape of cyclic loading signal on the proportional limit and conventional yield point was investigated. The experimental results presented in the paper may be useful to designers of structures that utilize manufacturing processes such as drawing, extrusion, forging of selected semi-finished elements or researchers working on the development of new constitutive equations.

Cracking Resistance of Silicon Carbide Composites by Single‐ and Double‐Notched Specimen Techniques

This paper aims to evaluate fracture resistance of nanoinfiltration transient eutectic phase‐sintered (NITE)–silicon carbide fiber‐reinforced silicon carbide matrix (SiC/SiC) composites, using the single‐edge notched bend (SENB) test and the double‐notch tensile (DNT) test. Both SENB and DNT test results identified notch insensitivity of NITE–SiC/SiC composites. With the fact of notch insensitivity, unique proportional limit stress, and fracture strength were identified regardless of the presence of artificial notches. By applying the nonlinear fracture mechanics, micro‐ and macrocracking energies were separately estimated. Specifically, lower microcrack formation energy was identified compared with conventional low‐stiffness composite system. Finally, superior crack resistance of NITE–SiC/SiC composites was clearly demonstrated.

Osteoplastic Biomaterials and Their Physical and Mechanical Properties

Objective. To perform comparative study of composition and strength properties of osteoplastic biomaterials subjected to technological processing. Material and Methods. Specimens of native (initial) and deproteinized bone tissue were analyzed. Strength properties of specimens were studied by single-axis static extension with automatic recording of load curves. Load-extension curves were used to calculate mechanical parameters: proportionality limit, strength limit, relative deformation before destruction, and the Young’s module. Dependence between a processing type and changes in the surface morphology, element composition, overall dimensions, and dry weight of specimens was identified. Results. All bone tissue specimens had small amount of deformation typical for fragile materials – 1 %. Proportionality limit for native bone tissue was 27 MPa, and that for deproteinized tissue –29 MPa. Strength limit did bone on the type of chemical processing of tissue and had the value of 80–90 MPa. Collagen presence influenced the Young’s module which was 110 MPa in deproteinized bone tissue, two-fold decreased from that in initial bone tissue (230 MPa). Topography of specimens and fracture surfaces were more pronounced after deproteinization. Conclusion. The study of physical and mechanical properties and composition of compact bone specimens gives an understanding of processing type influence on bone tissue structure and properties.

Slenderness classification of unstiffened metal plates under shear loading

Buckling behavior of slender and compact carbon steel, stainless steel and aluminum plates under the action of in-plane shear is investigated. Unstiffened shear plates with respect to their slenderness parameter and buckling behavior are qualitatively and quantitatively divided into slender, moderate and stocky categories. Accordingly, slender plates have a low buckling capacity, followed by a large postbuckling reserve. Their ultimate load coincides with the formation of inclined yield bands. Stocky plates yield before buckling. They have some post-yield capacity, buckle plastically and their ultimate and critical loads are equivalent. Moderate plates have concurrent material yielding and geometrical buckling followed by a sudden loss of stiffness. They neither have post-yield nor postbuckling reserves. Since the proportional limit stress is observed to be the cause of bifurcation in stocky plates, it is suggested that in dealing with the slenderness parameter, the yield stress be replaced by the proportional limit stress.