Proportional Limit Research Articles

Development of Electroformed Diamond Tool Strengthened by Synthesized Intermetallic Alloy

An electroformed diamond tool with superior proportional limit and wear resistance was developed for the microgrinding of hard and brittle materials, in which a tool of small diameter is rotated at a high speed. A plating rig that can fabricate an electroformed diamond tool with fine diamond grains and an electrodeposited Ni grain size less than 2 nm was newly developed. A thermal etching for roughening diamond grain surfaces was conducted to increase gripping strength between diamond grains and the bond material Ni of the tool. In addition, an annealing process to synthesize the intermetallic alloy Ni3P was used on the tool not only to increase the hardness of the bond material but also to increase the proportional limit of the tool. It was verified through the bending test that both the Young's modulus and proportional limit of the tool increased to about 40 GPa and 1.5 GPa, respectively, using thermally etched diamond grains and annealing tools, compared with those of electroformed diamond tools fabricated using conventional techniques.

POST-THERMAL TREATMENT OF ORIENTED STRANDBOARD (OSB) MADE FROM CYPRESS (CUPRESSUS GLAUCA LAM.)

The objective of this research was to determine the physical and mechanical properties of oriented strandboard (OSB) using strands of Cupressus glauca Lam., before and after a thermal treatment, as well as to evaluate the susceptibility of the boards to fungi attack. Boards with nominal density of 0.70 g/cm 3 were produced with 5% and 8% of urea-formaldehyde (UF) resin. Physical and mechanical properties were evaluated according to ASTM D 1037 (1991) standard and compared with CSA O437.0 and ANSI A.208.1 standards. All mechanical properties were higher than those values required by both standards, except the modulus of elasticity in parallel axis. The thermal treatment slightly reduced the modulus of elasticity and stress at proportional limit, both in perpendicular axis, however improved significantly dimensional stability. Dimensional stability of the treated OSB was improved at the lower resin level but did not reach the maximum value required by the Canadian standard. Biological assay showed that heat-treated cypress OSB exposed to P. sanguineus reduced mass loss from 39% to 50%, while for G. trabeum the reduction was from 40% to 49%. Post thermal treatment of manufactured OSB (190oC, 720 s) can be the recommended method to reduce the hygroscopicity without great effect on mechanical properties and to protect panels against these fungi.

Deformability and strengh of expanded polystyrene (EPS) under short-term shear loading

Data obtained in investigating the ultimate strength and deformability of expanded polystyrene under short-term shear loading according to EN 12090 are discussed. Linear regression equations are used for describing the ultimate shear strength and modulus in relation to the density of EPS. A correlation is found to exist between the ultimate strength of EPS and its density and specimen thickness. An empirical dependence between the shear modulus and density of EPS is established. The strains corresponding to the conditional limit of proportionality and to the ultimate shear strength of EPS in short-term loading are determined.

ＳＮＣＭ６３０鍛鋼材の疲労強度特性

Axial fatigue tests of SNCM630 forgings, which are often used for high-strength components in diesel engines, have been carried out with various stress ratios (R) for fatigue life N≤107 cycles. S-N curves obtained from the experimental results have shown fatigue limits of 500, 400, 300 and 190 MPa for R=-1, 0, 0.3 and 0.6, respectively. The results suggest that the fatigue strength of SNCM630 is highly improved from a similar material, SNCM439. Study on the effect of stress ratio using a fatigue limit diagram with failure probability shows that modified Goodman diagram is applicable for the determination of fatigue strength of this material. However, under a stress condition of high R where the maximum applied stress may exceed the proportional limit, as for in the design it is recommended that the applied stress will not exceed the proportional limit. SEM observations of the fracture surfaces have revealed that fatigue cracks initiated from subsurface inclusions which are identified as alumina particles of 35μm in diameter in only two specimens while crack initiated from surface flaws in other samples. Using the √area parameter model for internal defects, the fatigue limit for N>109is estimated as approximately 410 MPa in case of R=-1.

가속도계를 이용한 재료의 영계수 측정방법

For the description of the elastic properties of linear objects a convenient parameter is the ratio of the stress to the strain, a parameter called the Young's modulus of the material. Young's modulus can be used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material. Conventional method for estimating Young's modulus measured the ratio of stress to corresponding strain below the proportional limit of a material using a tensile testing machine. But the method needs precision specimens and expensive equipment. In this paper, we proposed method for estimating Young's modulus using accelerometer. The basic idea comes from that the wave velocity is different as the Young's modulus. To obtain Young's modulus, a group velocity is obtained. It is difficult to measure group velocity. This is because plate medium has a dispersive characteristics which has different wave speed as frequency. In this paper, we used Wigner-Ville distribution to measure group velocity. To verify the proposed method, steel and acryl plate experiments have been performed. Experimental results show that the proposed method is powerful for estimating Young's modulus.

Interspecific variation in beeswax as a biological construction material

Beeswax is a multicomponent material used by bees in the genus Apis to house larvae and store honey and pollen. We characterized the mechanical properties of waxes from four honeybee species: Apis mellifera L., Apis andreniformis L., Apis dorsata L. and two subspecies of Apis cerana L. In order to isolate the material effects from the architectural properties of nest comb, we formed raw wax in to right, circular cylindrical samples, and compressed them in an electromechanical tensometer. From the resulting stress-strain curves, values for yield stress, yield strain, stress and strain at the proportional limit, stiffness, and resilience were obtained. Apis dorsata wax was stiffer and had a higher yield stress and stress at the proportional limit than all of the other waxes. The waxes of A. cerana and A. mellifera had intermediate strength and stiffness, and A. andreniformis wax was the least strong, stiff and resilient. All of the waxes had similar strain values at the proportional limit and yield point. The observed differences in wax mechanical properties correlate with the nesting ecology of these species. A. mellifera and A. cerana nest in cavities that protect the nest from environmental stresses, whereas the species with the strongest and stiffest wax, A. dorsata, constructs relatively heavy nests attached to branches of tall trees, exposing them to substantially greater mechanical forces. The wax of A. andreniformis was the least strong, stiff and resilient, and their nests have low masses relative to other species in the genus and, although not built in cavities, are constructed on lower, often shielded branches that can absorb the forces of wind and rain.

Time-Related Procedure to Structural Column Failure

Based on a thought experiment, a slender column is loaded to the Euler column buckling load by bringing the platen of a testing machine down at a uniform rate. The shortening of the column y is proportional to the time t. Bending, that is, bowing out of the column, starts as soon as the compressive load P > 0. Every column to be tested has an initial accidental eccentricity, either because it is not perfectly straight or the mean resistance internally of the random arrangement of the crystalline structure of the grains of structural steel (or other metal) does not coincide with the central column axis. For a solid rectangular cross-section, the eccentricity e falls within a certain interval. The value of e is always greater than zero, but also has an upper bound so that the maximum compressive stress due to compression plus bending does not exceed the proportional limit σ pl . Euler's formula for critical buckling P cr when divided by the cross-sectional column area A does not yield a meaningful average stress. Only the maximum compressive fiber stress, at the midlength of the column is significant as it approaches σ pl . The coordinates of the bowed column are solved for at any time t at the column midlength, until the column fails at time t cr . It is also demonstrated that P = f(y) is not a straight line, although it may come close. Adopting a convenient rate of compression of the column C 1 the time to failure t cr can also be predicted for the corresponding, computed y cr .

The effect of temperature on viscoelastic properties of glass ionomer cements and compomers

The objective of this study was to determine the viscoelastic properties of different types of glass ionomer cements (GICs) and compomers under varying temperature conditions found in the mouth. The materials tested were a conventional GIC (Aqua Ionofil U), a resin modified GIC (Fuji II LC), a highly viscous GIC (Voco Ionofil Molar), and two polyacid modified composite resins/compomers (Glasiosite and Dyract Flow). Six groups of four specimens were prepared from each material. One group was stored dry for 24 h and was subsequently tested dry at 21 degrees C. Each of the remaining five groups was stored for 24 h in distilled water at the temperatures 21, 30.5, 37, 43.5, and 50 degrees C, respectively, and was subsequently tested at that temperature. Shear storage modulus and loss tangent were determined by conducting dynamic torsional loading. Static shear moduli were determined by applying a constant torque (below the proportional limit of the materials) for 10 s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's test (alpha= 0.05). It was found that the viscoelastic properties varied significantly (p < 0.05) across the different materials. The compomer Glasiosite, with the highest filler content, and the highly viscous GIC Voco Ionofil Molar exhibited the highest elastic moduli and lowest loss tangents. Viscoelastic properties varied also significantly (p < 0.05) with temperature levels, but changes in the tested region were not indicative of a glass transition. Dynamic shear storage moduli were highly correlated to the static ones. Storage in water lowered the values of elastic moduli.

Buckling of laser-welded sandwich panels. Part 1: Elastic buckling parallel to the webs

This is the first of three companion papers that examine the elastic buckling and collapse of laser-welded sandwich panels with an adhesively bonded core and uni-directional vertical webs. In compression parallel to the webs, the face sheet in between two webs can be treated as a long rectangular plate supported at the sides and resting on a continuous elastic foundation. Using a generalized form of the Kirchoff equation, the plate buckling load is evaluated for a Winkler and Pasternak foundation, and for a foundation model where the core is characterized by an elastic half-space. Although the elastic half-space model is most sophisticated in the way that the decay of transverse stress through the core is described, it requires that the buckling load is calculated iteratively and is therefore not suitable for engineering applications. In contrast, the Pasternak foundation model is able to demonstrate the effect of different boundary conditions at the laser weld and different core properties by the variation of a simple clamping factor and two foundation moduli. By changing the clamping factor, the model can be used to describe plate buckling as well as wrinkling, and, by varying the foundation moduli, it is possible to distinguish between symmetrical and anti-symmetrical buckling modes. Evaluation of the buckling solution shows that, for low modulus core materials, the plate buckling strength is determined only by the boundary conditions at the laser weld, while for high modulus materials anti-symmetrical wrinkling dominates. To improve the accuracy of the solution for non-standard configurations, the foundation moduli are calibrated using the elastic half-space model and finite element results as a reference. It is found that, by using a smaller Winkler foundation modulus, the accuracy and consistency of the Pasternak model are improved considerably. However, the results also show that, for current sandwich configurations, the proportional limit of the face plate material is usually reached well before elastic buckling occurs. All experimental work is therefore delegated to the third paper, which deals with extension of the Pasternak foundation model into the elasto-plastic regime and non-linear finite element modelling.

Buckling of laser-welded sandwich panels. Part 2: Elastic buckling normal to the webs

This is the second of three companion papers that examine the elastic buckling and collapse of laser-welded sandwich panels with an adhesively bonded core and uni-directional vertical webs. In the first paper, it has been shown that the critical load in compression parallel to the webs can be accurately predicted by using a Pasternak foundation to model the core and by using a simple clamping factor to describe the boundary conditions at the laser weld. In this paper, the same model is adapted to predict the critical load in compression normal to the webs. As the face plate is now short and wide, rather than long and narrow as before, a ‘constrained wrinkling’ approach is outlined that recognises that the face plate is limited in its ability to wrinkle naturally and can only deform in certain mode shapes. The clamping factor and the effective wave length are derived for different buckling mode shapes and boundary conditions at the laser weld, and the constrained wrinkling load is determined by evaluating the buckling load for successive modes and simply picking the smallest value. It is shown that, for low modulus core materials, the constrained wrinkling load is equal to the bare plate buckling load and, for high modulus materials, the solution converges toward anti-symmetrical wrinkling, as has been found for the case of compression parallel to webs. The constrained wrinkling load agrees well with finite element results but as before the proportional limit of the face plate material is usually reached well before elastic buckling occurs.

An experimental investigation of humidity and temperature effects on the mechanical properties of perfluorosulfonic acid membrane

The mechanical properties of a perfluorosulfonic acid (PFSA) membrane have been investigated at different humidities and temperatures in a custom-designed environmental chamber. Tensile tests were conducted to determine Young's modulus, the proportional limit stress (“yield strength”), break stress, and break strain. In-plane dimensional changes of the membrane at different temperature and humidities were also determined. The results indicate that Young's modulus and the proportional limit stress of the PFSA membrane decrease as humidity and temperature increase. Higher temperature leads to lower break stress and higher break strain. However, humidity has little effect on the break stress and break strain. A nonparametric statistical analysis, Kruskal–Wallis test, is applied to the experimental results, which shows that the effects of temperature and humidity on Young's modulus and proportional limit stress are statistically significant.

Cumulative Clamp Load Loss Due to a Fully Reversed Cyclic Service Load Acting on an Initially Yielded Bolted Joint System

The amount of clamp load loss due to a fully reversed cyclic service load is determined for a bolted assembly in which the fastener and the joint were both tightened initially beyond their respective proportional limits. The cyclic reversed load acts in a direction parallel to the bolt axis. During the first half of each cycle, the cyclic load acts as tensile separating force that increases the fastener tension further into the nonlinear range; it simultaneously reduces the joint clamping force. Thus, after the first one half of the cycle, the clamp load is reduced from its initial value due to the plastic elongation of the fastener. During the second half cycle, the cyclic load compresses the joint further into the plastic range; simultaneously, it reduces the fastener tension. Due to the permanent set in the compressed joint, the clamp load is decreased further at the end of the second half cycle of the service load. The cumulative clamp load loss due to the permanent set in both the fastener and the joint is analytically determined using a nonlinear model. Variables investigated in this study include the joint-to-fastener stiffness ratio, the ratio of the initial fastener tension to its elastic limit, and the ratio of the external force to its maximum tensile value that would trigger joint separation.

Effect of relining, water storage and cyclic loading on the flexural strength of a denture base acrylic resin

This study investigated the effect of relining, water storage and cyclic loading on the ultimate flexural strength (FS(U)) and on the flexural strength at the proportional limit (FS(Pl)) of a denture base acrylic resin (Lucitone 550-L). Rectangular bars of L were made (64 mm x 10 mm x 2 mm) and relined (1.3mm) with four relining resins (Kooliner-K, Ufi Gel Hard-UGH, Tokuso Rebase Fast-TR and New Truliner-NT). In addition, specimens relined with L and intact L specimens were made (64 mm x 10 mm x 3.3 mm). A three-point flexural test was applied on the specimens (n=10) after (1) polymerization; (2) water storage (30 days); (3) cyclic loading (10,000 cycles at 5 Hz) and (4) water storage (30 days)+cyclic loading. Data (MPa) were analyzed with three-way ANOVA and Tukey's HSD tests (alpha=0.05). To test for a possible correlation between FS(U) and FS(Pl), a linear regression coefficient "r" was calculated. After water storage, L-UGH and L-TR demonstrated an increased FS(U) (41.49-50.64 MPa and 49.95-57.36 MPa, respectively) (P<0.05). Only L-TR demonstrated an increased FS(Pl) (20.58-24.21 MPa) after water storage (P<0.05). L-L had the highest FS(U) (between 78.57 and 85.09 MPa) and FS(Pl) (between 31.30 and 34.17 MPa) (P<0.05). The cyclic loading decreased the FS(U) and FS(Pl) of all materials (P<0.05). Regression analysis showed a strong linear correlation between the two variables (r=0.941). Water storage improved the FS(U) of L-UGH and L-TR and the FS(Pl) of L-TR. L-L produced the highest FS(U) and FS(Pl). The FS(U) and FS(Pl) of all materials were detrimentally influenced by cyclic loading.

Mechanical properties of pure Ni and Ni-alloy substrate materials for Y–Ba–Cu–O coated superconductors

Mechanical properties of rolling-assisted, biaxially-textured substrates (RABiTS) and substrates for ion-beam assisted deposition (IBAD) coated superconductors are measured at room temperature, 76, and 4 K. Yield strength, Young’s modulus, and the proportional limit of elasticity are determined, tabulated and compared. Results obtained are intended to serve as a database of mechanical properties of substrates having the same anneal state and texture as those incorporated in the general class of RE–Ba–Cu–O coated conductor composites (RE = rare earth). The RABiTS materials measured are pure Ni, Ni–13at.%Cr, Ni–3at.%W–2at.%Fe, Ni–10at.%Cr–2at.%W, and Ni–5at.%W. The IBAD substrate materials included Inconel 625 and Hastelloy C-276. The Ni alloys are substantially stronger and show higher strains at the proportional limit than those of pure Ni. Substrates fully coated with buffer layers, ≈1 μm of Y–Ba–Cu–O, and 3–5 μm of Ag have similar mechanical properties (at 76 K) as the substrate alone. Somewhat surprisingly, plating an additional 30–40 μm of Cu stabilizer onto high-yield-strength (690 MPa) Hastelloy coated conductors ∼100 μm thick, reduces the overall yield strength of the composite structure by only about 10–12% at 76 K and 12–14% at room temperature; this indicates that the Cu layer, despite its relatively soft nature, contributes significantly to the overall strength of even high-strength coated conductors.

Tensile deformation behavior of plasma-sprayed Ni–45Cr coatings

Deformation behavior of plasma-sprayed Ni–45Cr coatings was studied in terms of stress–strain relation and modulus changes under tensile loading. The tensile loading was applied in both directions parallel and perpendicular to the lamellar plane of the coatings. The influences of spray distance on Young's modulus and Poisson's ratio of the coatings were investigated. The Young's modulus was measured from both directions parallel and perpendicular to the lamellar plane. Results showed a linear relation between the stress and strain in the direction parallel to the lamellar plane. The similar linear stress–strain relation in the direction perpendicular to the lamellar plane was revealed only when the tensile loading with up to a certain value was applied, while a nonlinear stress–strain relation prevailed under a higher tensile load. The increase of the proportional limit of the coating was observed under repetitive tensile loading perpendicular to the lamellar plane. The modulus measured from the direction parallel to the lamellar plane changed from 78 GPa to 92 GPa. Spray distance showed minor effect on the Young's modulus. Moreover, the modulus measured from the direction perpendicular to the lamellar plane, changing from 48 GPa to 64 GPa, was lower than that obtained from the direction parallel to the lamellar plane. It is clear that plasma-sprayed metallic coating presented an anisotropic elastic behavior. In addition, it was found that the coatings yielded a Poisson's ratio of 0.13–0.15 which is lower than that of bulk materials. Spray distance also has no significant influence on the Poisson's ratio of coatings.

Efeitos da ovariectomia experimental no metabolismo ósseo de ratas wistar adultas: um modelo para estudo da osteoporose

A privação dos hormônios ovarianos acarreta distúrbios endócrinos e funcionais, tais como disfunção sexual, perda da libido, maior risco de osteoporose e de doenças cardíacas, níveis alterados de lipoproteínas, ganho ponderal, entre outros. A osteoporose é uma patologia óssea sistêmica caracterizada por um desequilíbrio entre reabsorção e formação óssea, resultando em um aumento da fragilidade óssea. O objetivo do nosso estudo foi descrever os efeitos da ovariectomia (OVT) experimental no metabolismo ósseo e no ganho ponderal de ratas wistar adultas. Ratas adultas foram submetidas ao procedimento de OVT (G1) bilateralmente ou uma falsa castração (G2). Após 30 dias, foi coletado sangue para dosagem de estrogênio sérico e após 60 dias os animais foram sacrificados para a realização das análises séricas e ósseas. O consumo de ração e o ganho de peso foram monitorados duas e uma vez por semana, respectivamente. As ratas OVT apresentaram médias estatisticamente maiores (p &lt; 0,05) para o consumo de dieta, ganho de peso e atividade sérica da fosfatase alcalina e, menores (p &lt; 0,05) para concentração de estrogênio sérico, conteúdo de cálcio, radiodensidade e limite proporcional ósseo quando comparadas às ratas sham-operadas. Além das análises quantitativas, as ratas OVT apresentaram fêmures com superfície com fossas de reabsorção visivelmente profundas, confirmando que ratas ovariectomizadas são um bom modelo de estudo de osteoporose em mulheres na pós-menopausa.

Influência do diâmetro e do ângulo de inserção sobre a resistência à tração de âncoras rosqueadas

Foi avalida a resistência à avulsão de âncoras rosqueadas de 3,5 e 4,5 mm de diâmetro, utilizando fêmores de suínos frescos congelados como modelo e uma máquina universal de ensaios. O trocânter maior era ressecado e as âncoras, montadas com um cabo de aço flexível para permitir a fixação na máquina de ensaio, eram inseridas no osso esponjoso próximo à borda da cabeça femoral, a 30°, 60° e 90° com o eixo longitudinal da diáfise femoral. Os espécimes eram fixados na máquina de ensaio e a tração era aplicada continuamente, à razão de 1 mm/minuto até que ocorresse a falha da montagem. Dados referentes à carga máxima aplicada, carga no limite da proporcionalidade, rigidez e resiliência foram registrados e comparados (p&lt;0.05). Os resultados mostraram que a carga máxima, a carga no limite da proporcionalidade e a resiliência foram significantemente maiores (p=0,04, p=0,01 e p=0,02, respectivamente) para as âncoras de 4,5 mm de diâmetro inseridas a 60°, comparado aos outros ângulos e às âncoras de 3,5 mm em qualquer ângulo. Carga no limite da proporcionalidade e rigidez não diferiram significantemente para as âncoras de ambos os diâmetros e os diferentes ângulos de inserção.

生体用Ti-XNb-10Ta-5Zr合金の引張変形挙動解析

Ti-XNb-10Ta-5Zr alloys were fabricated based on Ti-30Nb-10Ta-5Zr alloy, which was the composition that simplified that of Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications. The tensile deformation mechanisms of the Ti-25Nb-10Ta-5Zr, Ti-30Nb-10Ta-5Zr, and Ti-35Nb-10Ta-5Zr alloys were investigated using X-ray diffraction analysis under several loading conditions. Under loading conditions, the X-ray diffraction peaks of all specimens in this study shift to higher angles than those obtained under non-loading conditions. In the crystal orientation of Ti-30Nb-10Ta-5Zr alloy, in which the lattice strain has reached the maximum elastic lattice strain, plastic deformation (for example slip) is moved with elastic deformation. Therefore, the elastic modulus of this alloy appears to decrease in terms of strain over a proportional limit. Thus, the elastic deformation behavior of the Ti-30Nb-10Ta-5Zr alloy does not obey Hooke's law.

Evaluation of Fiber/Matrix Interfacial Strength of Neutron Irradiated SiC/SiC Composites Using Hysteresis Loop Analysis of Tensile Test

Advanced SiC/SiC composites composed of highly-crystalline and near-stoichiometric SiC fibers, SiC matrix by CVI method, and PyC interphase were irradiated up to 1:0 � 10 25 n/m 2 (E > 0:1 MeV, � 1 dpa) at 1273 K. Unload/reload cyclic tensile test and hysteresis loop analysis were carried out in order to identify neutron irradiation effects on interfacial properties of advanced SiC/SiC. The composites exhibited good irradiation resistance in ultimate tensile strength (� 10% increase), but there were slight reduction of elastic modulus and proportional limit stress (PLS) (� 10%). Wider hysteresis loops and lower gradient of the curves beyond PLS from the strain–stress curves, and longer pullouts of fiber from the SEM observation were observed, which imply weaker F/M interactions after neutron irradiation. From the hysteresis loop analysis, degradation of interfacial sliding stress and negative increment of misfit stress after neutron irradiation were obtained.

Nonlinear Strain Hardening Model for Predicting Clamp Load Loss in Bolted Joints

Abstract Closed form solution for the amount of clamp load loss due to an externally applied separating force is determined for a bolted assembly in which the fastener is initially tightened beyond its proportional limit. The joint may or may not have been yielded at initial assembly, however. After the initial tightening of the fastener, the joint is subsequently subjected to a tensile separating force, which further increases the fastener tensile stress into the nonlinear range. Such a separating force will simultaneously reduce the clamping force in the bolted joint. Upon the removal of the separating service load, the bolted joint system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the fastener tension is reduced from its value at initial assembly, due to the plastic elongation of the fastener. The reduction in fastener tension translates into a partial—yet permanent—loss of the clamping load, which may lead to joint leakage, loosening, or fatigue failure. A nonlinear strain hardening model is implemented in order to describe the fastener behavior past the proportional limit of its material, and to determine the clamp load loss due to the permanent set in the fastener after the separating force has been removed. In order to study the effect of strain hardening, various rates of strain hardening are used for modeling the behavior of the fastener material. The effect of three nondimensional variables on the amount of clamp load loss is investigated. This includes the joint-to-fastener stiffness ratio, the ratio of initial fastener tension to its elastic limit, and the ratio of the separating force to its maximum value that would cause joint separation to start. Analytical results are presented for a range of stiffness ratios that simulates both soft and hard joint applications.