Proportional Limit Research Articles

Evaluation of Sereni Fiber Reinforced Composite

Sereni stem fiber, due to low weight and high tensile strength was selected as backbone for graft copolymerization with binary vinyl monomeric mixture to explore its effect on percentage grafting, properties and the behavior of the modified fiber. The graft co-polymers were reinforced in a phenoplast matrix to form fiber reinforced composites and were characterized by XRD, TGA, DTA, SEM and FTIR techniques. Moisture absorbance, chemical resistance in acid and base and assessment of flexural strength, young's modulus, stress at the limit of proportionality, and hardness of the composite were studied in comparison to the phenoplast.

Isocyanate-treated cellulose pulp and its effect on the alkali resistance and performance of fiber cement composites

Abstract The impact of grafted surface of cellulose fibers on the mechanical and physical properties of fiber-cement composites (FCC) has been investigated. The grafting was performed with n-octadecyl isocyanate [i.e., with an aliphatic isocyanate (AI)], with the intention to protect the cellulose fiber from alkali degradation in the cement matrix. The chemical changes, observed by contact angle measurements and X-ray photoelectron spectroscopy, showed a higher hydrophobic character of AI-treated fibers. The strength of FCC was tested during 28 days of curing treatment. The extracted AI-treated fibers contributed to higher specific energy and final specific deflection after accelerated aging cycles in comparison with the reference composites reinforced with untreated fibers. The higher values of limit of proportionality and modulus of elasticity for composites with AI-treated fibers are an evidence of the densification of the fiber-matrix transition zone. The modulus of rupture values were higher for composites with AI-treated and Soxhlet-extracted fibers after 200 soak and dry aging cycles. In comparison with the reference, AI-treated fibers decreased the water absorption and the apparent porosity of the FCC. The modification of fibers could be a new strategy to improve the performance and stability of cement products reinforced with natural fibers.

An Investigation on the Relationship between Efficiency Monitoring and Interest Violation under Interest Assimilation

In this study, the listed electronic companies in Taiwan, from 2005 to 2010, were regarded as the research objects to investigate the relationship between efficiency monitoring and interest violation. The empirical results showed that monitoring creditors’ right is effective external monitoring power, and through compensation, directors, supervisors, and managers cozy up to one another, which causes interest assimilation. Therefore, it is suggested that a company should appropriately raise the debt ratio in order to increase the external monitoring function, and there should be a certain proportional limit for the controlling shareholders to serve as directors or supervisors in order to avoid excessive interest assimilation which further violates the interests of the minority shareholders.

Experimental and analytical study on the nonlinear bending of parallel strand bamboo beams

Parallel strand bamboo (PSB) is a new biocomposite made of bamboo strips which has superiority properties than wood products. It has been expected to be an attractive sustainable alternative for traditional structural materials. Several buildings have been constructed in China by using it as structural material in last 4years. However, the structural behavior of PSB is not nearly as well understood as conventional construction materials, which results in difficulties to predict the performances of PSB structural members. This paper aims to develop a theoretical model to predict the nonlinear flexural performances of PSB beams. The uniaxial stress–strain relationships in parallel-to-grain direction of PSB composite were firstly studied by experiments, and then 4-point bending tests for PSB beams were carried out to investigate the flexural behaviors and the damage mechanism of them. The results indicated that the tensile stress–strain relationship in parallel-to-grain direction of PSB composite exhibits linear behavior, and that the compressive one remains in linear when the stress is within the proportional limit, while becomes nonlinear, which can be simulated by quadratic polynomial, once the stress exceeds the limit. Finally, an analytical model to evaluate the bending performances of PSB beams was proposed based on experimental studies and theoretical analysis. Well agreements were achieved between the results obtained by using the proposed model and those obtained by experiments.

Different ageing conditions on cementitious roofing tiles reinforced with alternative vegetable and synthetic fibres

This paper discusses the effects of different ageing conditions on the mechanical and physical characteristics of cementitious roofing tiles reinforced with sisal and newsprint pulps, sisal strand fibre and polypropylene (PP) fibre. Roofing tiles with undulate shape were produced by a slurry de-watering and pressing technique. They were subjected to three distinct ageing conditions: fast carbonation, accelerated ageing cycles and fast carbonation plus accelerated ageing cycles. Fast carbonation did not improve the maximum load (ML), limit of proportionality (LOP), toughness and maximum deflection but did decrease their water absorption, apparent porosity and air permeability; however, after 50 heat and rain accelerated ageing cycles, it was ineffective in maintaining the mechanical properties (ML, LOP, toughness and deflection) of the tiles reinforced with vegetable fibres. The refined sisal pulp fibres led to roofing tiles with slightly higher LOP, toughness and maximum deflection than those reinforced with newsprint pulp fibres. PP fibres significantly improved the mechanical performance (ML, LOP, toughness and deflection) of the roofing tiles in relation to sisal strand fibres. The accelerated ageing cycles were effective in promoting severe degradation on the roofing tiles with sisal strand fibres, while the tiles reinforced with PP fibres were practically unaffected.

Mechanical viscoelastic behavior of dental adhesives

ObjectivesThe purpose of the study was to evaluate the mechanical properties of dental adhesive materials at different testing temperatures after dry and wet storage. MethodsSpecimens (d=1mm, l=18mm) from six materials were tested: Silorane Adhesive System (SL), Heliobond (HE), One-Step Plus (OS), Optibond Solo Plus (OP), cmf Adhesive System (CF) and Protobond (PR). Static and creep testing was performed by applying a constant torque below the proportional limit of the materials, while dynamic testing consisted of dynamic torsional loading. Experiments were performed after 24h of dry and wet storage under temperatures from 21°C to 50°C and various viscoelastic parameters were calculated. ResultsShear modulus ranged from 0.19 to 1.99GPa, while flexural modulus from 0.67 to 5.69GPa. Most of the materials were affected by the presence of water and increase of temperature. OP showed the highest recovery after creep, while SL exhibited the highest permanent deformation. SignificanceContact with water after polymerization and increase of temperature resulted in a decline of the mechanical properties, especially for the HEMA-containing adhesives.

Effect of differential swelling between fiber and matrix on the strength of irradiated SiC/SiC composites

Mechanical properties of silicon carbide (SiC)-fiber-reinforced SiC matrix (SiC/SiC) composites are sensitive to residual stresses induced during the fabrication process. Differential swelling between individual SiC fibers and the SiC matrix due to irradiation modifies the residual stresses, thereby affecting the strength of the irradiated composites. To understand the effect of irradiation on the strength of SiC/SiC composites, the swelling of the fibers and matrix was evaluated following 5.1MeV Si2+ ion irradiation corresponding to a dose of ∼3dpa at 873–1273K. The magnitude of swelling in Tyranno™-SA3 SiC fiber and a chemical-vapor-infiltrated SiC matrix was similar. The magnitude of swelling of the matrix was larger than that of the SA3 fibers by 0.2–0.5% in nano-infiltrated and transient eutectic phase (NITE) SiC/SiC composites at 873–1273K to 3dpa. This swelling mismatch can reduce the residual tensile stress in the NITE-SiC matrix and in turn improve the proportional limit stress of NITE SiC/SiC composites after neutron irradiation.

Empirical plasticity models applied for paper sheets having different anisotropy and dry solids content levels

The rheological nature of paper or board is usually treated either as elasto-plastic or as viscoelastic depending on the studied paper making process or behavior in converting and end use. In this paper we study several stress–strain curve models and the determination of material parameters from an elasto-plastic point of view. Finally, a suitable approach for all stress–strain curves measured from 180 strips is constructed using a linear function for an elastic region and a nonlinear function for a strain hardening region. This model determines a proportional limit (elastic limit) and gives fairly elegant dependencies between material/fitting parameters and two important factors of mechanical properties of paper: dry solids content and anisotropy. In this paper the dependency of a plastic strain on dry solids content and anisotropy is estimated using the introduced stress–strain curve model. Correspondingly, the model can be used to estimate many other mechanical behaviors, for example, the tension differences arising from non-uniform moisture content of the paper web profile. However, the main target of this study is to produce competent parameters based on modeled stress–strain curves for further construction of a material model. This elasto-plastic material model will be utilized in out-of-plane deformation and fracture models.

Microstructure and properties of C f /SiC composites with thin SiCN layer as fiber-protecting coating

Cf/SiC composites were prepared first by chemical vapor infiltration for formation of SiCN coating on the fiber surface, then by polymer infiltration and pyrolysis for SiC densification process. The effect of SiCN content on microstructure and mechanical properties of the composites was investigated. As the content of deposited SiCN increased, the density of the composites gradually increased. Simultaneously, the bending strength and proportional limit stress were also improved. When the preform density after SiCN deposition reached about 1.01 g/cm3, the ultimate bending strength and proportional limit stress of the final densified composites were enhanced to 386 MPa and 302 MPa, respectively. The fracture behavior of the fabricated composites was totally changed after SiCN deposition. Long fiber pullout dominated the fracture surfaces for composites with deposited SiCN, while for the one without fiber coating no fiber pullout was observed.

The Study of Hibiscus sabdariffa-reinforced-cellulose Fibre Composite

Waste biomass, in the form of Hibiscus sabdariffa stem fibre (1cm length), was used as reinforcement in a phenoplast polymer matrix to form a composite. The ratio of phenol in the phenoplast resin was varied whereas formaldehyde was kept constant; a phenol formaldehyde ratio of 0.75:1.0 and fibre:resin ratio of 12.7:87.3 were found to exhibit maximum mechanical strength. The comparative mechanical evaluation of the phenoplast and fibre-reinforced composite was performed by assessment of the hardness, modulus of rupture (MOR), modulus of elasticity (MOE), stress at the limit of proportionality (SP), tensile strength, compressive strength and wear resistance. The composites were characterized using advanced techniques. It was observed that fibre-reinforced phenol-formaldehyde (PF) composites exhibited physico-chemical resistance and improved mechanical behaviour compared with the phenoplast composite.

An Analysis of Mechanical Properties of the Developed Al/SiC-MMC’s

Metal Matrix Composites (MMC's) have evoked a keen interest in recent times for potential applications. Advance composite materials like Al/SiC metal matrix composite is gradually becoming very important materials in manufacturing industries e.g. aerospace, automotive and automobile industries due to their superior properties such as light weight, low density, high strength to weight ratio, high hardness, high temperature and thermal shock resistance, superior wear and corrosive resistance, high specific modulus, high fatigue strength etc. In this study aluminum (Al-6063)/SiC Silicon carbide reinforced particles metal-matrix composites (MMCs) are fabricated by melt-stirring technique. The MMCs bars and circular plates are prepared with varying the reinforced particles by weight fraction ranging from 5%, 10%, 15%, and 20%. The average reinforced particles size of SiC are 220 mesh, 300 mesh, 400 mesh respectively. The stirring process was carried out at 200 rev/min rotating speed by graphite impeller for 15 min. The microstructure and mechanical properties like Proportionality (MPa) limit, Tensile strength upper yield point (MPa), Tensile strength lower yield point (MPa), Ultimate tensile strength (MPa), Breaking strength(MPa), % Elongation, % Reduction in area, Hardness (HRB), Density (gm/cc), Impact Strength (N.m) are investigated on prepared specimens of MMCs. It was observed that the hardness of the composite is increased with increasing of reinforced particle weight fraction. The tensile strength and impact strength both are increased with rising of reinforced weight fraction. Different mechanical tests were conducted and presented by varying the particle size and weight fractions of SiC.

Buckling of a cantilever plate uniformly loaded in its plane with applications to surface stress and thermal loads

Buckling of elastic structures can occur for loads well within the proportionality limit of their constituent materials. Given the ubiquity of beams and plates in engineering design and application, their buckling behavior has been widely studied. However, buckling of a cantilever plate is yet to be investigated, despite the widespread use of cantilevers in modern technological developments. Here, we address this issue and theoretically study the buckling behavior of a cantilever plate that is uniformly loaded in its plane. Applications of this fundamental problem include loading due to uniform temperature and surface stress changes. This is achieved using a scaling analysis and full three-dimensional numerical solution, leading to explicit formulas for the buckling loads. Unusually, we observe buckling for both tensile and compressive loads, the physical mechanisms for which are explored. We also examine the practical implications of these findings to modern developments in ultra sensitive micro- and nano-cantilever sensors, such as those composed of silicon nitride and graphene.

Analysis of Rectangular and Circular Cross-section Power Hardening Elements Under Pure Bending

Eng ineering theory of elastic plastic bending is used in solving a grate variety of strength and durability problems. The accuracy of analysis depends on stress-strain curve idealizat ion model. The elastic linear hardening stress-strain relation is simp le and frequently used. But the actual stress-strain behaviour of ductile material in plastic reg ion is non-linear and, therefore, elastic power hardening material model is more p referab le. Moreover, the properties of monotonic tension and compression as proportional limits and parameters of hardening can differ. In this regard, analytical solution for rectangular and circular cross-section elements loading by monotonic elastic plastic pure bending is presented in the paper. The simp le power relation of stress and strain response is used. The equations describing deviation of the stress neutral axis fro m centroidal axis of an element and dimensionless bending mo ment are derived.

Influence of Niobium on the Beginning of the Plastic Flow of Material during Cold Deformation

Investigations were conducted on low-carbon steel and the steel with same chemical composition with addition of microalloying element niobium. While tensile testing was carried out, the thermographic measurement was tacking place simultaneously. A specific behavior of niobium microalloyed steel was noticed. Test results have shown that, in the elastic deformation region, thermoelastic effect occurs, which is more pronounced in niobium microalloyed steel. Start of plastic flow in steel which is not microalloyed with niobium begins later in comparison to the microalloyed steel, and it is conducted so that, at the point of maximum stress, deformation zone is formed within which stresses grow. In steel microalloyed with niobium after proportionality limit, comes the occurrence of the localized increase in temperature and the occurrence of Lüders band, which propagate along the sample forming a deformation zone.

Drop Impact Analysis of Cushioning System with an Elastic Critical Component of Cantilever Beam Type

In some electronic products and sculpture crafts, there are possibly vulnerable elements that can be idealized as cantilever beam type, failure of which will certainly lead the whole product to lose function. Based on the critical component of cantilever beam type, a nonlinear coupling dynamics model between the critical component and the item was established. The computing procedure of the model was designed using finite difference scheme. A numerical example shows that the acceleration changes notably with the length of the critical component, and the cantilevered end of the critical component is liable to be damaged, because the dynamic stress there is the largest. In this case, the maximum acceleration just cannot serve as the damaged criterion of the packaged goods, only with the maximum stress value. In order to avoid making a mistake, it is necessary to consider the critical component as an elastic element. The maximum stress of the cantilever beam surpasses the proportional limit of elastic components or is not an effective structural strength to determine whether the product loses its functions.

Assessment of certain wood quality parameters of selected genotypes of Melia dubia Cav. grown in a seedling seed orchard

Certain wood quality parameters of about 9-year-old Melia dubia Cav. trees grown in a seedling seed orchard at Yeshwanthpura Research Station of Kolar research range, Karnataka India were studied. Trees were categorized into three classes depending upon their girth at the breast height––small ( 60 cm). Different anatomical (gross structure), physical and mechanical properties of the wood were evaluated using standard testing procedures and Indian Standards. The results of this study showed that there was no significant difference in the heartwood percentage and specific gravity among three girth classes. High shrinkage values from green to oven-dry condition in all the classes indicate that the timber is dimensionally unstable compared to teak. The static bending strength parameters––FS at LP, MOR and MOE, compression strength parallel to grain, compressive strength perpendicular to grain at limit of proportionality and surface hardness (side and end) were evaluated and compared among all the three girth classes. The data on mechanical properties were statistically analysed using ANOVA between three girth classes. The results on wood quality parameters may be utilized in selection of suitable genotypes for raising large scale plantations.

Flexural properties of denture base resins subjected to long-term water immersion

Objective. The aim of this study was to investigate the flexural properties of denture base resins subjected to long-term water immersion. Materials and methods. Four denture base resins (one conventional heat-processed, one microwave energy-processed and two pour-type autopolymerizing) were selected for this study. The specimens of each denture base material tested were fabricated according to the manufacturers' instructions (n = 10). The flexural properties of the denture base resins were measured according to ISO 20795-1. The ultimate flexural strength, the flexural strength at the proportional limit and the elastic modulus of the specimens were evaluated. Results. The ultimate flexural strengths of the heat-processed resin and the two pour-type autopolymerizing resins significantly decreased after 6 months water immersion. The flexural strength at the proportional limit of the heat-processed resin significantly decreased after 6 months water immersion, but the microwave energy-processed denture base resin and two pour-type autopolymerizing resins did not change after 6 months water immersion. The elastic moduli of the heat-processed resin, the microwave energy-processed denture base resin and one pour-type autopolymerizing resin significantly increased after 6 months water immersion. Conclusion. The flexural properties of denture base resins significantly changed after long-term water immersion.

Accreditation of Novel Roselle Grafted Fiber Reinforced Bio-Composites

The reaction parameters for the graft co-polymerization of efficient Butyl acrylate (BA) monomer onto Hibiscus sabdariffa (Roselle) stem fiber were optimized and used to further explore the additive effect of methyl acrylate (MA), vinyl acetate (VA) and styrene (Sty) on percentage grafting, properties and the behavior of the fiber, in binary vinyl monomeric mixtures. The graft co-polymers were characterized by XRD, TGA, DTA, SEM and FTIR techniques and evaluated for physico-chemical changes like moisture absorption, swelling behavior, dye uptake studies and chemical resistance against 1N NaOH and 1N HCl. With increase in percentage grafting the percentage crystallinity, crystallinity index, and hydrophylicity were reduced whereas there was an increase in physico-chemico-thermal resistance, hydrophobicity, miscibility with organic solvents as a result of morphological transformation in these fibers. These modified graft copolymers were then used as reinforcement in phenol-formaldehyde polymer matrix as reinforcement and evaluated mechanically for modulus of elasticity, modulus of rupture, stress at the limit of proportionality and hardness. The composites reinforced with grafted fiber had better strength than raw fiber reinforced composites and phenoplast.

Fiber Stress at Proportional Limit

Fiber Stress at Proportional Limit

Prediction of strand feedstock mechanical properties with near infrared spectroscopy

Wood strands either prepared in the laboratory or from a manufacturing plant were assessed for their ultimate tensile strength, tensile MOE, bending strength, and bending stiffness, and then near infrared spectroscopy was utilized for prediction. The ability to predict ultimate tensile strength and stiffness was generally weaker than bending strength and stiffness, perhaps due to the homogeneous distribution of stresses that occur within the strand during 3-point bending. Prediction of ultimate tensile strength and elasticity of plant based strands were generally weak due to imperfections in the strands that originate during biomass breakdown; however, for laboratory strands, prediction of tensile strength and stiffness was moderate/better. The modulus of elasticity for strands under bending exhibited the strongest correlation (R2 = 0.76). Principal component loadings were assessed, and it was found that the cellulose crystalline- and semi-crystalline-associated wavelengths were most important in predicting the stiffness for both tensile and bending forces; however, the influence of lignin-associated wavelengths increased in importance when predicting bending strength, and it was hypothesized that this was attributable to the plastic response of lignin above the proportional limit in the stress-to-strain curve. This study demonstrates the potential of near infrared spectroscopy to monitor the biomass quality prior to composite manufacture.