Proportional Limit Research Articles

Deflection of Densified Beech and Aspen Woods as a Function of Selected Factors

Effects of selected factors (wood species (Beech, Aspen), degree of densification (10%, 20%), material thickness (4 mm, 6 mm, 10 mm, and 18 mm), and number of loading cycles (0, 10,000)) were analyzed relative to the bendability of densified wood. The monitored characteristics were the deflection at proportional limit (YE), deflection at maximum limit (YP), and their ratio (YE:YP). One of the main causes of unfavorable wood bending is its low deflection under tensile stress parallel to the fiber in comparison to compressive stress in the same direction. From the results it is clear that the deflection at the proportionality limit depended on all monitored factors. The deflection at the yield point was not influenced by cyclic loading, and the ratio of deflection was influenced by material thickness only. Based on this ratio, the moulding properties of material can be identified. There was a strong correlation between the two deflection limits. The results are an important foundation for progress in the production of laminated materials with specific properties for intended use.

Nondestructive bending tests on Douglas-fir utility poles as a potential tool for pole sorting and for prediction of their behavior in service

Abstract Wood poles are a critical part of the electrical transmission system in North America. Wood poles are normally selected on the basis of visual features such as knots, slope of grain or other defects, but there is currently no simple, nondestructive bending (NDB), pre-flexural testing for sorting poles prior to use. In the present paper, the potential for NDB based on bending below the proportional limit was examined to calculate modulus of elasticity (MOE) and thereby predict actual modulus of rupture as determined by destructive bending (MORDB). The investigation was performed on 92 full length 13.3-m long Douglas-fir pole sections. Pre-flexural testing was reasonably correlated with MOEDB, but less well correlated with MORDB. The testing also revealed that visual selection of the best face of a pole, which is used to select a pole oriented to line direction (the “best face”), was poorly correlated with pre-flexing. Increasing the number of NDB tests did not noticeably improve the prediction. The results suggest that pre-flexing might be useful for identifying poles’ performance in service, if more data are available.

Bending characteristics of hardwood lamellae in the elastic region

Abstract This article focuses on the analysis of the effect of certain factors (wood species, degree of densification, material thickness and number of loading cycles) on the modulus of elasticity (MOE), limit of proportionality (LOP) and elastic potential (PE) of beech and aspen wood lamellae measured in the elastic region of the stress-strain curve under bending loading. Beech wood achieved higher MOE, LOP and PE values than aspen wood. As the degree of densification increased, the MOE and LOP also increased, while the PE remains almost unchanged. MOE values increase as the material thickness increases, while the LOP and PE decrease. Cyclic loading caused an increase in the LOP and PE, but it had little effect on the MOE. Cyclic loading had a greater effect on densified wood than non-densified wood.

Identifying the Characteristics of Laminated Wood Based on the Values of Deflection Measured during its Bending

This article is aimed at verifying the influence of selected factors (wood species, lamella combination, type of adhesive, number of loading cycles) on the deflection at the proportionality limit YE, deflection at the point of rupture YMOR, and the ratio between the deflection at the proportionality limit and the deflection at the point of rupture YE :YMOR. All of the monitored characteristics were evaluated on test specimens made from lamellas of beechwood (Fagus sylvatica L.) and aspen wood (Populus tremula L.). The laminated wood consisted of a combination of lamellas that were non-densified and densified to 10% and 20% of their original thickness. Two types of adhesives were used for the research: polyvinyl acetate (PVA) glue and polyurethane (PUR) glue. The results create a database of information that can be used in developing materials with specified properties for its intended use.

Influence of concrete strength combined with fiber content in the residual flexural strengths of fiber reinforced concrete

Recently, the design and construction of fiber reinforced concrete structures, such as floor slabs and precast tunnel linings, require using the actual values of the residual flexural strength instead of the average concept of the equivalent residual flexural strength ratio. An experimental study was performed to examine the direct residual flexural strengths of steel fiber reinforced concrete beams with various concrete strengths, 25, 35, and 45MPa, and fiber volume factions, 0.25, 0.375, and 0.50%. The influence of the concrete strength and fiber content in the limit of proportionality, residual flexural strength, and energy absorption capacity were evaluated. The fiber reinforced concrete beams with a strength of 45MPa showed a higher increase in the residual flexural strength immediately after concrete cracking, particularly for a fiber volume fraction of 0.5%. On the other hand, as concrete cracking propagated, the residual flexural strength and energy absorption capacity values rapidly decreased in the beams with a concrete strength of 45MPa.

Investigation on Concrete Reinforced with Two Types of Hooked Fibers under Flexure

Steel fiber reinforced concrete (SFRC) is a material widely used for structural applications. The effectiveness of the steel fibers in the concrete matrix is strongly affected by the shape of the fibers. Because the steel fibers with various geometrical parameters are currently available, the knowledge about their influence on concrete response is needed. The paper presents the investigation on concrete reinforced with new type of fibers which are crimped along the length with additional hooks at the ends. To estimate the effect of this kind of fibers on the mechanical parameters of SFRC the typical hooked fibers were also investigated. The compressive and three-point flexural tensile tests were performed on specimens where three fiber contents were applied: 0.32%, 0.45% and 0.57%. The results indicate that the fracture energy did not differ apparently, whereas in the equivalent tensile strengths some differences were noted due to the change of fiber shape. The difference was only observed in the shape of the load-deflection curves obtained from the tests with a use of two fiber types. However, the compressive strength and flexural tensile strength at the limit of proportionality were more affected by crimped and hooked fibers than typical hooked ones. It shows that the new type of fiber may delay the formation of the cracks in the SFRC.

The shear behaviour of pine wood in the Arcan test with the digital image correlation

The Arcan shear test is used together with the digital image correlation to study the shear stress-strain relationship for pine wood in the symmetry plane LR . The relationship of shearing perpendicular to the grain direction is shown by the straight line below the proportional limit and the nonlinear curve beyond it describing hardening up to the ultimate limit. Subsequent failure modes are shown during the load increase. Additionally, some results of the off-axis tension tests, as well as the uniaxial tension tests, with the mechanical and electric resistance strain gauges are presented to determine and compare the shear modulus from both methods of testing.

Elastic constants of green Pinus radiata wood

Mathematical modelling is often used to investigate phenomena difficult or impossible to measure experimentally. This paper presents the constants needed to mathematically model green Pinus radiata D.Don core- and outerwood. The constants include all three elastic and shear moduli along with the six Poisson ratios needed for describing orthotropic materials in the elastic domain. Further proportional limit surfaces are presented. The constants provided allow for an increase in realism of mathematical models examining the mechanical performance of standing trees.

Mud House Failures and Mitigation Options in Bauchi, North East Nigeria

The use of soil materials for sustainable construction in developing countries is a viable alternative to concrete based materials. The advantages include availability of soil (earth) materials, reduction of transportation cost, saved embodied energy, reduced environmental degradation and reduced material cost. Mud house collapse is a common yearly phenomenon in Nigeria. Much of this happens during rainy seasons due to flooding generated by heavy rainfall. Whenever this happened, people were rendered homeless and became Internally Displaced Persons (IDP), with the subsequent hardships and sufferings, and sometimes casualties. Sixty seven mud houses in three locations of Bauchi town, North East of Nigeria were investigated. From observations and returns from structured questionnaires filled by house owners and tenants, about 76% of the houses had failed in form of wall collapses alone. Other data collected included age of houses, composition of wall materials and foundations. Failures were generally severe and widespread for walls of full mud houses, however those plastered with cement/sand mortar had less failure counts. Older mud houses recorded higher failures as against new constructions. Soil samples collected from borrow pits used for the investigated mud houses were tested and their soil type compositions determined in the laboratory. They slightly fell short of the specified proportional limits of clay, silt and sand considered acceptable for construction purposes except stabilized. Sample bricks made from the soils were tested for compressive strength with an average value of 0.81N/mm2 which is far below the 2.5N/mm2 minimum value for sandcrete blocks specified by the Nigerian Standards Organization. Lack of good quality control measures and improper stabilization procedures, among others were considered responsible for the failed resistance to the environmental factors. Cement stabilization and good urban planning are some of the recommendations.

Limit Dependences in Stability Calculations With Account for Physical Nonlinearity

AbstractStability of bars, plates, shells, and other thin-walled structures in conditions of small physical nonlinearity is considered, when stresses exceed the proportionality limit, the amount of deformations being limited. Shanley's concept is used. The critical state is determined by means of some limit dependences. In a large number of cases, when creating efficient highly-stressed constructions, limited plastic deformations are allowed in them. When analysing stability in the critical state, the calculated stresses turn out to exceed the proportionality limit and the Young's modulus of elasticity turns out to be greater than the tangent modulus corresponding to the calculated stress on the diagram “deformation-stress”. The objective of this work is to show that stability calculation beyond the proportionality limit is reduced to the analysis of some limit dependences as well as to develop a general solution algorithm for similar problems.

Experimental investigation of the mechanical behavior of the steel fiber reinforced concrete tunnel segment

The main objective of this paper is to investigate the composite effect of steel fiber and steel rebar on the mechanical behavior of full-scale steel fiber reinforced concrete (SFRC) precast tunnel segments fabricated for a subway tunnel in China. A new biaxial loading method was adopted to simulate the loading state of the tunnel segment. The experiment included an initial SFRC tunnel segment proposed for the project, and two other SFRC tunnel segments were employed for comparison. By comparing the test results, the static characteristics of the three segments, including the internal strain, deflection, neutral axis position and crack patterns were determined. The experimental results indicate that the combined used of steel fiber and steel rebar shows an enhanced effect by delaying the initial impact of cracking and increasing the limit of proportionality of the segments. Longitudinal rebar in the tensile region were more helpful in decreasing tension strain and deflection in the mid-span section than the steel fibers. However, steel fibers performed better in improving the cracking load, cracking resistance and toughness. Furthermore, the initial SFRC tunnel segment proposed for the project exhibited a significant reduction in crack width and satisfied the design criteria for load carrying ability and crack width. The combination of steel fiber and steel rebar indicates an optimal choice of reinforcement for a tunnel segment.

Tablas de clasificación de algunas propiedades mecánicas de maderas mexicanas en condición “verde”

No existen tablas para clasificar algunas de las propiedades mecánicas de interés para los usuarios de la madera: trabajo al límite de proporcionalidad en flexión, módulo de elasticidad en compresión paralela a la fibra y esfuerzo a 1 mm de deformación en compresión perpendicular a la fibra. En este trabajo se propone una clasificación para madera “verde” basada en datos de pruebas efectuadas a lo largo de varios años, registrados en el Departamento de Productos Forestales y Conservación de Bosques del Instituto de Ecología, A.C. Esta tabla complementa otras presentadas anteriormente por investigadores de esta institución.

Causal exclusion and the limits of proportionality

Causal exclusion arguments are taken to threaten the autonomy of the special sciences, and the causal efficacy of mental properties. A recent line of response to these arguments has appealed to “independently plausible” and “well grounded” theories of causation to rebut key premises. In this paper I consider two papers which proceed in this vein and show that they share a common feature: they both require causes to be proportional (in Yablo’s sense) to their effects. I argue that this feature is a bug, and one that generalises: any attempt to rescue the autonomy of the special sciences, or the efficacy of the mental, from exclusion worries had better not look to proportionality for help.

Características anatómicas y propiedades mecánicas de la madera de Oecopetalum mexicanum Greenm. & C.H. Thomps. (Icacinaceae) de la sierra de Misantla, Veracruz, México

Se describe por primera vez la anatomía de la madera de Oecopetalum mexicanum ( cachichín ) Greenm. & C.H. Thomps., la cual es una especie que crece en los bosques y ecosistemas de café de la sierra de Misantla, Veracruz, México. Con el fin de conocer sus posibles usos, se determinaron las propiedades mecánicas en flexión, del tipo: esfuerzo en el límite de proporcionalidad, trabajo unitario en el límite de proporcionalidad, módulo de elasticidad, módulo de ruptura y trabajo unitario a carga máxima; en compresión paralela a la fibra, como lo fue el esfuerzo máximo, esfuerzo en el límite de proporcionalidad y módulo de elasticidad. Todo ello, en su madera en condición verde. Se investigó también la densidad relativa básica de cada muestra, así como el diámetro, la distribución y densidad de los vasos, la abundancia y distribución del parénquima axial y radial. A partir de macerados, se identificó el tamaño de los elementos de vaso, tamaño de las fibras y contenidos celulares. La descripción anatómica se basó en la IAWA List of microscopic features for hardwood Identification (IAWA 1989) . Los resultados obtenidos a la fecha indican que la madera del cachichín tiene resistencia similar a la del pino y, en algunas propiedades, incluso lo supera. Por lo tanto, es apta para la construcción, siempre y cuando se utilice todo el tronco y solo cuando sea posible aserrarla, se usarán piezas prismáticas aserradas.

The Moral Limits of Proportionality in War

Given the limit on civilian casualties imposed by the rule of proportionality, some observers have asked whether the “good guys” can win with the current law and morality of war in place. Contrary to the lawyers, philosophers, and military practitioners who have sought to liberalize the standard of acceptable civilian casualties in war, this paper argues that the most promising attempts to morally justify more harm to civilians than harm averted ultimately fail. The paper focuses on two central arguments for a more liberal proportionality standard: (i) that defending forces who put civilians in harm’s way relieve the moral responsibility of attacking forces for civilian deaths, and (ii) that associative duties justify more killing of enemy civilians to save our compatriots. The first argument fails because it erroneously assumes that a party’s moral responsibility is diminished when more than one party is causally responsible for the same wrong. While liability may be diminished for civil harms when accidents occur, morality, like criminal law, does not recognize diminished responsibility when fundamental moral obligations are at stake. The second argument also rests on dubious assumptions. The special obligations that arise from associative relations cannot trump our general obligations not to harm others or establish claim rights that are wronged when we fail to privilege the lives of our associates over the lives of others. Our special obligations are generally limited precisely at the point where they would begin to do direct harm to nonthreatening others. Whether we are considering conventional war, counterterrorism, or human shields, proportionality’s excessiveness standard represents the maximal approach to justifiable civilian deaths in armed conflict.

LOCAL WISDOM IN UTILIZING PEAT SWAMP SOIL AND WATER TO IMPROVE QUALITY OF GELAM WOOD

Local wisdom in utilizing swamp soil and water to improve the quality of gelam wood in Central Kalimantan becomes an interesting phenomenon. Improving the quality of wood can economize on the use of wood, which in turn preserves the forests in peat swamp lands. Gelam (Melaleuca sp.) woods that are mostly found in peat swamp forests can be used as piles/stakes in swamp soil, and they are durable for decades. The general objective of this study was to provide a scientific explanation of the effect of peat swamp soil and water on improving the quality of gelam wood either in barked and barkless conditions. This study was conducted by taking gelam trees that grew in Central Kalimantan. It was carried out for 18 months, and investigated the barked/barkless woods, media (swamp water, freshwater, peat swamp soil, and sandy soil) and 3 lengths of burying times. Wood properties analyzed were physical and mechanical properties. The standard of physical-mechanical property tests referred to British Standard 373. The results showed that the interaction between bark factor (A) and media (B) affected specific gravity. Barked wood produced the highest spesific gravity in swamp water medium. Water media (swamp and fresh water) improved the wood’s specific gravity more than soil media (swamp and sandy soil). The highest values of hardness, stress on Proportional Limit, and Modulus of Elasticity were in the medium of swamp soil. The improvement of the quality of gelam woods, which were either buried or used as stakes/piles, was allegedly resulted from the swamp water infiltrating into gelam woods that thereby increased the specific gravity.

Uncoupled thermoelasticity solutions applied on beam dumps

In particle accelerators the process of beam absorption is vital. At CERN particle beams are accelerated at energies of the order of TeV. In the event of a system failure or following collisions, the beam needs to be safely absorbed by dedicated protecting blocks. The thermal shock caused by the rapid energy deposition within the absorbing block causes thermal stresses that may rise above critical levels. The present paper provides a convenient expression of such stresses under hypotheses described hereafter. The temperature field caused by the beam energy deposition is assumed to be Gaussian. Such a field models a non-diffusive heat deposition. These effects are described as thermoelastic as long as the stresses remain below the proportional limit and can be analytically modeled by the coupled equations of thermoelasticity. The analytical solution to the uncoupled thermoelastic problem in an infinite domain is presented herein and matched with a finite unit radius sphere. The assumption of zero diffusion as well as the validity of the match with a finite geometry is quantified such that the obtained solutions can be rigorously applied to real problems. Furthermore, truncated series solutions, which are not novel, are used for comparison purposes. All quantities are nondimensional and the problem reduces to a dependence of five dimensionless parameters. The equations of elasticity are presented in the potential formulation where the shear potential is assumed to be nil due to the source being a gradient and the absence of boundaries. Nevertheless equivalent three-dimensional stresses are computed using the compressive potential and optimized using standard analytical optimization methods. An alternative algorithm for finding the critical points of the three-dimensional stress function is presented. Finally, a case study concerning the proton synchrotron booster dump is presented where the aforementioned analytical solutions are used and the preceding assumptions verified.

Effect of PCL and Compatibility Contents on the Morphology, Crystallization and Mechanical Properties of PLA/PCL Blends

This study focused on the effect of PCL on crystalline morphology, isothermally crystallization of PLA in PLA/PCL blends using POM on investigation. The blend with Pluronic used as a plasticizer was also studied. The blends were prepared by melt blending in an internal mixer. The contents of PCL incorporated were varied from 0-30% by weight. The content of Pluronic used in this study was at 2.5, 5 and 7.5 phr. The blends were characterized for their morphology, crystallization and mechanical properties. Melt strength of the blends was also investigated. The morphology of the blends confirmed immiscibility of two polymer phases. Scanning electron microscope (SEM) of PLA/PCL blends indicated larger particle size of PCL dispersed in PLA with the increase of PCL contents. Tg of PLA in the blend could not be observed on Differential Scanning Calorimetry (DSC) traces. This was due to the overlapping with Tm of PCL. The presence of Pluronic in PLA/PCL blends resulted in Tms shifting to slightly lower temperatures. The crystallinity of PLA was also decreased. The spherulitic growth of PLA in blends was followed by polarized optical microscope using isothermal condition at 141°C. The spherulite structure was found affected by the presence of Pluronic hence effect on crystallization of PLA. Tensile properties of PLA/PCL blend were suffered with PCL content except for elongation at break which seems to be enhanced. It was found that the presence of pluronic in PLA/PCL blend increased ductility of the blends. At Plurunic of 2.5 phr and PCL content of 10-20% by weight, tensile strength of these blends was increased. This was explained by the fine dispersed PCL particles facilitated orientation of PLA chain after proportional limit and hence increased tensile strength. With higher content both PCL and Pluronic, large PCL particle size was disadvantaged for tensile properties.

The elastic–plastic transition of metals

Uniaxial stress–strain curves are known to exhibit significant curvature and hysteresis even in the nominally elastic regime, i.e. before the standard yield stress is attained. In order to probe the nature of this behavior, hundreds of high-precision loading–unloading–loading tensile tests were performed using 26 commercial sheet alloys exhibiting a wide range of strength, ductility and crystal structure. Corresponding analysis shows that:1There is no significant linear elastic region, that is, the proportional limit is 0 MPa. While the first increment of deformation shows a stress–strain slope equal to Young's modulus, progressive deviations of slope start immediately.2The shape of the transitional stress–strain curve can be represented by a simple one-parameter equation representing the “modulus reduction rate.” It captures ∼80% of the measured variation and can be determined from a single test. This approach reduces the error inherent in standard Young's modulus or chord modulus approximations by a factor of 3–6.3A “Universal Law” having no independently-determined parameters, i.e. no testing or fitting required, was developed. It captures ∼90% of the variation represented by the one-parameter representation for the materials tested.The practical and theoretical implications of these results are discussed. On the practical side, the results provide an immediate path to improving applied constitutive models in the transitional regime. An example of an application and results is provided. On the theoretical side, the consistency of the effect for a wide range of metals suggests answers to questions about the governing deformation mechanisms.

The effect on the tensile properties of PIP-processed SiC/SiC composite of a chemical vapor-infiltrated SiC layer overlaid on the pyrocarbon interface layer

A chemical vapor-infiltrated (CVI) SiC layer is often deposited on the pyrocarbon (PyC) fiber–matrix interface layer in SiC fiber-reinforced SiC matrix (SiC/SiC) composites. It is normally applied to protect the PyC layer from reacting with molten Si or sintering aids during manufacturing, and to guard against the effects of high temperature, oxidation and moisture during use. In this study, we investigated the effect of this SiC layer on the tensile properties of a composite. Tensile tests of our composite samples showed the SiC layer to have no noticeable effects on its ultimate load or fracture strain, whereas it decreased the load-to-strain ratio and proportional limit. The test results were analyzed by carrying out element tests on filaments and fiber bundle samples, fracture mirror analysis of pullout fibers, and finite element analysis (FEA) of residual thermal stress around the interface.