Rate Of Load Application Research Articles

An improved creep correction factor for footings on sand using macro-element simulations

In many settlement prediction methods, the creep settlement of shallow foundations on sand is either disregarded or accounted for using time correction factors that lack a reliable basis. These existing settlement correction factors for creep have mainly been derived from a restricted number of long-term settlement measurements and do not consider the influence of factors such as the load level, rate of load application and properties of the soil below the foundation. In this study, a newly proposed one-dimensional elasto-viscoplastic macro-element was used to investigate the factors influencing the time-dependent behaviour of shallow foundations on sand. The safety factor of the foundation, the creep characteristics of the soils and the duration of load application were found to have important effects on the post-construction settlement development. The simulation results were used to develop an enhanced settlement correction factor for creep, which takes into account the identified factors. The improved settlement correction factor was found to be comparable to existing ones when the safety factor of the foundation is 3. The effectiveness of the proposed settlement correction factor is demonstrated using creep settlement measurements from one field footing test and two case histories.

Study of the strength limit of the bark of a plum tree trunk under the action of normal compression

Purpose. Reduction of damage to trunks of tree bark due to substantiation of the parameters of the harvesting technique using the method of determining the strength limit of tree bark in field conditions during research and the device for its implementation. Methods. Standardized and improved methods of determining the strength limit of tree bark under normal load were used, as well as the basic provisions for conducting laboratory and field experiments. Results. During field research, the developed method of determining the strength limit of tree bark was applied. It was established that highly elastic deformation of the bark does not affect the functional properties of phloem, phelloderm and cambium, i.e. after removing the load, the bark is completely restored, and irreversible plastic deformation leads to the death of bark fibers. The transition to the region of plastic deformation is marked by a sharp increase in the rate of deformation at a constant rate of load application, i.e. the strength limit of the crust is overcome and the flow fluidity phase. To implement the improved method, the developed device was used to determine the strength limit of the crust under normal compression, which made it possible to substantiate the parameters of the overlays of working organs and modes of operation of shakers of fruit-harvesting means and machines during development. Conclusions. The proposed method and device made it possible to determine the bark strength limit during normal compression in the field without damaging the tree bark. It was established that for plum orchard trees with diameters of 50–200 mm, it is 0.68–1.74 MPa and depends on the thickness of the cork tissue, which increases with the age of the tree. The method of implementing the method and the device is universal, therefore it is advisable to use it during field tests to determine the limit of bark strength for other fruit and nut trees. Keywords: method, instrument, tree bark, normal pressure, strength limit.

Distal radius fracture fixation using volar plate: A comparative study evaluating the biomechanical behavior of uni and bicortical distal screws

Extensor tendon ruptures caused by bicortical screws impingement following distal radius fracture fixation with volar plates are extensively reported in the literature. Thus, a biomechanical study comparing unicortical and bicortical fixations in intra-articular distal radius fracture models is critical in decision-making regarding distal radius fracture management. Forty-two synthetic radius models were fixed using a variable angle volar distal locking plate with seven screws. They were divided into 6 groups (n = 7): G1/G3/G4 unicortical fixation (75% of anteroposterior distal radius lenght); G2/G4/G6 bicortical fixation. Each group underwent a different mechanical test: axial compression (G1/G2), dorsal flexion (G3/G4), and volar flexion (G5/G6). The load application rate was 5 mm/min and 1000 cycles of 50 to 250 N at 1 Hz were performed between both static tests. Comparative results in the first static test, in the second static test, and in failure generally showed a very similar behavior. Models depicted similar behavior in the second static test when cyclic load was performed. Therefore, one can realize that stiffness differed during dorsal flexion only in the first static test. Maximum force to break the model in axial compression was greater in bicortical than in unicortical construct. Since biomechanical properties are similar, we recommend using unicortical distal locking screws in distal radius fracture fixation with volar plates to prevent extensor tendon ruptures.

The effect of stabilizing additives on deformation performance of stone matrix asphalt

The goal of the research is to establish the effect of stabilizing additives on a number of deformation and strength indicators responsible for ensuring the durability of stone matrix asphalt (SMA), which are the complex modulus of elasticity, shear stability and bending tension. The modulus of elasticity value measurement was made on KhNAHU’s vibration table using electrodynamic transducer in the temperature range from -20 °C to +50 °C. In the deformation frequency range from 0.01 Hz to 50 Hz, shear stability was estimated by the value of shear limit strength at the temperature of 50 °C on special cylinder samples in conditions of their torsion (simple shear). The bending tension value was estimated on beam sample at different load application rate at the design temperatures of 20 °C, 10 °C and 0 °C. According to temperature dependences of modulus of elasticity, the estimate of SMA physical parameters, such as conditional mechanical glass transition temperature, viscoplastic transition temperature, temperature sensitivity of material and plasticity coefficient, was obtained. The values of shear limit strength with different stabilizing additives (VIATOP, DOLONIT) were obtained. A correlation between shear stability and compressive strength at the temperature of 50 °C was established. Comparison of deformation properties of SMA with asphalt concrete and polymer asphalt concrete using the same consistency of binder was made. The effectiveness of SMA hardening by different stabilizing additives on the basis of temperature dependences of bending strength was determined. The plastic range and temperature sensitivity values of SMA are similar to those of asphalt concrete and polymer asphalt concrete. These parameters are mainly determined by the properties of binder, such as penetration, softening temperature, etc. Polymer asphalt concrete has the highest value of plastic range and the lowest one of temperature sensitivity. The similar patterns are obtained for shear stability. The choice of stabilizing additives affects the deformation-strength properties of SMA. To improve durability of SMA, it is necessary to use polymer modified bitumen

Rheological properties of modified asphalt binder with nanosilica and SBS

Rheology is the science that deals with the deformation of materials relation with load and time rate of load application. The goal of this study is finding effects of two modifier nanosilica (nSIO2) and Styrene Butadiene Styrene (SBS) on the chemical bonding and rheological properties of local asphalt binder. In this study, 3% and 5% of nanosilica (nSIO2) and Styrene Butadiene Styrene (SBS) were added to the asphalt binder. It was found that with the addition of nanosilica to the control asphalt binder lead to slightly increased the viscosity of the control binder, as SBS polymer add the viscosity increased three times than reference viscosity of control asphalt binder. It was noticed the performance grade (PG) of binder not changed with addition of 3% nSIO2, but PG increased one degree when 5% of SIO2 is added. PG of control binder increased two and three degrees with additional 3% and 5% SBS respectively. The results show that nSIO2, and SBS slightly effect on the low temperature performance, therefore, low temperature grade not changed. Through FTIR results, it was found that the modified asphalt binder had a positive effect on anti-oxidation as compared with control binder, so, rutting and fatigue cracking performance of modified asphalt binders will be enhanced.

Dynamic Properties of Geologic Specimens Subjected to Split-Hopkinson Pressure Bar Compression Testing at the University of Kentucky

Advances in materials science have shown that material behavior varies according to the rate of load application (strain-rate sensitivity). With regards to compressive strength, materials have been observed to exhibit a strengthening, weakening, or negligible response to increasing strain-rates (Zhang and Zhao in Rock Mech Rock Eng 47(4):1411–1478, 2014). Practical experimentation to ascertain these responses has been carried out for over a century, based on the fundamental equipment design pioneered by John Hopkinson in 1872 and modified by Kolsky in 1949. A contemporary Split-Hopkinson Pressure Bar (SHPB) has been constructed at the University of Kentucky (UKY) to research the dynamic properties of various geologic materials for mining and civil engineering applications. Geologic samples are of an inconsistent nature due to inherent discontinuities and large grain size. To ensure test specimens are of adequate size to reflect this inconsistent nature, the SHPB at the UKY has been constructed with component bars of 2 in. (5.08 cm) diameter. Prior publications have discussed various considerations associated with the testing procedure and data processing of this SHPB (dispersion correction, pulse shaping, etc.) (Silva and Lamont 2017). This publication presents the results of materials testing with this SHPB. Three materials were selected: Bedford (Indiana) Limestone, Berea (Ohio) Sandstone, and Aluminum 6061-T6. Two of these are common aggregates found in the mining and construction industries, while the third is an aluminum variant often encountered in industrial applications. Dynamic compression testing of these materials at various strain rates was carried out, and the results are included. Static test results have been included for comparison, and the testing and data analysis procedure are discussed in detail.

Corrosion fatigue testing: the combined effect of stress and high temperature corrosion

A corrosive environment can have a detrimental effect on the fatigue life of a material due to a change in failure mechanism. Attempts have been made to replicate this change on nickel-base superalloy CMSX-4 cast in the <001> orientation. Fatigue testing in air, of this material typically produces a fracture on an angle of approximately 55° which is consistent with the fracture having propagated on a {111} slip plane. The aim of the research was to fatigue test in a corrosive environment with the purpose of producing a crack/fracture which deviated from the typical angle and thus confirm that the corrosive environment had affected the fatigue mechanism. It was concluded that the change in mechanism to high temperature corrosion fatigue was associated with a reduced load application rate together with precorroding the test specimens to trigger the initiation of the corrosion fatigue mechanism.

RHEOLOGICAL PROPERTIES OF STYRENE BUTADIENE RUBBER MODIFIED BITUMEN BINDER

The study investigates the rheological properties of bitumen of 60-70 penetration grade modified with Styrene Butadiene Rubber (SBR). SBR is an elastomer which is an important sort of synthetic rubber. It is a copolymer whose molecular structure primarily consists of organic compound styrene and butadiene chain. Bitumen is visco-elastic in nature. The rate of load application and temperature has a great influence on its performance. Various fundamental properties of bitumen were evaluated, namely complex shear modulus (G*), short-term ageing, long-term ageing, viscosity, penetration and softening point by using Dynamic Shear Rheometer (DSR), Rolling Thin Film Oven Test (RTFOT), Pressure Aging Vessel (PAV), Rotational Viscometer (RV), Penetrometer and Ring and Ball Test, respectively. The binders were mixed with varying percentage of SBR i.e. 0, 1, 2, 3, 4, and 5% by the weight of bitumen binder. The use of SBR has played an active role in improving the viscoelastic properties of bitumen. The use of SBR modifier changes the rheological behavior of bitumen by increasing its complex shear modulus (G*) and the resistance of mixture against permanent deformation (rutting). It was also found that increasing the content of SBR led to the increase in viscosity of modified bitumen, which helps in elevating the mixing and compaction temperature of asphalt mixtures.

New insights on free energies and Saint-Venant’s principle in viscoelasticity

Explicit expressions for the minimum free energy of a linear viscoelastic material and Noll’s definition of state are used here to explore spatial energy decay estimates for viscoelastic bodies, in the full dynamical case and in the quasi-static approximation.In the inertial case, Chirita et al. obtained a certain spatial decay inequality for a space–time integral over a portion of the body and over a finite time interval of the total mechanical energy. This involves the work done on histories, which is not a function of state in general. Here it is shown that for free energies which are functions of state and obey a certain reasonable property, the spatial decay of the corresponding space–time integral is stronger than the one involving the work done on the past history. It turns out that the bound obtained is optimal for the minimal free energy.Two cases are discussed for the quasi-static approximation. The first case deals with general states, so that general histories belonging to the equivalence class of any given state can be considered. The continuity of the stress functional with respect to the norm based on the minimal free energy is proved, and the energy measure based on the minimal free energy turns out to obey the decay inequality derived Chirita et al. for the quasi-static case.The second case explores a crucial point for viscoelastic materials, namely that the response is influenced by the rate of application of loads. Quite surprisingly, the analysis of this phenomenon in the context of Saint-Venant principles has never been carried out explicitly before, even in the linear case. This effect is explored by considering states, the related histories of which are sinusoidal. The spatial decay parameter is shown to be frequency-dependent, i.e. it depends on the rate of load application, and it is proved that of those considered, the most conservative estimate of the frequency-dependent decay is associated with the minimal free energy. A comparison is made of the results for sinusoidal histories at low frequencies and general histories.

Effect of load application rate and temperature on the fracture energy of asphalt mixtures. Fénix and semi-circular bending tests

Significant progress to address the effect of load application time and temperature on the fracture energy of asphalt mixtures was made in a comprehensive research effort as part of two national pooled-fund studies addressing low-temperature cracking in the US. Two fracture methods were thoroughly investigated and were proposed for standardization: the Disc-Shaped Compact Tension DC(T) test and the Semi Circular Bending (SCB) test. Recently, a simpler test that combines the advantages of both DC(T) and SCB configurations has been developed and successfully used in Spain, the Fénix test. This paper presents the results from the application of SCB and Fénix tests in the assessment of fracture behavior of different types of mixtures and the effect of both loading rate and temperature on the results obtained. The main conclusion is that both SCB and Fénix tests give similar information when comparing two types of mixtures or selecting mixtures resistant tocracking.

The effects of water content, temperature and loading rate on strength and failure process of frozen rocks

The effects of water content, temperature and loading rate on the strength and failure process of rock at sub-zero temperatures were investigated and are presented in this paper. Over the range of temperatures studied there was little change observed in the properties of dry rock. The presence of water in the rock, however, resulted in a marked increase in rock strength and the fracture initiation stress. Rock strength increased with amount of water present and the rate of load application, with the effect being exacerbated at the colder temperatures. Interestingly, the changes in strength were not uniform as there was a greater rate of increase in the tensile strength of rock with temperature than compressive strength. It is postulated that these changes in mechanical properties may be explained in part by a reduction in the stress concentration within the interstitial spaces and cracks of the rock samples tested.

Influence of the load application rate and the statistical model for brittle failure on the bending strength of extruded ceramic tiles

In this paper we investigate the influence of the load application rate (V) on the calculation of the bending strength (σB) of extruded ceramic tiles using three-points bending test as stated by ISO 10545. We also evaluate the convenience of using the average strength as the representative strength of a ceramic lot, and the goodness of the Gaussian distribution in comparison with the Weibull one to predict the behavior of the extruded ceramic material. Results show that there is a minimal influence of V on σB, although elevated velocities lead to higher results scattering. Hence, medium velocities are recommended to decrease time required for quality control during serial production. On the other hand, Gaussian and Weibull distributions differ in the prediction of the ceramic material to fracture, thus the selection of one probabilistic model should be in accordance with the design and working requirements of the each product under development.

CONCENTRAÇÃO DE MACRONUTRIENTES E DE SÓDIO NA PARTE AÉREA DE ESPÉCIES VEGETAIS, CULTIVADAS DE FORMA CONSORCIADA E EM DIFERENTES POSIÇÕES EM SISTEMAS ALAGADOS CONSTRUÍDOS

Neste trabalho, teve-se, como objetivo, avaliar a concentração de macronutrientes e de sódio na parte aérea de diferentes espécies vegetais, quando cultivadas na forma consorciada, em sistemas alagados construídos (SACs), utilizados no tratamento de esgoto doméstico. Para isso, foram construídos quatro SACs de fluxo subsuperficial horizontal, com 0,35 m de altura, por 1,0 m de largura e 24,0 m de comprimento, impermeabilizados com geomembrana de policloreto de vinila (PVC), preenchidos com 0,30 m de brita zero e cultivados com três espécies vegetais (taboa, capim tifton 85 e alternantera), em quatro posições distintas. A taxa de carga orgânica e a vazão, aplicadas diariamente aos SACs, foram de 200 kg ha-1 d-1 e 1,6 m3 d-1, respectivamente, de modo a proporcionar tempo de detenção hidráulica de 1,8 dia. De acordo com os resultados, pode- se afirmar que apenas a concentração de fósforo na parte aérea das plantas foi influenciada pela posição de cultivo das plantas nos SACs; dentre todas as espécies avaliadas, a alternantera apresentou as maiores concentrações de macronutrientes, com exceção do potássio e do sódio, independentemente de sua posição de cultivo nos SACs; o capim tifton-85 não deve ser cultivado no primeiro terço dos SACs, tendo em vista que não resiste às condições do meio.

The effect of load application rate on the biomechanics of synthetic femurs

Biomechanical investigations are increasingly using commercially available synthetic femurs as surrogates for human cadaveric femurs. However, the rate of force application in testing these artificial femurs appears to be chosen arbitrarily without much consideration to their visco-elastic time-dependent nature. The aim of this study, therefore, was to examine the effect of loading rate on the mechanical behaviour of synthetic femurs. Ten left, medium, fourth-generation composite femurs (Model 3403, Pacific Research Laboratories, Vashon, WA, USA) were fixed distally into cement-filled steel cubic chambers for mounting into a mechanical tester. In randomized order, each of the ten femurs was loaded at rates of 1, 2.5, 5, 7.5, 10, 20, 30, 40, 50, and 60 mm/min to obtain axial, lateral, and torsional stiffness. Axial stiffness showed an aggregate average value of 1742.7 +/- 174.7 N/mm with a high linear correlation with loading rate (R2 = 0.80). Lateral stiffness yielded an aggregate average value of 56.9 +/- 10.2 N/mm and was linearly correlated with loading rate (R2 = 0.85). Torsional stiffness demonstrated an aggregate average value of 176.9 +/- 14.5 N/mm with a strong linear correlation with loading rate (R2 = 0.59). Despite the high correlations between stiffness and speed, practically this resulted in an overall average difference between the lowest and highest stiffness of only 4 per cent. Moreover, no statistical comparisons between loading rates for axial, lateral, or torsional test modes showed differences (p > or = 0.843). Future biomechanical investigators utilizing these synthetic femurs need not be concerned with loading rate effects over the range tested presently. This is the first study in the literature to perform such an assessment.

Compressive and shear resistance of materials under dynamic rates of load application

The dynamics of formation of stresses and strains and of strain rates due to compressive and shear deformation of about 103 sec−1 in impact tests performed with the use of a Hopkinson split bar is considered. At an impact speed of up to 400 m/sec the stresses and the strain rate before failure are shown to oscillate at a high frequency (40–100 Hz). It is shown that the fracture resistance of aluminum alloys AMg6 and V95, of steel KhVG, and of ceramics from silicon carbide and alumina differs substantially under static and dynamic loads; the difference also depends on the kind of stress state.

Análise comparativa das propriedades mecânicas do ligamento da patela e do tendão calcâneo

Com a finalidade de se comparar as propriedades mecânicas do ligamento da patela e do tendão calcâneo foram realizados ensaios de tração em material obtido de 25 cadáveres humanos. A idade dos doadores foi 58 ± 14 anos (33-85), sendo 19 (76%) masculinos e 6 (24%) femininos, 23 brancos (92%) e dois negros (8%). Os materiais foram testados em seus 10 mm centrais, com velocidade de aplicação de carga de 30 mm/min. Foi obtida a área de secção dos corpos de prova para que fossem estudadas as propriedades estruturais e materiais. Foram estudadas as seguintes variáveis: carga máxima (N), tensão(MPa), módulo de elasticidade (MPa), energia (Nm), alongamento absoluto (mm) e específico (%), limite de proporcionalidade (N), além da tensão (MPa) e alongamentos neste ponto. A análise estatística revelou que ambos possuem carga máxima, limite de proporcionalidade e tensão semelhantes (p&gt;0,05). Nas outras variáveis ocorreu diferença significativa (p&lt;0,05) com o tendão calcâneo apresentando valores maiores para energia e alongamento. O módulo de elasticidade, significativamente maior no ligamento da patela (p&lt;0,05), foi a variável que melhor caracterizou a diferença do comportamento mecânico dos dois materiais.

Statnamic testing of model piles in a clay calibration chamber

The rate of load application during a Statnamic pile test lies between that for static and dynamic pile tests. Current analysis methods offer excellent correlation between Statnamic and static test results for coarse-grained soils. However, over-prediction of pile load capacity can be obtained for fine-grained soils. It is very difficult to explore this anomaly using full scale field tests because of natural soil variability, so a study has been carried out using a model pile installed in similar clay beds prepared in a large triaxial calibration chamber. The instrumented model pile has been loaded at varying rates by a computer controlled servo-hydraulic actuator. The tests have simulated static loading, constant rate of penetration at various rates of penetration, and Statnamic loading. Results suggest that components of the rate effect associated with increased pile penetration rates may be described by a power law relationship.

Forcing Chromatin

Forcing Chromatin

Prediction of Asphalt Rheological Properties Using HP-GPC

Asphalt cement is a rheological material because its deformation characteristics vary not only with load but also with rate of load application. The chemical composition of asphalt cement affects its behavior. One of the methods that has been developed to study the molecular structure of materials is high pressure-gel permeation chromatography (HP-GPC). In this paper, the possibility of using the HP-GPC chromatograms to predict asphalt rheological properties is evaluated. Mathematical models are generated to predict the rheological properties of asphalt cement based on its molecular size. In the Gulf countries, there are currently four asphalt-producing refineries that include Ras Tanura and Riyadh refineries in Saudi Arabia, Al-Ahmadi refinery in Kuwait, and Bapco refinery in Bahrain. The asphalt produced by those refineries is referred to as “Arabian asphalt,” For this study to be comprehensive, it was decided to collect asphalt samples from all those refineries. Another set of polymer modified asphalt samples with 5, 10, and 15% crumb rubber and 3, 6, and 9% styrene-butadiene-styrene was included in this study to evaluate the effect of polymer modification on the molecular size distribution of the asphalt samples.

Performance-based characterization of Arab asphalt

Asphalt binders are elasto-visco-elastic materials where temperature and rate of load application have a great influence on their behavior. They are classified as rheological materials since their stress-strain response is both time and temperature dependent. Asphalt binder consistency and hence ability to sustain and hold its fundamental cementing mechanism changes depending on temperature. In this research, the physical and rheological properties of the locally produced Arab asphalt binders and the performance requirements of the Gulf countries environmental conditions were determined. The designed experiments and the collected data clearly indicated that the locally produced asphalt binders can be used without modification in areas where the maximum pavement temperature does not exceed 64 °C. Temperature zoning indicated that more than 50% of the Gulf countries areas experience a maximum pavement temperature of 76 °C. Therefore, asphalt binder modification is required to meet Gulf countries' performance requirements.