Loading Rate Dependence Research Articles

メタンハイドレートを含む模擬堆積物の三軸圧縮特性におよぼすひずみ速度の影響

Methane hydrate is anticipated to be a promising energy resource of natural gas, since a large amount of reservoir exists in marine sediments or in permafrost regions worldwide. In order to evaluate a productivity of methane gas from methane hydrate reservoirs, it is necessary to develop a gas production numeric simulator. And, for precise assessment of long-term gas productivity, it is important to consider time-dependent properties of sediments containing methane hydrate.In this study, loading rate dependency, one of important time-dependent properties, of artificial sediment containing methane hydrate was experimentally examined. Results of triaxial compression tests of water-saturated Toyoura sand (saturated-sand specimen) and Toyoura sand containing synthetic methane hydrate (hydrate-sand specimen), at conditions of confining pressure 9MPa, pore water pressure 8MPa and temperature 278K, were presented. Loading was conducted at a constant strain rate or alternating strain rate. In constant strain rate test, specimen was loaded at strain rate of 0.1%/min, 0.05%/min and 0.01%/min. In alternating strain rate test, one specimen was loaded at a strain rate alternated between the lower rate C1 and the higher rate C2 at strain intervals Δe. The conditions of C1, C2 and Δe were briefly examined in this study.Experimental results indicate that saturated-sand specimen shows very weak strain rate dependency suggesting that, in most cases, time-dependency is negligible small. Strain rate dependency of the peak strength for hydrate-sand specimen was considerably stronger than that of saturated-sand specimen. Referring to earlier works, the time-dependency of hydrate-sand specimen seemed to be weaker than that of ice or methane hydrate and comparable with that of frozen sand.

Triaxial-Compression Testing Method Developed for Small Rock Specimens

Estimation of physical properties of rock is essential to design rock structures and to evaluate the stability of rock slopes. It is well known that rock properties often vary from site to site, and even from specimen to specimen. So, in many cases, it requires many rock samples, much effort and cost to obtain the reliable data. In this study, an efficient testing method with small rock specimens was proposed and examined. At first, the preparation process for a cylindrical specimen, 10mm in diameter and 20mm in length, was developed. In the experimental work, the transparent triaxial vessel, developed by Okubo et al., was modified and used for the small specimen. Triaxial compression tests with constant loading rate were conducted with small specimens of Tage tuff, and it was found that cohesion, C, and angle of internal friction, φ, can be precisely obtained. By this test, the loading rate dependency of a stress-strain curve can be also obtained by just one small specimen with the loading rate alternately switching during a test. Small specimens are easy to carry and it is effective especially for geophysical researches in foreign countries. So, in this study, triaxial compression tests, noted above, were also conducted with rocks obtained around the Three Gorges Reservoir in China.

Characterization of Shear Banding in La-Based Bulk Metallic Glasses through Indentation

La64Al14(Cu,Ni)22, La63.1Al15.2(Cu,Ni)21.7, La57.6Al17.5(Cu,Ni)24.9, and La55Al25Cu10Ni5Co5 bulk metallic glasses (BMGs) with low glass transition temperature (Tg) were prepared by copper-mould casting method. The homologous temperature (the ratio of room temperature to Tg) of the four BMGs ranges from 0.64 to 0.73. Plastic deformation behavior of the BMGs at various loading rates was studied by nanoindentation. The results showed that the loading rate dependency of serrated flow, which is related to the nucleation and propagation of shear bands, depends strongly on the homologous temperature. The alloys with relatively high homologous temperature exhibit an increase in flow serration with increasing loading rate, whereas, the alloys with low homologous temperature exhibit prominent serrations at low rates. No distinct shear band is observed around the indents for all alloys after nanoindentation at all the studied loading rates. Alternately, shear band pattern are characterized through macro-indentation, which shows that shear band spacing decreases with the increase of the homologous temperature.

Durability of polymer matrix composites: Viscoelastic effect on static and fatigue loading

The structural applications of polymer matrix composites (PMC) demand lifetimes of 15, 25 and 50 years. However, the mechanical properties of these composites have a time dependent nature, i.e. strength and stiffness are time-dependent due to the hereditary nature (viscoelasticity) of polymers. In this context lifetime models for viscoelastic materials, i.e. energy-based criteria and fracture mechanics extended to viscoelastic media, are revised. These models are applied to predict the lifetime of composite materials under special cases of constant load (creep rupture) and constant stress rate to failure. It is verified that these lifetime theories predict similar relationship between creep failure and constant stress rate failure strength. Alternative approaches based on Strength Evolution Integral [Reifsnider KL, Stinchcomb WW. A critical element model of the residual strength and life of fatigue–loaded composite coupons. In: Hahn HT, editor. Composite materials: fatigue and fracture (ASTM STP 907). Philadelphia (PA): American Society for Testing and Materials; 1986. p. 298–313; Reifsnider KK, Case SC, Duthoi J. The mechanics of composite strength evolution. Compos Sci Technol 2000; 60:2539–46; Reifsnider KK, Case SC. Damage tolerance and durability in material systems. Wiley-Interscience; 2002] and on Linear Damage Accumulation (LCD) law confirm these results. In addition the LCD law was found to be generally unsatisfactory except for the special case of constant stress rate to failure. Accordingly this result validates the accelerated methodology proposed by [Miyano Y, McMurray M, Enyama J, Nakada M. Loading rate and temperature dependence on flexural fatigue behavior of a satin woven CFRP laminate. J Compos Mater 1994;28(13):1250–60; Miyano Y, Nakada M, McMurray MK, Muki R. Prediction of flexural fatigue strength of CRFP composites under arbitrary frequency, stress ratio and temperature. J Compos Mater 1997;31(6):619–38; Miyano Y, Nakada M, Kudoh H, Muki R. Prediction of tensile fatigue life for unidirectional CFRP. J Compos Mater 2000;34(7):538–50; Miyano Y, Nakada M, Sekine N. Accelerated testing for long-term durability of GFRP laminates for marine use. Compos: Part B 2004;35:497–502; Miyano Y, Nakada M, Sekine N. Accelerated testing for long-term durability of FRP laminates for marine use. J Compos Mater 2005;39(1):5–20], which is based on LCD law, to characterize long-term creep failure of polymer composites based on the constant stress rate failure strength curves. Finally a new formulation is proposed, based on Strength Evolution Integral, to predict of fatigue failure load for an arbitrary load ratio.

Effects of nonlinear viscoelastic behaviour and loading rate on transverse cracking in CFRP laminates

The progressive multiplication of matrix transverse cracks in cross-ply laminates made of long carbon fibre reinforced polymer (CFRP) is addressed in this study. Monotonic tensile tests performed on [03/903]S laminates at 120°C have shown a marked dependence of cracking development on loading rate. This paper aims to assess the impact of the material nonlinearity on the loading rate sensitivity of the damaging process. A “shear-lag” damage analysis, using the nonlinear correspondence principle and appropriate failure criteria, is carried out to numerically predict the cracking evolution. This work shows that, though important, the material nonlinearity of the undamaged material does not significantly enhance the loading rate sensitivity of the cracking process and it cannot explain alone the phenomenon. On the other hand, taking into account the loading rate dependence of the critical strength, together with the R-curve effect, which gives good predicted cracking curves, suggests that the observed rate effect pertains to the viscoelastic character of the damaged material in the process zone close to crack fronts.

A study of tensile damage and attenuation effect of perforated concrete defense layer on stress waves

Civil defense shelters are often constructed beneath the ground to provide protection against blast loadings. Concrete is widely used as the material for the defense layer of the shelters. This paper adopts a continuum damage model of brittle media to numerically investigate the dynamic fracture and attenuation effect of perforated concrete defense layer on stress waves from planar charge. The model includes damage accumulation and loading rate-dependence, and has been succinctly implemented into the dynamic finite element code, LS-DYNA, via its user defined subroutine. The numerical results reveal that the adopted model can well predict the tensile damage owing to the reflection of pressure waves from cavities and free boundaries. Again, the elastoplastic properties of concrete play significant roles in the stress-wave attenuation and the peak values of hydrostatic pressure beneath a circular cavity are largely reduced. One empirical formula is finally proposed to relate the decay factor of peak hydrostatic pressure to the cavity dimensions and relative position.

Effect of strain rate on the interlaminar fracture toughness of Zanchor reinforced composites

The interlaminar fracture behavior of Zanchor, which is a novel out-of-plane reinforcement technique developed by Mitsubishi Heavy Industries and Shikibo, reinforced composite laminates was studied to clear the mechanism of Zanchor reinforcement, where the effects of loading mode and loading rate on fracture behavior were mainly focused on. The mode I test results showed that the mode I fracture toughness of the Zanchor reinforced composites considerably decreased with increasing loading rate, where the reduction of mode I interlaminar fracture toughness at higher loading rates was a consequence of the loading rate dependence of microscopic fracture behavior. On the other hand, mode II test results showed that the mode II fracture toughness of the Zanchor reinforced composites increased with increasing loading rate, where the reinforcing mechanism of Zanchor under mode II loading was basically different from that under mode I loading.

탄소나노튜브의 역학적 거동에 관한 온도와 하중부하속도의 의존성

The temperature and loading-rate dependence on the mechanical behavior of single-walled carbon nanotubes under axial compression and torsion is examined with classical molecular dynamics simulation. The critical buckling is found to depend on the temperature and loading-rate. The yielding under torsion is also found to depend on the temperature and loading-rate. But it is shown that the compression and torsional stiffness are independent of the varied temperatures and loading-rates.

Deformation behavior during nanoindentation in Ce-based bulk metallic glasses

The deformation behavior and the effect of the loading rate on the plastic deformation in Ce-based bulk metallic glasses (BMGs) were investigated through nanoindentation tests. The results showed that the loading rate dependence of plastic deformation during nanoindentation measurements in the Ce-based BMGs is quite unique in contrast to that of other BMG alloys. The load-displacement (P-h) curves of Ce60Al15Cu10Ni15 BMG exhibit a homogeneous plastic deformation at low loading rates, and a prominent serrated flow at high strain rates, whereas, the P-h curves of Ce65Al10Cu10Ni10Nb5 exhibit homogenous plastic deformation at all studied loading rates. The room temperature creep behavior could clearly be observed in these two alloys. The mechanism of the unique plastic deformation feature in the Ce-based BMGs was studied.

Uniaxial compression and tension tests of anthracite and loading rate dependence of peak strength

The mechanical characteristics of coal under uniaxial compressive stress and uniaxial tensile stress are key factors in investigations of the stability of galleries and coal faces, and are vital considerations for the efficient design of coalmines, disaster prevention, and environmental preservation. These mechanical characteristics have long been a topic of research, but remain insufficiently understood. In this study we performed uniaxial compression tests and uniaxial tension tests on coal, with particular attention to two concerns. The first was to measure the loading rate dependence of the peak strength of coal. Coal shows high sample-to-sample scatter in strength; test methods that are successful in comparatively homogeneous rock types cannot be used for coal. We therefore used an alternative test method that was recently developed by the authors. Anthracite samples were subjected to alternating slow and fast strain rates. Measured variations in stress during this process were used to estimate the loading rate dependence of peak strength. The second objective was to obtain complete stress–strain curves for coal under uniaxial tensile stress. It is difficult to hold samples secure during a tensile test; consequently, such curves have yet to be obtained. This study presents a successful application of the authors' method to the analysis of coal samples, yielding a complete stress–strain curve under tensile stress. The two methods presented here hold promise for application not only to anthracite but also to a wide variety of coals. It is possible to derive the values of the constants used in constitutive equations from the obtained experimental results. Once these equations are determined, they can be incorporated into finite-element software to investigate various time-dependent behaviors of coal and aid in the efficient design of coalmines and the prevention of subsidence and mine disasters.

Effects of loading rate on the deformation and cracking of dental multilayers: Experiments and models

The paper presents the results of combined experimental, analytical, and computational studies of contact-induced deformation and cracking in dental multilayers. These include studies of individual layers and composite structures that consist of tri-layers of glass bonded to ceramic-filled polymer foundation with an acrylate-based join material. Loading-rate-dependent Young's moduli of the join and foundation materials were obtained from monotonic compression tests. Critical loads were also determined for the tri-layers from Hertzian contact tests at different loading rates. The fracture onset (sub-surface radial cracking) was detected using an in situ telescope. The measured rate-dependent Young's moduli were then incorporated into a finite element model that was used to predict the rate-dependent critical loads in the tri-layer system. Finally, the paper shows that the observed loading rate-dependence of the critical load (for radial cracking) is due to the combined effects of slow crack growth in glass and rate-dependent Young's moduli in the join and foundation layers.

A new testing method for investigating the loading rate dependency of peak and residual rock strength

One of the important methods for investigating viscoelasticity is to measure the loading-rate dependency of peak strength; however, no experimental method has been established for accurately measuring the loading-rate dependency of peak strength from a small number of samples. In this study we propose such a method. A single sample is loaded at alternating strain rates to obtain stress–strain curves for both strain rates. The loading-rate dependency of peak strength obtained via this method was compared with the findings of conventional methods. The loading-rate dependency indicated for Tage tuff, Sanjome andesite and Akiyoshi marble was nearly identical to previous results obtained using conventional methods, including results obtained under confining pressure. The loading-rate dependency of peak strength in these experiments shows a close relation with the creep stress-dependency of creep life. We also investigated the loading-rate dependency of the stress–strain curve for the post-failure region for which few results have been published. Under confining pressure, the corrected stress–strain curve, obtained by multiplying the stress of the complete stress–strain curve obtained at the fast strain rate by a constant determined by the ratio between the fast strain rate and slow strain rate, is nearly coincident with the stress–strain curve for the slow strain rate. This is an interesting result and represents new knowledge that may help elucidate failure mechanisms in the post-failure region. The loading-rate dependency of stress in the alternating strain rate experiment proposed here was most clearly observed when the stress–strain curve becomes flat, parallel to the strain axis. Some improvements to the proposed method are required to enable accurate investigations of loading-rate dependency during low stresses immediately after initiation of loading or during the abrupt decreases in stress that occur following peak strength.

312 SKD61材およびS45C材に対する破壊靱性の負荷速度依存性について(損傷評価および破壊力学)

312 SKD61材およびS45C材に対する破壊靱性の負荷速度依存性について(損傷評価および破壊力学)

Dynamic force spectroscopy of the digoxigenin–antibody complex

Small ligands and their receptors are widely used non-covalent couplers in various biotech applications. One prominent example, the digoxigenin–antibody complex, was often used to immobilize samples for single molecule force measurements by optical trap or AFM. Here, we employed dynamic AFM spectroscopy to demonstrate that a single digoxigenin–antibody bond is likely to fail even under moderate loading rates. This effect potentially could lower the yield of measurements or even obscure the unbinding data of the sample by the rupture events of the coupler. Immobilization by multiple antibody–antigen bonds, therefore, is highly recommended. The analysis of our data revealed a pronounced loading rate dependence of the rupture force, which we analyzed based on the well-established Bell–Evans-model with two subsequent unbinding barriers. We could show that the first barrier has a width of Δ x 1 = 1.15 nm and a spontaneous rate of k off1 = 0.015 s −1 and the second has a width of Δ x 2 = 0.35 nm and a spontaneous rate of k off2 = 4.56 s −1. In the crossover region between the two regimes, we found a marked discrepancy between the predicted bond rupture probability density and the measured rupture force histograms, which we discuss as non-Markovian contribution to the unbinding process.

Interactions between cargo-carrying biomolecular shuttles

Microtubule shuttles propelled by the motor protein kinesin embedded in self-assembledmonolayers are being developed for active transport functions in artificial microfluidicsystems. As a model system, biotinylated microtubules have been laden withstreptavidin-coated particles as cargo. The behaviour of cargo-laden microtubules has beenobserved using fluorescence microscopy upon activation of kinesin-driven transportprocesses. Collisions between mobile microtubules and their particulate cargo result in sixdistinct behaviours: bypass, microtubule bending, particle knock-off, particletransfers between microtubules, co-joining of microtubules to a common particle, andparticle-induced severing of microtubules. The distribution of observed events can bedescribed qualitatively on the basis of the mechanics of motor proteins and microtubules,the geometry of the collision events, and the loading rate dependence of the strength ofmicrotubule–particle binding. Implications of the results for the use of motor proteins inactive transport and cargo-handling systems for nanomaterials are described.

Multilayer Microcapsules as Anti‐Cancer Drug Delivery Vehicle: Deposition, Sustained Release, and in vitro Bioactivity

A drug delivery system based on spontaneous deposition of soluble, low-molecular-weight therapeutic agents has been developed for the purpose of sustaining drug release. Layer-by-layer assembly of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) colloidal particles, followed by removal of the cores at low pH has yielded intact hollow microcapsules having the ability to induce deposition of various water-soluble substances. Dynamic observation by confocal laser scanning microscopy provided direct evidence of such deposition. Dependence of loading rate on molecular weight was investigated. Efficient loading of an anti-cancer drug, daunorubicin (DNR), was confirmed by transmission electron microscopy (TEM). Its release was quantified by fluorometry. The results indicated that loading, and subsequent release, could be tuned by factors such as feeding concentrations, temperature, and salt concentrations. The intrinsic mechanism of loading and release was discussed taking into account the interaction between the drugs and the poly(styrene sulfonate)/MF complex existing in the hollow capsules. With culture of the HL-60 cell line, a kind of human leukemia cell, the presence of DNR-loaded capsules was seen to steadily decrease the cyto-viability. Fluorescence intensity averaged from inside the circles as a function of incubation time.

Effects of Temperature and Loading Rate on Fracture Toughness

It is known that fracture toughness value is affected by test temperature, specimen thickness and loading rate. In the present study, specimen size and test temperature are varied widely with the obtained data then being analyzed using rate parameter. Additionally, the fracture toughness values are obtained using round bar-type specimen with a circular notch. This result is compared with the result of the CT specimens, and the advantage of using the round bar-type specimen with a circular notch to modify specimen size requirement is discussed. Sample material used is HT780 high tensile strength steel. The test specimens were 1T, 2T and 4T-CT that are described in ASTM E399. Notched round bar-type specimen with a diameter of 15mm and notch root radius of 0.25mm is also used. The test temperature is varied from a low temperature to room temperature, and loading rate is varied about the 1T-CT specimen and the notched round bar-type specimen between static and 1000mm/sec. The test temperature and the loading rate dependency of the fracture toughness values were arranged by the rate parameter. The fracture toughness value has decreased with the decrease in test temperature and with the increase in specimen thickness and loading rate. The fracture toughness value obtained from the notched round bar-type specimen indicated a value close to 2T-CT specimen. It is shown that valid fracture toughness value can be obtained with a small test specimen by the notched round bar-type specimen. The test temperature and the loading rate dependency of the fracture toughness values can be successfully arranged by the rate parameter that can express both temperature and strain rate dependencies. Feasibility of using round bar-type specimen to obtain valid fracture toughness values with less specimen mass was demonstrated.

Ratcheting behavior of PTFE under cyclic compression

In this paper, loading rate dependence of stress–strain response and ratcheting behavior under compression for PTFE were studied. The effects of loading rate, mean stress and stress amplitude on the ratcheting behavior of PTFE are discussed. It is shown that PTFE is a rate dependent material, but it is insensitive to loading rate when the rate is higher than 40 N/s. Ratcheting strain increases as the loading rate decreased. When loading rate is higher than 40 N/s, there is little effect of loading rate on ratcheting strain rate. At the same stress amplitude (mean stress), the ratcheting strain and ratcheting strain rate increase as mean stress (stress amplitude) increased.

Forced Kramers escape in single-molecule pulling experiments

The pulling-induced rupture of noncovalent bonds is studied by the overdamped Kramers theory with full account of a time-varying barrier. Mechanic pulling reduces the energy barrier and leads to loading-rate dependence of the rupture force F(u)(F(t)). Tested against Langevin dynamics, four distinct regimes are identified, including kinetic dominant, weak pulling, strong pulling, and mechanic pulling dominant. Asymptotic analyses show that F(u) approximately ln F(t) in weak pulling regime and becomes 1-(F(u)F(c)) approximately [ln(F(t))E(b)](23) in strong pulling regime. Kinetic informations such as activation energy E(b) and critical force F(c) were extracted from pulling experiments for biotin-streptavidin complex.

Quantifying Adhesion Bond Parameters to Distinguish Interactions of Hydrophilic and Hydrophobic Blocks of Polystyrene−Poly-2-vinylpyridine with a Silicon Nitride Surface

An analysis of the loading rate dependence of the forces required to rupture an AFM tip from a block copolymer surface has provided insight into the structure of the surface-macromolecule contact, differentiation of the block contacting the tip, a measure of the polymer-surface binding energy, and the rigidity of the contact. Polystyrene-poly-2-vinylpyridine block copolymers were studied adsorbing to silicon nitride. Polystyrene makes stiff van der Waals contact with the silicon nitride surface in aqueous solution, while the bond of poly-2-vinylpyridine to the surface is more flexible and may involve a bridging water.