Small Strain Levels Research Articles

Asphalt binder characterization using waveform-based viscoelastic measures and time-temperature superposition principle under large strains

In the United States, currently peak-to-peak oscillatory shear stress-strain data is used in the asphalt binder characterization protocols. This practice necessitates the measurement, usage, and reporting of only peak responses for material characterization and specification even though a sinusoidal waveform is applied. However, in this paper it is argued that with the proliferation of modified binding systems, it is critical to capture and examine the complete waveform data when subjected to both small and large strains. This approach will help properly differentiating between materials. In this study, four modified binders were tested at small and large strain levels while recording the complete response waveform. The recorded waveform data was then used to examine the linear and nonlinear viscoelastic characteristics of these binders. The orthogonal stress decomposition technique was used to delineate elastic and viscous contributions in the nonlinear regime. This study examined the time-temperature dependency under both linear and nonlinear regimes. The time-temperature shift factors obtained from linear regime were effectively applied in the nonlinear regime. Further, all the tested binders showed strain stiffening and shear thinning behavior under most of the testing conditions. This study provides useful insights about the material behavior under nonlinear regime and can serve as a benchmark for further investigation of nonlinear viscoelastic behavior of asphalt binders.

Small-strain characterization of Shanghai clays by triaxial compression tests

The mechanical properties of the upper Shanghai Layers 2-6 clays at small strain levels have been extensively investigated. Nonetheless, limited data exist on their small-strain characteristics through K 0-consolidated undrained triaxial compression tests, with even less information available for the deeper layers 8 and 10. This study employed a series of K 0-consolidated undrained TC tests on intact samples from both the upper layers 2-6 and the deeper layers 8 and 10 of Shanghai clay. We evaluated the undrained maximum secant stiffness (Eu max) and reference shear strain (γ0.7 ). An increase in over-consolidation ratio (OCR) results in a higher E u max/p’ and a more rapid decay of the G/G max with the increasing shear strain (γ). As the value of γ 0.7 increases with I p and decreases with OCR, a correlation between γ 0.7 and Ip can be established. This study observed significant correlations between the E u max, effective stress (p’), and the maximum deviatoric stress, as well as between E u max and the cone resistance obtained from field cone penetration tests. These correlations offer methods to estimate E u max and γ0.7 values based on parameters that are more readily measurable, which provide critical references for the calculations and design parameters in foundation engineering within the Shanghai region.

Achieving high strength-ductility synergy via Guinier-Preston zone formation in a new Mg–Zn–Al–Ca–Mn–Ce sheet alloy

ZAXME11100 (Mg–1Zn–1Al-0.5Ca-0.4Mn-0.2Ce, wt.%) is a recently developed sheet alloy with excellent formability at room temperature. The yield strength of this alloy is significantly improved by a short 1-h aging treatment at 210 °C (T6), from 159 MPa in solution-treated state (T4) to 270 MPa in the T6 condition, with a slight reduction in tensile elongation (from 31 % in T4 to 26 % in T6). In this work, precipitation microstructure was characterized to explain the aging hardening and high strength-ductility synergy of the new alloy. A high density (8 × 1023/m3) of ordered monolayer Guinier-Preston (GP) zones enriched in Al, Ca and Zn uniformly form on the Mg basal planes after T6 treatment. Grain boundary segregation of Al, Ca and Zn is also observed. Deformation microstructure of T4 and T6 samples tested to various strain levels was examined. At small strain levels, basal and non-basal <a> dislocation slip dominates the deformation process, and cross slip of <a> dislocations between basal and non-basal planes is observed in T6 samples. The GP zones are gradually destroyed by plastic deformation. Based on those results, the strengthening contribution of ordered GP zones was modeled to be 116 MPa. Therefore, formation of GP zones is an effective way to achieve high strength-ductility synergy in wrought Mg alloys.

On the determination of viscoelastic properties of EPP foam in dependence on pre-strain and loading direction

Understanding the viscoelastic properties of EPP foams is of crucial importance for their use in industrial applications. However, mechanical testing of polymeric foams is challenging due to the difficulties that arise from their morphology. For this reason, here currently available DMA methods using a single drive and a multi-drive rheometer as well as multiple loading directions are investigated in detail. Experimental challenges are highlighted and discussed with regard to foam-specific properties. Special focus is laid on the influence of compressive pre-strain. Based on the results, guidelines to perform reproducible DMA tests on the investigated type of material are derived. In addition, the results give deeper insight into the deformation behavior of bead foams at small strain levels and reveal an early onset of the transition from linear to plateau regime.

Boosting the Output Performance of the MoS2 Monolayer-Based Piezoelectric Nanogenerator by Artificial Dual Strain Concentration.

Piezoelectric nanogenerators (PENGs) with molybdenum disulfide (MoS2) monolayers have been intensively studied owing to their superior mechanical durability and stability. However, the limited output performance resulting from a small active area and low strain levels continues to pose a significant challenge that should be overcome. Herein, we report a novel strategy for the epoch-making output performance of a PENG with a MoS2 monolayer by adopting the additive strain concentration concept. The simulation study indicates that strain in the MoS2 monolayer can be initially augmented by the wavy structure resulting from the prestretched poly(dimethylsiloxane) (PDMS) and is further increased through flexural deformation (i.e., bending). Based on these studies, we have developed concentrated strain-applied PENGs with MoS2 monolayers. The wavy structures effectively applied strain to the MoS2 monolayer and generated a piezoelectric output voltage and current of around 580 mV and 47.5 nA, respectively. Our innovative approach to enhancing the performance of PENGs with MoS2 monolayers through the artificial dual strain concept has led to groundbreaking results, achieving the highest recorded output voltage and current for PENGs based on two-dimensional (2D) materials, which provides unique opportunities for the 2D-based energy harvesting field and structural insight into how to improve the net strain on 2D materials.

Experimental Wave-Based Assessment of Liquefaction Resistance for Different Degrees of Saturation

Abstract This paper presents the results of an experimental program carried out in the laboratory aimed at assessing the liquefaction resistance by correlations between longitudinal wave (P-wave) and shear wave (S-wave) velocities (VP and VS) and cyclic stress ratio from triaxial testing (CSRCTx) for different degrees of saturation (Sr). The liquefaction resistance was assessed using a cyclic triaxial apparatus equipped with Hall-effect transducers and bender elements, combining stress-based (large-strain level) and wave-based (small-strain level) approaches. These tests were carried out in soil specimens at relatively high degrees of saturation, which were estimated during testing by VP measurements interpreted using Biot’s theory. The results revealed that, for the same relative density and confinement stress, the S-wave-based approach did not predict the liquefaction resistance well because of the negligible variation in the stress state and soil stiffness for the assessed Sr values, which were above the air-entry value. In turn, the P-wave-based approach effectively predicted the liquefaction resistance increment of the TP-Lisbon sand for different Sr conditions because of the strong dependency of P-wave propagation on the degree of saturation in granular media. This is a consequence of the most relevant factor conditioning the pore pressure buildup in partially saturated sands, e.g., the compressibility of the occluded air bubbles, which can be detected by VP but not by VS.

Damage-Induced Softening of the Sclera: A Pseudo-Elastic Modeling Approach

Abstract The biomechanical properties of the sclera such as the stiffness, anisotropic behavior, and nonlinear stress–strain relationship have been extensively investigated for the pathogenesis study of ocular diseases. Even so, scarce mechanical investigations have been conducted on the damage in the sclera when subjected to large and repetitive deformations. Hence, the aim of this study is to quantify microstructural damage of the posterior and anterior sclera, through mechanical testing and model fitting. We performed uniaxial mechanical tests on scleral strips dissected from African green monkeys. Samples were subjected to strain-driven cycles of 5%, 10%, 15%, and 20% to evaluate the damage behavior commonly known as the Mullins effect. Experimental results showed qualitative changes in the stress–stretch curves when higher loading cycles were applied. A pseudo-elastic model accurately captured the curve trends across all tested samples, as indicated by a coefficient of determination above 0.96 and a subsequent finite element analysis (FEA) validation. Damage evolution and resultant permanent set demonstrated that considerable microstructural failure was attainable even at small strain levels and that the inherent plasticity had a similar contribution to stress-softening as the Mullins effect. Computed material and damage properties are expected to provide a broader understanding of the underlying mechanisms of ocular diseases and the development of more effective approaches for their treatment.

Geomechanical Characterization of Crushed Concrete–Rubber Waste Mixtures

The present study investigates the dynamic and cyclic behavior of mixtures of waste materials, i.e., rigid anthropogenic mineral aggregates (RCA) mixed with recycled soft particles (RTW), based on a series of standard resonant column tests and cyclic torsional shear tests. The laboratory tests presented in this article are part of a larger research project that aims to provide useful insights to facilitate the application of RCA–RTW compositions as geotechnical materials. The impacts of various parameters including shear strain, mean effective stress, and, in particular, rubber content on the shear modulus (G), and damping ratio (D), are considered in detail. Rubber content is considered by the percentage of rubber in the mix weight. In general, the results show that as the RTW content increases, the shear modulus decreases while the damping ratio increases. The largest reduction in the G−modulus values occurs for the highest rubberized mix. The observed damping ratio for pure RCA is approx. three times lower versus rubber-reinforced specimens. The compliance of the behavior of the new RCA–RTW mixtures and pure recycled concrete waste tested under dynamic and cyclic loading is demonstrated. The effects of crushing of the RCA material itself during cyclic loading are visible, and dilution of this process due to the addition of rubber. Furthermore, the test data reveal that the values of the G−modulus and D−ratio at small and medium strain levels are considered independent of the time of vibration.

Self-organized mycelium biocomposites: Effects of geometry and laterite composition on compressive behavior

This study investigates the compressive deformation and the effect of structural architecture on the compressive strength of bioprocessed mycelium biocomposites reinforced with laterite particles. In the mycelium blocks, lignocellulosic hemp hurds function as reinforcing and nutritional substrates. The mycelium acts as a supportive matrix, binding the hemp hurds and the laterite particles which are integrated for further reinforcement to improve the compressive strength of the composite. The compressive behavior of the composites is elucidated using a combined approach of experimental and theoretical studies. The deformation mechanisms are investigated via in-situ observations of the specimens under uniaxial compressive loading. The experiments show that the compressive deformation results in progressive micro-buckling in slender specimens, whereas thicker samples exhibit a soft elastic response at small strain levels followed by continuous stiffening at larger strains. Based on the experimental observations and the morphological characterization, a column buckling analysis was developed for the mycelium-hemp composites to further explain the observed deformation phenomena.

Comparison of damping performance of an aluminum bridge via material damping, support damping and external damping methods

Damping property is the basic energy dissipation mechanism that widely exists in almost all kinds of structures or components. This paper presents an experimental study on three different measures including rubber sheet pavements, rubber bearings and external passive damper to increase the damping of a lightly damped aluminum bridge. These methods are conventional treatments in engineering practice, and they aim to take effect through the aspects of material damping, support damping and external damping, respectively. The performance of these methods in damping increment is compared, and the possible damping mechanism of each measure is discussed. The external damper is found to be most effective in damping increment, followed by rubber bearings. The method of rubber sheet pavement is inefficient in damping increment owing to the huge difference in elastic modulus between aluminium and rubber. The rubber sheet keeps in tiny strain state during structural vibration and fails to generate effective internal friction between particles, and thus contributes little to the overall material damping. This indicates that the damping material method can take effect only if the damping layer has not only remarkable loss factor but also comparable elastic modulus with the target structure. In addition, the external damper generally follows the linear viscous damping law. The external damper having liquid viscosity of 3.05 Pa·s can increase the system damping to 1.5 %, which is almost one order greater than the performance of rubber sheet pavement and rubber bearing methods. Moreover, the external damping method is found to be sensitive to the installation location of the damper. The greater the modal displacement, the larger the system damping is. Furthermore, the system damping is not sensitive to structural frequency, whereas it slightly increases with the structural strain in small strain levels.

Parametric Study of Twin Tunneling Effects on Piled Foundations in Stiff Clay: 3D Finite-Element Approach

Due to urbanization, development of society, and growth of population, there are new demands for tunneling technique to facilitate the public transport as well as high-rise buildings to accommodate an increasing population. Piled foundations are commonly preferred for the construction of high-rise buildings. It is, therefore, unavoidable that tunnels must be constructed near extant buildings resting on piled foundations. Inevitable movement of the ground due to stress changes induced by a tunnel can induce additional settlement and reduce the load-carrying capacity of nearby pile foundation systems. This numerical parametric study investigates the responses of two-by-two piled raft to twin side-by-side tunnels either near the mid-depth of the pile shaft or adjacent to or below the pile toe in stiff clay. In addition, it investigates the effects of different group configurations of the piled raft and elevated pile group. The ground in all the finite-element analyses was modeled using the hypoplasticity (clay) model because of its ability to capture degradation of soil stiffness at a small-strain level. Twin tunneling below the pile and near the middepth of the pile shaft caused the largest and smallest settlement of the piled raft, respectively. Unlike induced piled raft settlement, the most significant transverse tilting of the raft is induced after the advancement of the first tunnel. After the twin tunneling near the pile shaft was completed, the raft was separated from the ground, and a portion of the working load carried by the raft was transferred to the piles. The computed results have revealed that the induced settlement of the elevated pile group was significantly larger than that of the piled raft. A significant effect number of piles in the group was found on the piled raft responses to tunneling.

Shear modulus and damping ratio of saturated coral sand under generalised cyclic loadings

The influence of complex cyclic loadings associated with earthquakes on the shear modulus and damping properties of saturated coral sands has yet to be established. This paper presents comprehensive data sets from multi-staged strain-controlled (denoted Mγ), constant-amplitude strain-controlled (Cγ) and variable-amplitude strain-controlled (Vγ) undrained cyclic triaxial (UCTX) tests on a coral sand. The strain-dependent shear modulus and damping ratio from the Mγ UCTX tests and the cyclic stiffness degradation behaviour in the Cγ and Vγ UCTX tests are investigated. A correlation-function-based method is proposed to calculate the secant shear modulus and damping ratio at different strain levels, which shows higher precision at both small and large strain levels compared with the conventional methods. An important finding of the study is that the shear modulus reduction rate of the coral sand is significantly lower than that of siliceous sands, while the damping ratio for shear strain amplitude between 0·01% and 0·1% is well below that of siliceous sands. Two quantities: one is referred to as the strain ratio (ΓN) and used for characterising the normalised cycle-dependent strain amplitude, and the other referred to as the damage energy measure (δN) and used for characterising the cumulative normalised elastic strain energy absorption, are proposed such that a unique formula can be established for predicting the cyclic stiffness degradation in the UCTX tests with different loading patterns. This energy-strain-dependent formula is further validated using independent data from stress- and strain-controlled UCTX tests involving four patterns of cyclic loadings, and a satisfactory performance is demonstrated.

Influence of strain rate on dynamic recrystallization behavior and hot formability of basal-textured AZ80 magnesium alloy

This work investigates the strain rate dependence of deformation and dynamic recrystallization (DRX) behaviors of basal-textured AZ80 magnesium alloy, in the hot compressions at 350 °C with varying strain rates of 10−3 s−1 and 10 s−1. Hot compressed microstructure was characterized using electron backscatter diffraction (EBSD) with grain-based analytical approaches, providing insights into the operative dynamic recrystallization mechanisms and correlated texture evolution. At small strain levels, discontinuous DRX mechanism was dominant at 10−3 s−1 and stress concentrations between the neighboring grains were effectively relieved by grain boundary bulge and growth of DRXed nucleus. In contrast, at 10 s−1, twin-induced DRX and continuous DRX mechanisms were activated. Off-basal-oriented grains (soft) were consumed rapidly by the operative DRX processes, while basal-oriented grains (hard) show less tendency to recrystallize. At the interphase between the residual basal-oriented grain and the neighboring DRXed grains, intergranular micro-cracks initiated in the incipient stage of the hot compression at 10 s−1, due to the absence of effective strain releasing mechanism. The results have implications for hot workability improvement for AZ80 magnesium alloy under high-strain-rate conditions.

Mechanical Consequence Observation and Microscopic Visualization of Internal Erosion Using Developed Plane Strain Erosion Apparatus

Abstract Internal erosion has been frequently reported and has caused failures and instabilities of geotechnical structures. A plane strain erosion apparatus is developed in this study to allow the subsequent conduction of drained compression test after seepage test and the microscopic observation of particle movement through a transparent window. A drained compression test preceded by a seepage test is performed on specimens containing the same initial fines contents to investigate the mechanical consequence impacts of seepage-induced internal erosion. Experimental results reveal that, compared with uneroded soils, internally eroded soils show a larger secant stiffness at a small strain level (∼1 %). At medium strain level (∼15 %), the soils with erosion show smaller deviator stress comparing with soils without erosion. The analysis of images recorded by the microscope proves that the fines contacted with coarse particles possibly transferring the load are distinct between the soils with and without internal erosion at both small and medium strain levels during the drained compression test, which indicates that the soil fabric could affect the mechanical behaviors of soils subjected to internal erosion. Our designed equipment and microscopic observation could throw some light on the research of internal erosion from the view of particle scale.

Experimental study on suffusion under multiple seepages and its impact on undrained mechanical responses of gap-graded soil

An experimental investigation of multiple seepage-induced suffusion and its impact on the mechanical responses of internally unstable gap-graded soil, with a fines content of 25%, is presented in this paper. Using a modified triaxial erosion apparatus, with a redesigned seepage control system, erosion tests under multiple seepage conditions, as well as undrained monotonic and cyclic compression tests, are performed. It is found that multiple seepages cause an eroded mass without a marked change in volume and with a change in hydraulic conductivity as the number of seepage cycles increases. The monotonic compression tests show that eroded soil presents a smaller peak strength, residual strength, and a greater contractive response than non-eroded soil. The peak strength and stiffness of eroded soil are seen to decrease considerably as the number of seepage cycles increases. Multiple seepage-induced suffusion may create a collapsible soil structure in eroded soil, as shown by sudden decreases in deviator stress and stiffness, coupled by sharp increases in pore water pressure at small strain levels. As eroded soil might already be unstable, cyclic loading causes it to collapse, revealing a sudden increase in the generation of cyclic pore water pressure and a decrease in liquefaction resistance. The results highlight the importance of conducting laboratory tests to determine the impact of internal erosion on the strength and liquefaction resistance.

Gecko-inspired ultrasensitive multifunctional mechano-optical smart membranes

Mechano-optical materials are of great importance in smart window, security, display and camouflages. However, fabricating ultrasensitive optical devices with wide range still remains great challenging. Inspired from the fast tail amputation of gecko utilizing weak non-ossificated septum, herein, we report an ultrasensitive mechano-optical membrane based on weak dye layer between silica nanoparticles and soft polydimethylsiloxane matrix. Owing to the light scattering from dye-induced internal cavitation, the transmittance dramatically decreases by ～44% at initial small strain level (15%) and a high sensitivity (S > 2) is kept within an abroad strain range (0～35%). Moreover, a high total transmittance tuning range of ～75% is exhibited. Simulation and experimental monitoring demonstrate the effective weakening of interface energy. The potential applications in smart window, sensor, anti-counterfeiting also exhibit the multifunctionality of our smart membranes. This facile and low-cost approach enables the large-scale production and applications of mechano-optical membranes and this interface design provides a general way to develop ultrasensitive mechano-responsive materials.

Evaluation of small-strain shear modulus of Fontainebleau sand based on innovative pressuremeter probe testing in a calibration chamber

This paper presents an experimental study aimed at evaluating the measuring capabilities of an innovative monocellular pressuremeter probe, the Monocell Francis Cour probe, based on calibration testing in the laboratory. The originality of the tested equipment is to allow evaluation of soil properties in both small- and large-strain domains, without the need of sophisticated point displacement measuring arms. This paper focuses on the evaluation of small-strain shear modulus G of Fontainebleau sand, NE34, based on tests carried out with this specific pressuremeter probe. Shear modulus values obtained with this probe are then compared with values resulting from more classical elementary tests, showing a fairly good consistency. It is shown, with satisfactory agreement, that it is possible to quantify the influence of the density index of the sand as well as the influence of the mean effective stress around the probe on the shear modulus, based on the analysis of specific unload−reload loops performed during the test. The experimental programme carried out under well-controlled laboratory conditions allows a validation to be proposed for a method of derivation of the shear modulus of sand at small strain levels using this prototype pressuremeter.

Viscoelastic characterisation of asphalt concrete under different loading conditions

ABSTRACT Asphalt concrete (AC) is a composite material that exhibits time and temperature-dependent properties, and it is generally accepted that AC behaves as a linear viscoelastic solid at small strain levels. Nevertheless, different mechanisms and the damage evolution can change its behaviour from the linear viscoelasticity. This study was focused on identifying the causes of the deviation of AC viscoelastic properties under different loading conditions and at small strain levels during complex modulus tests. Sinusoidal tension–compression and compression tests on six asphalt mixtures produced with the same aggregate gradation but different asphalt binders under stress- and strain-controlled conditions were performed within a defined range of frequencies and temperatures. It was found that aggregate interaction and energy dissipation characteristics were the main mechanisms that influenced deviations in the viscoelastic properties, but they were only significant at high temperatures and during considerable nonrecoverable accumulated deformation.

Laboratory Evaluation of the Measuring Capabilities of an Innovative Pressuremeter Probe in Dry Sand

Abstract This article presents the experimental procedures performed in a laboratory to evaluate the measuring capabilities of an innovative monocellular pressuremeter probe. This probe takes advantage of recent technological developments in the domain of inflatable membranes currently applied in the so-called Francis Cour standard tricellular probes, which allow covering an expansion range up to large cavity strains. Those improvements were found to enable increasing the accuracy in the assessment of radial expansion through volume injection in the probe measuring cell at relatively small strain levels without the need of sophisticated punctual measuring arms. Assessing this domain via in situ tests makes up a major contribution to the design of geotechnical structures under cyclic loads, for which the current design practice is mainly developed through laboratory soil tests. To reach this final objective, the probe’s validation program was launched based on pressuremeter tests with unload-reload loops performed in a laboratory calibration chamber and in situ on reference testing sites. This paper focuses on the laboratory testing protocols performed in dry Fontainebleau sand specimens. Shear moduli obtained with the pressuremeter are compared with the expected elementary values for this sand, and it is shown that it was possible to assess sand stiffness at a small strain level using this probe under controlled conditions in a laboratory.

Effect of Fiber and Cement Additives on the Small-Strain Stiffness Behavior of Toyoura Sand

The disposal of 2011 Japan earthquake waste has become an important issue in Japan and it is not realistic or economical to send all of these wastes to landfill sites, due to limited space, high costs, and related environmental issues. In sustainable geotechnical applications, mixing of the separated soils from disaster wastes with additives (e.g., cement and fiber) is required to improve their strength and stiffness characteristics. In this study, monotonic triaxial drained compression tests are performed on medium dense specimens of Toyoura sand-cement-fiber mixtures with different percentages of fiber and cement (e.g., 0–3%) additives. The experimental results indicate that behavior of the mixtures is significantly affected by the concentration of fiber and cement additives. Based on a comprehensive set of test results, modifications to the series of equations were developed that can be used to evaluate the shear modulus and mobilized stress curves at small-strain levels. The experimental results and model comparison show that the elastic threshold strain (γe), reference strain (γr), increases with fiber and cement additives. In addition, the range of curvature parameter, from 0.88 to 1.0, provides a good comparison with the results of small-strain measurements. Overall, the comparison of the results and model shows that the small-strain measurements obtained using local strain transducers fall within the range of model upper and lower bound curves. The results of the unreinforced, fiber, and cemented sand shows a close agreement with the model mean curve, but fiber-reinforced cemented sand shows a good comparison with model upper bound.