Large-strain Tests Research Articles

One-dimensional large strain nonlinear thaw consolidation model for saturated frozen soil

Based on the piece-linear finite difference approach, a one-dimensional large strain thaw consolidation model, TCS1, for saturated frozen soil was established. The model couples the heat transfer considering phase change of pore ice with consolidation deformation, and accounts for large strain, soil self-weight, unfrozen water, variable hydraulic conductivity and compressibility, flexible boundary conditions and time-dependent loading during the process of thaw consolidation. The FORTRAN is used to implement computation of the model. TCS1 was verified by the existing numerical solutions and laboratory tests. The results were in good agreement with the large strain numerical solutions and tests results. Computational examples were conducted for further study of the influence of strain value, loading types and periodic temperature boundaries on the thaw consolidation of frozen soil.

Experimental Study on Dynamic Modulus and Damping Ratio of Rubber–Sand Mixtures Over a Wide Strain Range

This paper systematically investigates the dynamic behavior of sandy soils mixed with recycled tire rubber over a wide strain range in the order of 10[Formula: see text]–10[Formula: see text], using combined resonant column and cyclic triaxial tests for measurement of the shear modulus and damping ratio. The experiment integrates small-strain tests using a resonant column apparatus and large-strain tests using a cyclic triaxial apparatus. The results demonstrated that the addition of rubber particles significantly enhances the linear elastic properties of the host sandy soils and improves the critical shear strain from which the rubber–sand mixtures change from linear to nonlinear stress–strain behavior. The critical shear strain is therefore introduced as the function of rubber content (RC), to identify the influence of RC on the strain-dependent dynamic properties of the host sandy soils. Then, a well-calibrated prediction formula is applied in conjunction with the concept of binary packing material to describe the behavior of the host sandy soils with various RC. Remarkably, the obtained normalized shear modulus and damping ratio vs. shear strain relationships address the limitations of existing testing methods to simultaneously capture the soil dynamic properties at low-strain (stiffness) and the large-strain (energy dissipation) regimes. The model constants can be simply determined through a unique set of explicit expressions which incorporate some basic index properties of the host sand and recycled tire rubber. In this regard, the proposed procedure provides a significant advantage in the evaluation of strain-dependent dynamic properties of rubber–sand mixtures in practice.

Prediction of Unloading Failure Strain and Undrained Shear Strength of Saturated Clays by Limit Pressure from Prebored Pressuremeter

Abstract Saturated clays mostly fail in lateral unloading by the reduction of undrained shear strength (Su) because of an increase in lateral unloading strain (εu), which is the most predominant factor affecting the soil mass in excavated structures. An attempt is made to extend the work of Houlsby and Withers (1988) on the self-boring pressuremeter (SBP) and Ferreira and Robertson (1994) for the full-displacement pressuremeter (FDP) and SBP, for unloading curves of the prebored pressuremeter (PBP) test for large strain (up to 41.5 %) tests in a specific type of soil (i.e., saturated lean clay, which so far have been rarely analyzed). This article presents a study to examine and explain the magnitude of strains developed in loading and unloading curves of PBP to predict the ratio of compression to unloading strain (εc/εu) and Su from unloading curves, for which open field experimentation is conducted on saturated clay deposits with a plasticity index of 10 to 16 %. The results of εc/εu and Su that were determined from the undrained PBP tests were compared with anisotropically consolidated undrained triaxial compression tests, which showed reasonable agreement. Correlations are proposed for net limit pressure versus εc/εu and Su from PBP, which offer a new approach to quantifying εu and Su by solely performing compression curves. The proposed correlations are validated by performing PBP tests at two separate sites and are further supported by comparison with the pressuremeter curves of previous studies. The variation in experimental versus predicted values for two separate sites (using the proposed correlation) is within ±10 % for a confidence interval of 95 %.

Deformation capacity of 400 N/mm2 class structural steel under extremely large strains

To provide qualitative database for further studies regarding the evaluation of the cyclic deformation capacities of 400 N/mm2 class structural steel up to the maximum strength as well as the complete fracture, strain-based cyclic loading tests were performed in the low and extremely low-cycle fatigue regimes. Thirty-nine specimens were employed and tested with strain amplitudes in the range from ±2% to ±12%. By using three different specimen configurations made from three different lots of steel materials, and by performing axial cyclic tests (starting with tensile and compressive loads), the influences of different lots, specimen configurations, and different initial loading directions on the strain-life curve could be examined. The experimental results indicated that cyclic hardening behaviors of all specimens occurred in the first several cycles, while specimens tested with smaller strains (3% or below) stabilized until failure. However, specimens fractured in a ductile manner without achieving stabilization when they were subjected to large strain tests. The strain-life curve (up to failure) exhibited a linear relationship with strain amplitudes up to 10%. At larger strain amplitudes, the cyclic deformation capacity of the steel material reached its peak and subsequently became nonlinear. Nevertheless, the strain-life curves up to peak cyclic stress of all specimens show a continuous linear relationship with strain amplitudes up to 12%.

Wave propagation in glass fibre-reinforced polymer (GFRP) bars subjected to progressive damage—Experimental and numerical results

Glass fibre reinforced polymer (GFRP) is a material of increasing interest in civil engineering applications. It is used as internal reinforcement for concrete structures (especially in extremely corrosive environments), as well as structural profiles, plates, and gratings. However, estimating the life of GFRP structures represents a challenge for the construction industry. To address this challenge, a numerical model of elastic wave propagation in GFRP bars is presented in this paper so that it can be used to reduce the number of physical testing required to estimate the degradation of GFRP bars in the field.The proposed numerical model is designed to assist the application of ultrasonic non-destructive testing (NDT) techniques and develop a framework for the evaluation of progressive damage of GFRP bars due to a highly alkaline environment. The proposed methodology consists of: (i) development and calibration of a numerical model of elastic wave propagation in GFRP bars in Abaqus, (ii) simulation of deterioration of the bars, and (iii) comparison of experimental, large and low strain tests (shear test and ultrasonic evaluation) with results of numerical simulations.The results show that the model (low strain properties) correctly captures the deterioration rates seen in the shear strength test (large strains). The model is used to study ultrasonic features and demonstrates that low strain measurements (e.g. wave dispersion, wave amplitude) can be used to estimate the effect of progressive damage on large strain properties in GFRP bars, which can result in a decreased number of required destructive tests.

Investigation of 1D sand compression response using enhanced compressibility model

1D sand compression response to ko-loading experiences volume contraction from low to high effective stress regimes. Previous study suggested compressibility model with physically correct asymptotic void ratios at low and high stress levels and examined only for both remolded clays and natural clays. This study extends the validity of Enhanced Terzaghi model for different sand types complied from 1D compression data. The model involved with four parameters can adequately fit 1D sand compression data for a wide stress range. The low stress obtained from fitting parameters helps to identify the initial fabric conditions. In addition, strong correlation between compressibility and the void ratio at low stress facilitates determination of self-consistent fitting parameters. The computed tangent constrained modulus can capture monotonic stiffening effect induced by an increase in effective stress. The magnitude of tangent stiffness during large strain test should not be associated with small strain stiffness values. The use of a single continuous function to capture 1D stress-strain sand response to ko-loading can improve numerical efficiency and systematically quantify the yield stress instead of ad hoc methods.

Small and large strain rheology of gluten and gluten-starch doughs containing wheat bran dietary fiber.

The small and large strain rheology of gluten (G) and gluten-starch (G + S) doughs containing wheat bran dietary fiber (WBDF) were investigated. At the small strain stage, i.e. frequency and strain sweep tests, the doughs containing high WBDF concentration are more vulnerable and unstable, as indicated by the lower dough linear viscoelastic strain limit as well as the higher slope of elastic modulus. However, the elastic nature of doughs remarkably increased upon WBDF addition, indicating the reinforcement of the dough mechanical strength, which is also confirmed by the large strain test wherein the maximum strain significantly decreased from 4.37 to 1.82 for the G system and from 12.09 to 2.72 for the G + S system. The creep recovery test showed that WBDF induced the reduction in the strain of the doughs at a fixed stress, which may be related to the enhanced strain hardening capacity. The addition of WBDF resulted in more brittle and unstable doughs with undesirable higher mechanical strength. The presence of starch greatly weakened the dough strength and led to inferior resistance to both small and large deformations. These findings confirmed the impairment of dough viscoelasticity upon addition of WBDF. © 2019 Society of Chemical Industry.

Large Strain and Small-Scale Biaxial Testing of Sheet Metals

Small-scale and multi-axial testing of sheet metals, particularly of lightweight alloys and advanced steels are becoming important as these materials exhibit forming behavior sensitive to their unique microstructural features and strain paths. As an alternative to large-scale standard tests, in this paper we introduce a novel biaxial tensile test apparatus utilizing miniature cruciform samples. The compact and portable apparatus includes a custom-built optical microscope and high-resolution digital image correlation (DIC) equipment for in-plane and in-situ strain measurements at the microstructure scale. The small strain and premature fracture problems common to the cruciform tests are solved by optimizing the sample design and by meticulously controlling the manufacturing steps and surface finish. Strain analyses reveal a key mechanism responsible for large strains and fracture at the center. This mechanism suppresses the local neck formation and allows uniform deformation under equibiaxial conditions until fracture. When normalized with the strain hardening exponent of the sample material (Al 6061-T6), the effective strain value before fracture, $$ \overline{\varepsilon}/n \sim 3 $$ , surpass the reported values for similar materials tested by cruciform and standard methods.

A Shear-Tension Specimen for Large Strain Testing

A new shear-tension specimen (STS) is designed, evaluated and tested quasi-statically and dynamically. The specimen consists of a long cylinder having an inclined gauge section created by two diametrically opposed semi-circular slots which are machined at 45° with respect to the longitudinal axis. The geometry imposes stress condition within the gauge section which correspond to a Lode parameter of ~ −0.5, between pure shear (0) and uniaxial tension (−1). It thus provides a wider span of loading conditions for a material. A thorough numerical study reveals that the stresses and strains within the gauge are rather uniform, and the average Mises stress and plastic strain on the mid-section of the gauge represent the material true stress–strain characteristics. The data reduction technique to determine the stresses and strains is presented. Quasi-static and dynamic tests at strain rate of 104 1/s were carried out on specimens made of 1020 cold-rolled steel. No necking or softening was observed with this specimen, and the fracture location was always well within the gauge. The obtained stress–strain curves and ductility were validated numerically. The STS is a new specimen to study the combined influence of tension and shear on the mechanical characteristics of a material.

Modification of the Shear-Compression Specimen for Large Strain Testing

A modified shear-compression specimen (SCS), for large strain testing over a wide range of strain rates is presented. The original SCS design includes two rectangular slots that are machined at 45° with respect to the longitudinal axis. The modification consists of creating two diametrically opposed semi-circular slots. The new “circular” specimen is first thoroughly investigated numerically under quasi-static and dynamic loading using an elasto-plastic material model. The results of the comparison between the two-slot designs confirm the feasibility of the new specimen for larger strain testing and indicates its advantages over the rectangular slot design: larger strain range characterization, failure and fracture within the gauge, and constant Lode parameter during plastic deformation. Both types of SCS as well as cylindrical specimens are used to characterize the flow behavior of steel 1020, in the quasi-static and dynamic regimes using a split Hopkinson pressure bar. Dog-bone specimens are also tested quasi-statically in tension. A very good agreement is achieved for the results of all specimens in both the quasi-static and dynamic regimes. The numerical validation procedure shows that the flow stress of 1020 steel obtained with the new SCS is ~3 % lower in the quasi-static regime, and 8 % lower in the dynamic regime with respect to the flow stress of the rectangular SCS. This difference is attributed to effect of the third invariant of the stress deviator (i.e., Lode parameter), which is considerably lower in the new SCS design.

用于船舶结构监测的大量程光纤布拉格光栅应变传感器

Fiber Bragg Grating(FBG)sensor with a stickup plane structure can not test the strain precisely in ship structure health monitoring due to its small measuring range.For overcoming this problem,this paper designs a composite structure stickup FBG sensor composed of an annular plane spring and a slab on the basis of stainless steel.This kind of stickup FBG sensor can convert the large strain of composite structure into a small strain of FBG by the annular plane spring.By decreasing the strain coupling coefficient between FBG and tested structure,large-scale strain test is implemented.The sensing principle of the composite structure is analyzed and the stress and strain distribution of the stickup FBG sensor are simulated through finite element method.The simulation result demonstrates the feasibility of this structure in a large strain test.Finally,a loading experiment are performed on a special steel sample.The experiment result shows that this structure has a measuring range more than 20 000μeand good linearity.In addition,the correlation coefficient is up to 0.99.As a conclusion,the sensor is convenient for setting up because of the small volume,and can resolve the problem of large strain test in ship structure health monitoring with good performance.

Reliability of GDS-RCA Resonant Column on Routine Experimentation

The shear modulus and damping ratio of soil are important factors for soil layer seismic response analysis, people have done a lot of research. Currently, the method to measure soil shear modulus and damping ratio have bending element test method, resonant column test, dynamic triaxial test and so on. This article describes the British GDS company developed a new resonant column GDS-RCA's main features, technical indicators and working principle, compared the IEM original GZ-1 resonant column test results with GDS-RCA resonant column test results, the compared results are as follows: both damping ratio results in somewhat different, but in 10-6-10-4low strain shear modulus ratio between the range of test results are consistent, GDS-RCA resonant column testing machine can by low-frequency torsional mode, expand the soil strain measurement extended to 10-6-10-2, and the small strain to large strain test results are in good connection.

Combined Resonant Column and Cyclic Triaxial Tests for Measuring Undrained Shear Modulus Reduction of Sand With Plastic Fines

This paper investigates the undrained shear stiffness of sand–bentonite specimens (with 0 %, 3 %, and 5 % bentonite by dry mass of the sand) prepared at the same skeleton void ratio (Drsk = 35 % to 40 %) using a dry pluviation technique. The experimental program consisted of (1) small strain tests using a resonant column apparatus and (2) large strain tests using a cyclic triaxial apparatus. The resonant column tests were performed at three confining stress levels (50, 100, and 193 kPa) under drained and undrained conditions. A comparison of the shear modulus reduction with shear strains for both drained and undrained conditions is presented; the effects of changes in effective stresses and the rate of modulus reduction as a function of the effective stress are discussed to describe the discrepancy between the two sets of data. The results show a marginal decrease in Gmax for specimens with bentonite, which is attributed to the presence of bentonite at the sand grain contacts. However, the presence of bentonite increases the linear elastic threshold, particularly in the case of undrained tests, in which a noticeable delay in excess pore pressure generation was measured. The strain level required in order to initiate excess pore pressure generation increased with increasing bentonite content. A similar trend was noted in cyclic triaxial tests, in which, for a given strain, specimens with bentonite generated lower excess pressure than sand specimens tested under similar conditions. Finally, a combined normalized G/Gmax curve from both tests is presented for specimens with 0 %, 3 %, and 5 % bentonite at 100 kPa.

Relating Large Amplitude Oscillatory Shear and Food Behavior: Correlation of Nonlinear Viscoelastic, Rheological, Sensory and Oral Processing Behavior of Whey Protein Isolate/κ‐Carrageenan Gels

AbstractCreating desirable food textures begins with a fundamental understanding of texture, which involves measuring mechanical properties of the food product. Large strain mechanical properties have been correlated with sensory and oral processing characteristics; however, most large strain testing in food research involves determination of fracture properties rather than examination of nonlinear viscoelastic behavior. Relationships between nonlinear viscoelastic behavior and food texture were determined by measuring and correlating nonlinear viscoelastic properties of several whey protein isolate/κ‐carrageenan gels to sensory, oral processing and large strain rheological characteristics. Nonlinear viscoelastic properties correlated (R2 > 0.5, P < 0.05) to sensory, oral processing and large strain rheological behaviors. Sensory correlations included aspects evaluated after several chews as well as first bite aspects. Oral processing correlations generally involved jaw movement terms rather than electromyographical data. Understanding the nonlinear viscoelastic properties of food allows a better understanding of food structure and deformation mechanism and how that structure impacts food texture.Practical ApplicationsThis work demonstrates the applicability of large amplitude oscillatory shear (LAOS) testing in food science. The LAOS measurement and analysis method may be applied to foods with a wide range of structure and texture, allowing measurements of nonlinear viscoelastic behavior in materials that cannot be tested under current methodology. In addition, LAOS measurements can indicate structural aspects of the material, and correlations between structure and texture may be made from this information.

Nondestructive Assessment of Axial Load–Deflection Behavior of Drilled Shafts for a Suspension Bridge

The new Rio Cuarto Bridge, currently under construction in the Province of Cordoba, Argentina, consists of a 110-m long, cable-stayed main span with a prestressed concrete deck, steel pylons, and two 50-m–long side spans founded on groups of drilled shafts. The construction method, structural configuration of the superstructure, and post-tensioning sequence of the cables required a detailed characterization of the axial load behavior of the drilled shafts, both for the temporary support shafts and the foundation piers. Small-strain and working load level predictions were made during design, on the basis of conventional site investigation information and in situ geophysical testing. A series of nondestructive evaluations, coupled with nonlinear extrapolations calibrated to represent the measured small-strain range, were carried out in lieu of conventional verification of design predictions by means of more cumbersome large-strain testing. The testing program consisted on monitoring accelerations generated at the top of the shaft as a result of a small amplitude dynamic load measured by means of a dynamic force transducer. A nonlinear numerical model was then calibrated so as to reproduce the initial stiffness measured during the small-strain testing program to extrapolate the load-deflection curve into the service load range and thus define load-deflection curves of the shafts at each pier location up to service load levels. To obtain an experimental validation of the approach at the site, a conventional static load test, carried up to the service load level, was performed on a main pier shaft. Results showed a reasonable agreement between the nondestructive evaluation with nonlinear extrapolation, large-strain measurements, and design predictions for the main pier shafts, whereas some differences were observed between the design predictions and small-strain measurements at other locations, primarily as a result of as-built conditions unforeseen in the original design. Thus, the nondestructive testing program was instrumental in the verification of the as-built behavior of the shafts and allowed the development of load-deflection curves for the drilled shafts that accurately represented the behavior up to the service load level.

COMPOSITION, PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF FRESH BIGEYE SNAPPER FISH (PRIACANTHUS HAMRUR) MINCE

ABSTRACT Composition and properties of fresh bigeye snapper fish (Priacanthus hamrur) mince has been investigated. The protein content of fish mince was 16.71 g/100 g mince. Amino acid analysis revealed high proportion of glutamic acid, alanine, lysine and leucine. Fatty acid profile indicated high proportion of eicosa pentaenoic acid and decosa hexaenoic acid content. Gel filtration profile of total proteins from fresh bigeye fish mince revealed a major peak (high molecular weight component) and a few minor peaks, which was further confirmed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis pattern. The differential scanning calorimetry profile of fresh bigeye fish mince revealed transitions at 38.35, 47.72 and 63.02C indicating denaturation temperature of different protein fractions. The gel-forming ability of fresh bigeye fish mince was evaluated by both small strain and large strain tests. The flow behavior of total protein solution from fresh bigeye fish mince as a function of protein concentration and temperature showed pseudoplastic behavior. PRACTICAL APPLICATIONS The properties of fish mince including amino acid and fatty acid profile are critical in deciding the nature of processed products to be prepared. Because of lower catch of bigeye snapper in formerly, this fish was not commonly available and hence, it has been regarded as a nonconventional marine fishery resource. Recently, bigeye snapper has assumed significance as an important species in the commercial landings. In the present investigation, composition, thermal and rheological properties of fresh bigeye snapper mince have been assessed. A high proportion of omega 3 fatty acids shows the nutritional importance of this fish whereas its gel-forming ability shows the potential to be utilized as raw material in the surimi industry. Establishing the thermal denaturation profile, measurement of dynamic viscoelstic behavior and assessing the flow behavior of proteins from bigeye snapper will aid in the appropriate processing and design in formulating mince-based products.

Purification and characterisation of transglutaminase from four fish species: Effect of added transglutaminase on the viscoelastic behaviour of fish mince

The transglutaminase (TGase) enzyme from four different fish species, namely bigeye snapper, Indian oil sardine, tilapia and common carp have been isolated and characterised. The specific activity of the enzyme was higher in tilapia followed by oil sardine, common carp and bigeye snapper. The molecular weight of pure TGase was found to be in the range of 73–95kD for four different fish species. The temperature optima for maximum activity of TGase varied amongst four species studied. The effect of activator (calcium chloride) and inhibitors (ethylenediaminetetraacetic acid (EDTA), ammonium chloride and free lysine–hydrochloride) at different concentrations on the TGase enzyme activity have been evaluated. The addition of isolated TGase to fish mince from Cynoglossus sp. was attempted in order to evaluate the setting and gelling ability. The setting and gelling ability of fish mince in presence of TGase improved considerably as revealed by small strain and large strain test.

Microstructural characterisation of deformation behaviour of nickel base superalloy IN625

Simple compression and microscopy techniques were employed to characterise the microstructural origin of the deformation behaviour of nickel base superalloy IN625 during large strain testing. The alloy exhibited a four-stage strain hardening response similar to that previously reported for low stacking fault energy face centred cubic alloys. At strains lower than about −0·06 (stage A), a falling regime of the hardening rate was observed. This stage was followed by a second stage (stage B) of slow increasing hardening rate, which was found to be coincident with the formation of Lomer–Cottrell locks. The second falling regime of strain hardening (stage C) was seen in the strain range of −0·25 to −0·65. The occurrence of this stage was attributed to the increasing ease of dislocation cross-slip with increasing strain and consequently to the decreasing Lomer–Cottrell lock efficiency in hindering dislocation movement. Beyond a strain of −0·65, a final slightly constant hardening regime (stage D) was developed. The initiation of this stage was concurrent with the onset of deformation twinning in the microstructure.

Ultrasonic characterization of exhumed cast iron water pipes

Cast iron pipe has been used as a water distribution technology in North America since the early nineteenth century. The first cast iron pipes were made of grey cast iron which was succeeded by ductile iron as a pipe material in the 1940s. These different iron alloys have significantly different microstructures which give rise to distinct mechanical properties. Insight into the non destructive structural condition assessment of aging pipes can be advantageous in developing mitigation strategies for pipe failures. This paper examines the relationship between the small-strain and large-strain properties of exhumed cast iron water pipes. Nondestructive and destructive testing programs were performed on eight pipes varying in age from 40 to 130 years. The experimental program included microstructure evaluation and ultrasonic, tensile, and flexural testing. New applications of frequency domain analysis techniques including Fourier and wavelet transforms of ultrasonic pulse velocity measurements are presented. A low correlation between wave propagation and large-strain measurements was observed. However, the wave velocities were consistently different between ductile and grey cast iron pipes (14% to 18% difference); the ductile iron pipes showed the smaller variation in wave velocities. Thus, the variation of elastic properties for ductile iron was not enough to define a linear correlation because all the measurements were practically concentrated in single cluster of points. The cross-sectional areas of the specimens tested varied as a result of minor manufacturing defects and levels of corrosion. These variations affect the large strain testing results; but, surface defects have limited effect on wave velocities and may also contribute to the low correlations observed. Lamb waves are typically not considered in the evaluation of ultrasonic pulse velocity. However, Lamb waves were found to contribute significantly to the frequency content of the ultrasonic signals possibly resulting in the poor correlations observed. Therefore, correlations between wave velocities and large strain properties obtained using specimens manufactured in the laboratory must be used with caution in the condition assessment of aged water pipes especially for grey cast iron pipes.

Characterization and utilization of noisy displacement signals from simple shear device using linear and kernel regression methods

Small strain testing of dynamic soil properties such as threshold strains, γ tv , are often conducted using specialized devices such as dual-specimen simple-shear, as devices configured for large strain testing produce noisy signals in the small strain range. Working with a simple shear device originally developed for large-strain testing, we extend its low-strain capabilities by characterizing noisy signals and utilizing several statistical methods to extract meaningful responses in the small strain range. We utilize linear regression of a transformed variable to estimate the cyclic shear strain from a noisy signal and the confidence interval on its amplitude. We utilize Kernel regression with the Nadaraya–Watson estimator and a Gaussian kernel to evaluate vertical strain response. A practical utilization of these techniques is illustrated by evaluating threshold shear strains for volume change with a procedure that takes into account uncertainties in the measured shear and vertical strains.