Apparent Strain Research Articles

Parametric investigation of the effects of load level on fatigue crack growth in trabecular bone based on artificial neural network computation.

This study reports the development of an artificial neural network computation model to predict the accumulation of crack density and crack length in cancellous bone under a cyclic load. The model was then applied to conduct a parametric investigation into the effects of load level on fatigue crack accumulation in cancellous bone. The method was built in three steps: (1) conducting finite element simulations to predict fatigue growth of different three-dimensional micro-computed tomography cancellous bone specimens considering input combinations based on a factorial experimental design; (2) performing a training stage of an artificial neural network based on the results of step 1; and (3) applying the trained artificial neural network to rapidly predict the crack density and the crack length growth for cancellous bone under a cyclic loading for a given applied apparent strain, cycle frequency, bone volume fraction, bone density and apparent elastic modulus.

Flow properties of surfactant solutions of rod-like micelles passing through a small slit

Pressure drops in flows through a small slit were experimentally measured at constant flow rates to investigate flows with an abrupt contraction and expansion. The flow properties of water, 50 wt% glycerol solution, and two types of surfactant solutions (Lipoquad and Lipothoquad) with a counterion (NaSal) were examined. The slit heights used were 480 µm, 222 µm, and 129 µm, with estimated hydraulic diameters of 938 µm, 439 µm, and 256 µm, respectively. Viscosity was measured using a capillary-type viscosity meter. Water and the 50 wt% glycerol solution exhibited Newtonian viscosity, with the viscosity of the glycerol solution being 10 times that of water. By contrast, the surfactant solutions, which contained rod-like micelles, exhibited non-Newtonian viscosity. A power law model was therefore applied for the relationship between shear viscosity and shear rate on the wall. The observed flow properties of water (and the 50 wt% glycerol solution) and the numerical predictions of the Navier–Stokes equations were found to agree to within the experimental errors. In plots of the dimensionless pressure drop against the generalized Reynolds number, however, anomalous flow properties of the surfactant solutions were observed. The pressure drops of Lipoquad/NaSal agreed with those of water (and the 50 wt% glycerol solution) at low apparent strain rate (Reynolds number) but were larger at high apparent strain rate (Reynolds number). Furthermore, the pressure drops of Lipothoquad/NaSal were greater than those of water in the investigated range of the generalized Reynolds number. To examine these experimental results further, flows in a planar channel with an abrupt contraction and expansion were observed using a polarization measurement system based on a high-speed polarization camera. In contrast to polymer solutions (in which polymer chains were oriented along the flow direction), the phase difference for Lipoquad/NaSal before and in the slit region was high in regions with a strong elongational component. In addition, it was high along the centerline after the slit region. These results also differ from those of simple shear flows. Furthermore, the phase difference of Lipothoquad/NaSal was very unstable. In addition, the relationship between the resultant pressure drop and the measured phase differences was investigated, and a dependence was found on the apparent strain rate (Weissenberg number).

Size Effect on Mechanical Properties of Rock-Like Materials with Three Joints

In order to study the size effect, failure mode and damage evolution process of rock-like materials with three joints, two rock-like materials with different sizes of joints were prepared for uniaxial compression tests. The digital image correlation technique was used to record the change characteristics of the apparent strain field, and an acoustic emission device was applied to record the damage process. The results show that the peak compressive strength of samples with the same joint inclination decreases with the increase of size. The peak compressive strength of samples decreases obviously when the joint inclination ranges from 0°–45° and 75°–90°. When the joint inclination ranges from 45° to 75°, the peak compressive strength of samples decreases insignificantly. With the increase of joint inclination, the peak compressive strength of the sample decreases gradually. It reaches the minimum when the joint inclination angle is 60°, and then the peak compressive strength steadily increased. It is prone to failure when the joint inclination is 60°. According to the crack propagation model, the failure modes of jointed samples can be divided into five failure modes: tension failure, airfoil tension failure, tension-shear mixed failure, shear failure and integral splitting failure. According to the damage curve, the damage evolution process can be divided into inverted L type, spoon type, S type and straight hook type. Large size samples and samples with joint inclination of 0°, 90° and 60° are prone to brittle failure and step damage.

Indentation creep vs. indentation relaxation: A matter of strain rate definition?

An extensive study of the different methods able to measure material creep properties in indentation is proposed. A systematic comparison of the fast creep, long-term creep, constant strain rate and long-term relaxation tests is performed on amorphous selenium. Even though measured apparent activation energy and strain rate sensitivities are very similar for all tests, a discrepancy is highlighted between the creep/constant strain rate tests and the relaxation tests. This effect seems to be related to the strain rate definition which should be a function of the strain rate sensitivity m. In this paper, it is proposed to use a representative strain rate ϵ̇r as proposed by Kermouche et al. (2008). An excellent agreement is found between all the methods, including uniaxial compression when expressing the creep behavior as a function of representative stress and strain rate.

Effect of titanium in aluminium matrix on densification and forming limit of P/M composites during upsetting process

The present work investigates the densification and forming limit of sintered porous aluminium–titanium preforms for various relative densities and titanium particles. The compacts of 1 aspect ratio with 2–6% of titanium contents in aluminium matrix for various relative densities were prepared through powder metallurgy route by applying suitable powder forming pressures. A sequence of the cold upsetting test has been carried out using 0.5 MN capacity of hydraulic press machine at 0.1 s−1 strain rate. The relation between true axial strain and preforms relative density was plotted, and the influence of titanium and relative density on the densification curve was investigated at various compaction pressures. The specimen properties like apparent strain hardening exponent (na) and apparent strength coefficient (Ka) was determined through stepwise incremental deformation tests. The critical transition density (CTD) vide forming limit diagram was determined from the plot of na and Ka concerning the preforms relative density, and it was found to be 85.9%, 87.7% and 88% for 2%, 4% and 6% of titanium in the aluminium matrix. The CTD values of porous aluminium–titanium preforms were compared with those of the previous work of porous aluminium–copper preforms under the same compositions. Also, the average grain size of the components was determined and it is observed that 2% of titanium contains a larger grain size compared to other compositions. Hence, a higher forming limit was obtained in 2% of titanium reinforced with aluminium matrix.

Effect of initial dislocation density on hydrogen accumulation behavior in martensitic steel

We investigated hydrogen accumulation behavior of martensite structures with different initial dislocation densities. The hydrogen micro-print technique and microstructure observation revealed that the higher initial dislocation density facilitated hydrogen accumulation around prior austenite grain boundaries during deformation within the apparent elastic strain regime. In contrast, once deformation was applied to the plastic strain regime, hydrogen accumulation behavior did not change with initial dislocation density. Based on the obtained results, we concluded that transportation of hydrogen by dislocation motion played an important role on hydrogen accumulation around prior austenite grain boundaries.

Influence of High Water Pressure on Static and Dynamic Compressive Strength of Concrete

In this paper, an experimental study was conducted on the influence of water pressure on concrete strength. Specimens were put in a self‐designed device, applying 0–4 MPa water pressure on concrete, and then taken out for both static and dynamic compressive tests. Results showed that high water pressure caused inevitable damage to concrete, leading to 13.4% reduction in strength under 4 MPa water pressure. Specimens with lower strength grade were damaged more severely while under the same water pressure. Also, as water pressure increased, the moisture content of concrete grew linearly, and the trend for specimens with higher compressive strength was slower. A correlation was established between the water content increment and the reduction rate of strength. Moreover, the dynamic compressive strength decreased as water pressure increased but still higher than the static strength, illustrating an apparent strain rate effect. Meanwhile, water pressure and moisture content increment barely had any influence upon DIF within the testing conditions. Furthermore, equations for calculating both static and dynamic reduction rates of strength were built, based either on water pressure or on moisture content increment caused by that. Equations for strength prediction were also provided.

Hierarchically organized materials with ordered mesopores: adsorption isotherm and adsorption-induced deformation from small-angle scattering.

In situ small angle scattering is used to study the pore filling mechanism and the adsorption induced deformation of a silica sample with hierarchical porosity upon water adsorption. The high structural order of the cylindrical mesopores on a 2D hexagonal lattice allows obtaining adsorption induced strains from the shift of the corresponding Bragg peaks measured by in situ small-angle X-ray scattering (SAXS). However, apparent strains due to scattering contrast induced changes of the Bragg peak shapes emerge in SAXS. In contrast, small-angle neutron scattering (SANS) allows determining the real adsorption induced strains by employing a H2O/D2O adsorbate with net coherent scattering length density of zero. This allows separating the apparent strains from the real strains experimentally and comparing them with strains obtained from model calculations of the SAXS intensity. It is shown that the apparent strains cannot be described at all by a simple mesopore model of film growth and capillary condensation. A hierarchical model taking the scattering of the micropores and the outer surface of the mesoporous struts in the hierarchically porous sample properly into account, together with a modified mesopore filling mechanism based on a corona model, leads to satisfactory description of both, the adsorption isotherm and the measured apparent strains as derived by SAXS.

Influence of different culture conditions on exopolysaccharide production by indigenous lactic acid bacteria isolated from pickles.

The objective of this study was to assess the effects of some culture conditions [temperature (20, 30, 37°C), incubation time (48, 72, 120h), pH (5.0, 6.0, 7.0), NaCl concentration (0, 3, 6%), carbon (glucose, fructose, lactose), nitrogen (sodium nitrate, ammonium sulfate, bacto-peptone), and mineral sources (calcium carbonate, ferric chloride)] on the exopolysaccharide (EPS) production by lactic acid bacteria (LAB) strains (belonging to Lactobacillus (L.) plantarum, L. namurensis, and Pediococcus (P.) ethanolidurans species) isolated from naturally fermented pickles. The maximum EPS production was determined at 30°C and pH 6.0. The highest amount of EPS was obtained after 120h of incubation, with glucose as carbon source, bacto-peptone as nitrogen source and calcium carbonate as mineral source for most of the tested strains. The EPS formation was not stimulated by NaCl, indicating that EPS formation of the tested strains was not a stress response. L. plantarum MF460 produced the highest amount of EPS at 30°C after 48h of incubation, which was 515.48mg/L. One of the most pronounced results of this study was that the EPS production of L. plantarum MF556 strain was increased up to 512.81mg/L with the addition of calcium carbonate to MRS medium. The effect of different culture conditions, particularly of incubation time, carbon, nitrogen, and mineral sources, on the EPS production often vary depending on the strain. Therefore, these apparent strain specific results demonstrated that the optimum culture conditions for the enhanced EPS production should be specifically determined for each LAB strain.

The Eye of a Needle: Temporary Prison Leave in Ukraine

Although temporary prison leave humanises custodial punishment, offsets its negative effects, and prepares prisoners for (re)integration into wider society, its use proves to be controversial and uneven across jurisdictions. Since the collapse of the USSR, the former Soviet countries have been pursuing different criminal justice policies, liberalising some penal practices whilst retaining many punitive Soviet legacies. Through analysis of the legal provisions regulating temporary prison leave and official statistics in Ukraine, I demonstrate the apparent strain between the official policies and practice. Whilst legally available, temporary leave for prisoners in closed prisons is almost never granted in this Eastern European country. I argue that for Ukraine to reconcile the official rhetoric of rehabilitation and social reintegration of offenders and actual implementation of penal policies, the country must reverse the underlying requirements governing temporary prison leave and expand its use.

Assessing the Use of Wing Morphometrics to Identify Fall Armyworm (Lepidoptera: Noctuidae) Host Strains in Field Collections.

The fall armyworm (Spodoptera frugiperda) (J. E. Smith) (Lepidoptera: Noctuidae), a major agricultural pest in the Western Hemisphere, has recently become established in Africa and Asia. This highly polyphagous species has potential to economically harm multiple crops. Contributing to this host range are two fall armyworm populations historically called 'host strains' that differ in host specificity. Understanding behaviors of the two strains is crucial to effective management of this pest. A major difficulty in such studies is that strains have long been considered morphologically indistinguishable, with molecular markers the only reliable means of identification. However, studies of fall armyworm in Colombia reported strain differences in wing morphology sufficiently large to potentially provide a more economical alternative method to determine strain. This study tested whether a similar phenotypic difference was present in Florida populations using geometric morphometric analysis of 15 anatomical landmarks on forewings of 182 specimens from three habitats associated with different host plants. Principle component and linear discriminant analyses identified significant differences in wing size and shape in comparison of strains from different habitats, but not between strains within the same habitat. Data indicate that apparent strain distinctions in wing phenotype are most likely a secondary consequence of differences in developmental growth patterns on different host plants combined with strain-biased host choice. Furthermore, Florida specimens showed much larger phenotypic overlap than observed for strains from Colombia. Together these findings suggest that wing morphology is probably not a reliable indicator of strain identity in field populations where different host plants are available.

Cyclic test on a precast reinforced concrete column-to-foundation grouted duct connection

A full-scale specimen of a column-to-foundation grouted duct connection suited for buildings and industrial structures is tested in cyclic bending combined with axial compression. The positioning of the steel ducts along the sides of the column cross-section allows for using traditional reinforcement cages for the column, with longitudinal bars at both mid-side and corners of the cross-section. Splice length and amount of transverse reinforcement along the splice are defined based on Eurocode 2 provisions for laps of reinforcing bars. A total of 19 loading cycles are carried out, achieving a drift of 5.3% in correspondence of a degradation of 15% of the peak resistance. The shear slip measured at the column-foundation interface results to be smaller than 5% of the deflection. Conversely, to predict accurately the test results, the slip of the projecting bars within their ducts cannot be neglected. It is proposed to take account of this slip by introducing an apparent strain. For the tested specimen, the apparent strain turns out to be equal to the yield strain of the reinforcement. A comparison with a monotonic bending test, previously conducted on the same connection, shows a strongly smaller deformability when the loading protocol is cyclic. Hysteretic energy and drift ductility for the proposed connection are close to those concerning a cast-in-place specimen of comparable capacity, which was described in a recent paper. The test results show an over-strength of 1.4 and a gain in ductility of 1.8 compared with the design values of bending resistance and curvature ductility computed for the cross-section at the column-foundation interface.

Modulus reductions of dam embankment materials based on downhole array time series

A database of three-component acceleration time series recorded at downhole arrays in earthen dam cores was published by the Japan Commission on Large Dams. This study reviews the acceleration time series in nine earthfill and rockfill dams in Japan. The apparent shear wave velocities between downhole sensors in each dam during strong shakes are determined by calculating the wave travel time between the recorded time series. Transient shear strains are calculated from the differences in the displacement time series between sensors through the double integration of filtered acceleration time series. The modulus reduction curves of the in situ core materials are constructed by combining the apparent shear wave velocities and shear strains. The modulus reduction data are then compared with empirical models. Observations show considerable uncertainties and dam-dependent characteristics in the extracted in situ shear modulus. Accordingly, this study proposes a methodology to update the empirical modulus reduction model for dam core materials on the basis of observed data on downhole time series.

Relaxation Behavior and Nonlinear Surface Rheology of PEO-PPO-PEO Triblock Copolymers at the Air-Water Interface.

Surface dilatational viscoelasticity of adsorbed layers of pluronics triblock copolymers at the air-water interface was measured using the oscillating barrier technique. The effect of molecular architecture and concentration on surface viscoelasticity was explored for two different types of pluronics with different degrees of hydrophobicity, Pluronic F-108 (Mw ≈ 14 600 g/mol) and Pluronic P-123 (Mw ≈ 5800 g/mol), the former exhibiting a larger hydrophilic to hydrophobic block length ratio. Frequency sweeps in the linear regime suggested that interfacial films of F-108 have higher surface limiting elasticity and larger in-plane and out-of-plane relaxation times at the same bulk concentration (the former possibly related to in-plane microstructure rearrangements, the latter to surface/bulk diffusion). Increasing the bulk concentration of pluronics from 1 to 100 μM led to a decrease in both in- and out-of-plane relaxation times. Large amplitude oscillatory dilatation (LAOD) tests were performed to capture nonlinear behavior of these interfacial films by means of elastic and viscous Lissajous plots. Nonlinearities in elastic responses were quantified through calculation of the strain-stiffening indices in extension SE and compression SC. Both pluronics exhibited strain softening in extension. In compression, P-123 showed strain-hardening and F-108 displayed a relatively linear response. Apparent strain hardening in extension was observed for the P-123 adsorbed film, at high strain, at a bulk concentration of 100 μM. However, at these strains, the response was dominated by the viscous contribution and calculation of strain rate-thickening factors in extension and compression showed that the overall response was strain rate-thinning in extension and strain rate-thickening in compression.

A study on the nonlinear elastic behavior of ballistic gelatin using a rotational rheometer

The present work was focused on the study of large elastic behavior and constitutive modeling of ballistic gelatin. The simple shear tests were conducted using a rotational rheometer. It is observed that the mechanical parameters of the material should be analyzed directly by the data of rotational angle and torque measured by the rheometer but not the apparent shear stress and strain data provided by the rheometer directly. A hyperelastic constitutive model, a 2-term reduced polynomial strain energy potential, was adopted to describe the nonlinear stress-strain relationship. The material parameters were identified and the dependency of the parameters on the temperature was analyzed. It’s found that the modulus at small deformation decreases with increasing temperature following an approximately linear relationship; while, the modulus at large deformation showed a process of first increasing and then decreasing with increasing temperature.

Rheological properties of tomato ketchup

The objective of this paper was to determine the rheological properties especially shear stress and apparent viscosity vs. shear strain rate, and density of commercially available but also homemade tomato ketchup. The effect of tomato content of density and apparent viscosity of tomato ketchup was also described. Shear stress and apparent viscosity were observed in shear strain rates range from 0.1 s-1 up to 68 s-1. All measurements were carried out at a constant temperature of 22 °C. Experimental results were modeled using a power-law (also known as Ostwald-de Waele) model (R2 ranged from 0.9508 up to 0.9991). The flow behaviour of all measured tomato ketchup samples exhibited non-Newtonian pseudoplastic (shear thinning) behavior where the flow index (n) showed values between 0 and 1. Flow index (n) and consistency coefficient (K) can be used especially in numerical simulation of the flow behaviour of pseudoplastic (shear thinning) liquids.

Analysis of the transverse compressive behavior of Kevlar fibers using microscopic scale approach

During the ballistic impact process of fabrics, yarns are locally subjected to both longitudinal tensile and transverse compressive loading. This paper presents a microscopic numerical investigation of the transverse compressive behavior of a single and bulk aramid fibers. Interactions with friction between single fibers in a yarn have been taken into account. Numerical calculations were performed in the case of a transverse compression using the assumption of plane strain and validated by experimental data. Effects of friction and representative volume size were also discussed. It can be highlighted that using a numerical homogenization technique, the variation of the transverse mechanical effective property versus fiber volume fraction has been determined based on the microscopic transverse behavior of bulk aramid fibers. Finally, power relationships describing effective transverse Young's modulus E¯ and apparent strain ε¯ versus the normalized fiber volume fraction have been proposed and discussed. This effective homogenized material allows the development of homogenized Kevlar yarns and fabrics in the further works of homogenized approaches.

Study on the Effects of Joint Inclination and Size Effect on the Failure Process of Rock-like Materials

To explore the effects of joint inclination angle and the size on the mechanical properties and failure process of rock-like specimens, a series of uniaxial compression tests were carried out on rock-like specimens.The specimens are consist of two sizes and contain three parallel joints with various inclination angles. During testing, the variation characteristics of apparent strain field of specimens is recorded by digital image correlation (DIC) system. Testing results reveal the uniaxial compression strength of the specimen decreases gradually with the joint inclination increases from 0° to 60°, while increasing gradually with the joint inclination increases from 60° to 90°. In addition, the peak compression strength of the large-size specimens is obviously lower than that of the small-size specimen when the joint inclination angle is 0°~30°. By contrast, the peak compression strength of the large-size specimens is the same as that of the small-size specimen when the angle is 30°~60°, approximately. But, the peak compression strength of large-size specimen is obviously higher than that of small-size specimen when the joint inclination angle is between 60° and 90°. Finally, five different types of cracks are observed in this work, i.e., tensile crack,airfoil tension crack,pull-shear mixing crack,secondary crack and far field tensile crack.

The novel Ti-based metallic glass with excellent glass forming ability and an elastic constant dependent glass forming criterion

Glass forming ability (GFA) of metallic glasses is a central topic for engineering applications and understanding glassy nature. Here, we report a series of Ti-based bulk metallic glasses (BMGs, (Ti41Zr25Be26Ni8)100-xCux) with excellent GFA and mechanical properties. The (Ti41Zr25Be26Ni8)93Cu7 glassy rod with 52 mm in diameter and 75 mm in length was successfully prepared by copper mould casting, and exhibits remarkable high yield strength, apparent plastic strain and high specific strength of 2182 MPa, 2.1% and 4.06 × 105 N·m/kg, respectively. Meanwhile, the (Ti41Zr25Be26Ni8)93Cu7 BMG shows larger values of reduced glass transition temperature, γ parameter and lower Gibbs free energy that indicates smaller driving force for crystallization, these results are in well agreement with its exceptional GFA. In addition, it has revealed that Poisson's ratios of the glassy alloys is strongly correlated with GFA. Furthermore, it shows that Ti-based metallic glasses with higher Poisson's ratios generally exhibit better GFA in the same glass forming system. The present results provide robust BMG-candidates for material science and engineering application where require large critical diameters. And the novel GFA-criterion based on the correlation between Poisson’ ratio and GFA would provide guideline for developing new Ti-based BMGs.

In Situ Small-Angle Neutron Scattering Investigation of Adsorption-Induced Deformation in Silica with Hierarchical Porosity.

Adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in situ small-angle neutron scattering (SANS) and in situ dilatometry. Monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally ordered cylindrical mesopores and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A H2O/D2O adsorbate with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in situ dilatometry result from a combination of axial and radial mesopore deformation together with micropore deformation. Strain data were quantitatively analyzed with a theoretical model for micro-/mesopore deformation by combining information from nitrogen and water adsorption isotherms to estimate the water–silica interaction. It was shown that in situ SANS provides complementary information to dilatometry and allows for a quantitative estimate of the elastic properties of the mesopore walls from water adsorption.