Transverse Strain Response Research Articles

Need for transverse strain data for fitting constitutive models of arterial tissue to uniaxial tests

The study deals with the process of estimation of material parameters from uniaxial test data of arterial tissue and focuses on the role of transverse strains. Two fitting strategies are analyzed and their impact on the predictive and descriptive capabilities of the resulting model is evaluated. The standard fitting procedure (strategy A) based on longitudinal stress-strain curves is compared with the enhanced approach (strategy B) taking also the transverse strain test data into account. The study is performed on a large set of material data adopted from literature and for a variety of constitutive models developed for fibrous soft tissues. The standard procedure (A) ignoring the transverse strain test data is found rather hazardous, leading often to unrealistic predictions of the model exhibiting auxetic behaviour. In contrast, the alternative fitting method (B) ensures a realistic strain response of the model and is proved to be superior since it does not require any significant demands of computational effort or additional testing. The results presented in this paper show that even the artificial transverse strain data (i.e., not measured during testing but generated ex post based on assumed Poisson's ratio) are much less hazardous than total disregard of the transverse strain response.

Prediction of top-down crack resistance in semi-flexible pavements under coupling effect of rutted surface and temperature gradient

ABSTRACT Top-down cracking (TDC) as a severe type of cracking has been widely reported in pavements with heavy traffic loads and mixtures sensitive to rutting damages. Since the likelihood of TDC increases as a result of weak mastic, semi-flexible pavements (SFPs) grouted with cement asphalt emulsion pastes (CAEPs) were introduced in this study to evaluate its performance in prevalence or mitigation of this problem. Using laboratory tests, the material properties and rutting resistance of SFP with CAEPs were compared to the conventional asphalt mixture. Then comprehensive finite element (FE) models were employed to investigate the influence of rutting damage severity on non-uniform contact stresses and critical TDC responses. Considering various degrees of rutted surface, the critical locations of TDC were predicted based on maximum transverse and shear strain responses. The results demonstrated that the presence of a rutted surface induced the near-surface responses significantly, and the more severe rutting, the higher propensity for TDC. Besides, the location of TDC initiation was greatly influenced by the severity of the rutted surface. Finally, based on SFP performance in the surface layer, CAEP40 was recommended as the best grouting material to reduce the likelihood of TDC and rutting damage development.

Inelastic Behavior of Polyoxymethylene for Wide Strain Rate and Temperature Ranges: Constitutive Modeling and Identification.

The aim of this paper is to present experimental data and the constitutive model for the inelastic behavior of polyoxymethylene in wide strain rate and temperature ranges. To capture the non-linearity of the stress responses for both loading and unloading regimes, the composite model of inelastic deformation is utilized and further developed. The equivalent inelastic strain rate is described by the Prandtl–Eyring law, while the temperature dependence is characterized by the modified Arrhenius-type law. Generalized equivalent stress and the flow rule are formulated to capture pressure sensitivity, transverse strain and volumetric strain responses. The results obtained by the constitutive law are compared with experimental data for stress vs. axial strain from standard tension tests as well as with axial and transverse strains measured by digital image correlation. The developed composite model is able to capture the non-linearity of stress–strain curves for complex loading paths within the small strain regime. For higher strains, apart from geometrically non-linear theory, evolution laws for the volume fraction of the constituents should be modified and calibrated. For the small strain regime, the inelastic dilatation is negligible. For higher axial strain values, a decrease in Poisson’s ratio under tension and increase in it under compression are observed. The Drucker–Prager-type equivalent stress and the developed flow rule provide a better description of both the transverse and volumetric strains than that of the classical von Mises–Odqvist flow rules.

Modelling hollow thermoplastic syntactic foams under high-strain compressive loading

The mechanical response of syntactic foams comprising hollow thermoplastic microspheres (HTMs) embedded in a polyurethane matrix were experimentally examined under uniaxial compressive strain. Phenomenological strain energy models were subsequently developed to capture both the axial stress-strain and transverse strain response of the foams. HTM syntactic foams were found to exhibit increased small-strain stiffness with reduced density, revealing a highly-tuneable and extremely lightweight syntactic foam blend for applications. The foams were also found to become strongly compressible at large strains and possess a high threshold for plastic deformation, making them a robust alternative to hollow glass microsphere syntactic foams. The non-standard transverse strain relationship exhibited by HTM syntactic foams at high filling fractions was captured by Ogden-type strain energy models. The thermal characteristics of these syntactic foams were also explored with Differential Scanning Calorimetry testing which showed that HTMs have a negligible impact on the thermal characteristics of the matrix.

A Novel Hyperbolic Two-Dimensional Carbon Material with an In-Plane Negative Poisson's Ratio Behavior and Low-Gap Semiconductor Characteristics.

Poisson’s ratio is one of the fundamental features of materials, reflecting the transverse strain response to the applied certain axial strain. The materials with a negative Poisson’s ratio, also known as auxetic materials, are rare in nature and attract lots of research interest because of their unusual mechanical behavior and extensive applications in mechanical nanodevices. Here, we proposed and studied a novel hyperbolic two-dimensional graphene-like structure (GLS) showing a negative Poisson’s ratio behavior by first-principles calculation. The thermodynamic, dynamic, lattice dynamic, and mechanical stabilities of the GLS were carefully studied. In addition, we also explored the electronic structure, mechanical characteristics, and optical-electronic characteristics. The GLS not only displays a negative Poisson’s ratio in certain directions but also shows low-gap semiconductor characteristics and superior electronic conductivity. It is a potential sunscreen material because of the outstanding reflection and absorption for ultraviolet and infrared light.

Mechanics-aided digital image correlation for the investigation of piezoelectric and ferroelectric behaviour of a soft PZT

The strain response of a polarised PZT was characterised using Digital Image Correlation (DIC). The DIC algorithm is based on a global approach and regularises the displacement field using the balance equations of solid mechanics. The measurement error is reduced by correcting the displacements that are mechanically not admissible. A ferroelectric test showed that the standard deviations of strain fields remain mostly under 1.2 × 10−4 for an element size of 64 px. The standard deviation on the average value is 3 × 10−6. The strain field is homogeneous and its average value is consistent with the strain obtained from a CCD laser measurement device. The longitudinal strain, transverse strain and polarisation response of the PZT were measured for bipolar and unipolar loadings ranging from 50 to 5000 V/mm. Material properties were extracted from these measurements. This work shows the advantages of a novel 2D-DIC algorithm for piezoelectric strain characterisation.

The tendinopathic Achilles tendon does not remain iso-volumetric upon repeated loading: insights from 3D ultrasound.

Mid-portion Achilles tendinopathy (MAT) alters the normal three-dimensional (3D) morphology of the Achilles tendon (AT) at rest and under a single tensile load. However, how MAT changes the 3D morphology of the AT during repeated loading remains unclear. This study compared the AT longitudinal, transverse and volume strains during repeated loading of the tendinopathic AT with those of the contralateral tendon in people with unilateral MAT. Ten adults with unilateral MAT performed 10 successive 25 s submaximal (50%) voluntary isometric plantarflexion contractions with both legs. Freehand 3D ultrasound scans were recorded and used to measure whole AT, free AT and proximal AT longitudinal strains and free AT cross-sectional area (CSA) and volume strains. The free AT experienced higher longitudinal and CSA strain and reached steady state following a greater number of contractions (five contractions) in the tendinopathic AT compared with the contralateral tendon (three contractions). Further, free tendon CSA and volume strain were greater in the tendinopathic AT than in the contralateral tendon from the first contraction, whereas free AT longitudinal strain was not greater than that of the contralateral tendon until the fourth contraction. Volume loss from the tendon core therefore preceded the greater longitudinal strain in the tendinopathic AT. Overall, these findings suggest that the tendinopathic free AT experiences an exaggerated longitudinal and transverse strain response under repeated loading that is underpinned by an altered interaction between solid and fluid tendon matrix components. These alterations are indicative of accentuated poroelasticity and an altered local stress-strain environment within the tendinopathic free tendon matrix, which could affect tendon remodelling via mechanobiological pathways.

Sign-tunable Poisson's ratio in semi-fluorinated graphene.

Poisson's ratio is a fundamental property of a material which reflects the transverse strain response to the applied axial strain. Negative Poisson's ratio is allowed theoretically, but is rare in nature. Besides the discovery and tailoring of bulk auxetic materials, recent studies have also found a negative Poisson's ratio in nanomaterials, while their negative Poisson's ratio is mainly based on conventional rigid mechanical models as bulk auxetic materials. In this work, we report the existence of in-plane negative Poisson's ratio in a two-dimensional convex structure of newly synthesized semi-fluorinated graphene by using first-principles calculations. In addition, the sign of the Poisson's ratio can be tuned by the applied strain. Interestingly, we find that this unconventional negative Poisson's ratio cannot be explained by conventional rigid mechanical models but originates from the enhanced bond angle strain over the bond strain due to chemical functionalization. This new mechanism of auxetics extends the scope of auxetic nanomaterials and can serve as design principles for future discovery and design of new auxetic materials.

The Acute Transverse Strain Response of the Patellar Tendon to Quadriceps Exercise

The Acute Transverse Strain Response of the Patellar Tendon to Quadriceps Exercise

Strain mapping in the Achilles tendon – A systematic review

Achilles tendinopathy remains one of the most prevalent overuse injuries in elite as well as recreational athletes. Regardless of the fact that the aetiology of tendinopathy has not been fully understood, therapeutic mechanical loading programs have emerged as being the treatment of choice. In this light, mechanical properties of the tendon and their response to changes in loading or unloading have been the subject of many previous investigations. One of these properties often investigated is strain, a measure of relative deformation. By means of a systematic review, an overview was given of research in this field, with a primary objective to list the methods used and secondary aim to synthesize data on strain mapping in the Achilles tendon. Following the guidelines of the PRISMA statement, 47 articles were found appropriate for qualitative assessment. Achilles tendon strain has been investigated across a variety of contexts, including the response to exercise, walking, unloading, ageing, hormonal changes and weight. Only three studies investigated the effect of the presence of tendinopathy on strain. Ultrasound was the most often used imaging modality to measure or estimate strain. Further methodological parameters, e.g. the location of measurement, differed greatly between all different studies. Nearly all studies considered global strain. Some studies investigated the transverse strain response of the Achilles tendon. Recently, however, the role of local – intratendinous – strain distribution has been found to be of critical importance and further studies should focus on imaging modalities to investigate these local changes.

Microstructural and micromechanical characterization of IN718 theta shaped specimens built with electron beam melting

Theta-shaped specimens were additively manufactured out of Inconel 718 powders using an electron beam melting technique, as a model complex load bearing structure. Two different build strategies were employed; producing two sets of specimens. Microstructural and micro-mechanical characterizations were performed using electron back-scatter, synchrotron x-ray and in-situ neutron diffraction techniques. In particular, the cross-members of the specimens were the focus of the synchrotron x-ray and in-situ neutron diffraction measurements. The build strategies employed resulted in the formation of distinct microstructures and crystallographic textures, signifying the importance of build-parameter manipulation for microstructural optimization. Large strain anisotropy of the different lattice planes was observed during in-situ loading. Texture was concluded to have a distinct effect upon both the axial and transverse strain responses of the cross-members. In particular, the (200), (220) and (420) transverse lattice strains all showed unexpected overlapping trends in both builds. This was related to the strong {200} textures along the build/loading direction, providing agreement between the experimental and calculated results.

Tendinopathy Alters Cumulative Transverse Strain in the Patellar Tendon after Exercise

This research evaluated the effect of tendinopathy on the cumulative transverse strain response of the patellar tendon to a bout of resistive quadriceps exercise. Nine adults with unilateral patellar tendinopathy (age, 18.2 ± 0.7 yr; height, 1.92 ± 0.06 m; weight, 76.8 ± 6.8 kg) and 10 healthy adults free of knee pain (age, 17.8 ± 0.8 yr; height, 1.83 ± 0.05 m; weight, 73.2 ± 7.6 kg) underwent standardized sagittal sonograms (7.2-14 MHz linear array transducer) of both patellar tendons immediately before and after 45 repetitions of a double-leg decline squat exercise performed against a resistance of 145% body weight. Tendon thickness was determined 5 and 25 mm distal to the patellar pole. Transverse Hencky strain was calculated as the natural log of the ratio of post- to preexercise tendon thickness and expressed as percentage. Measures of tendon echogenicity were calculated within the superficial and deep aspects of each tendon site from grayscale profiles. Intratendinous microvessels were evaluated using power Doppler ultrasound. The cumulative transverse strain response to exercise in symptomatic tendinopathy was significantly lower than that in asymptomatic and healthy tendons (P < 0.05). There was also significant reduction (57%) in the area of microvascularity immediately after exercise (P = 0.05), which was positively correlated (r = 0.93, P < 0.05) with a Victorian Institute of Sport Assessment for patellar tendinopathy score. This study is the first to show that patellar tendinopathy is associated with altered morphological and mechanical response of the tendon to exercise, which is manifest by reduction in cumulative transverse strain and microvascularity, when present. Research directed toward identifying factors that influence the acute microvascular and transverse strain response of the patellar tendon to exercise in the various stages of tendinopathy is warranted.

RECOVERY OF TRANSVERSE STRAIN IN HIGH–STRESS TENDONS FOLLOWING EXERCISE

BackgroundThis study evaluated the time course of recovery of transverse strain in the Achilles and patellar tendons following a bout of resistance exercise.MethodsSeventeen healthy adults underwent sonographic examination of the...

The Acute Transverse Strain Response of the Patellar Tendon to Quadriceps Exercise

The human patellar tendon is highly adaptive to changes in habitual loading, but little is known about its acute mechanical response to exercise. This research evaluated the immediate transverse strain response of the patellar tendon to a bout of resistive quadriceps exercise. Twelve healthy adult males (mean age, 34.0 ± 12.1 yr; height, 1.75 ± 0.09 m; and weight, 76.7 ± 12.3 kg) free of knee pain participated in the research. A 10- to 5-MHz linear array transducer was used to acquire standardized sagittal sonograms of the right patellar tendon immediately before and after 90 repetitions of a double-leg parallel-squat exercise performed against a resistance of 175% bodyweight. Tendon thickness was determined 20-mm distal to the pole of the patellar, and transverse Hencky strain was calculated as the natural log of the ratio of post- to preexercise tendon thickness and expressed as a percentage. Measures of tendon echotexture (echogenicity and entropy) were also calculated from subsequent grayscale profiles. Quadriceps exercise resulted in an immediate decrease in patellar tendon thickness (P < 0.05), equating to a transverse strain of -22.5% ± 3.4% and was accompanied by increased tendon echogenicity (P < 0.05) and decreased entropy (P < 0.05). The transverse strain response of the patellar tendon was significantly correlated with both tendon echogenicity (r = -0.58, P < 0.05) and entropy after exercise (r = 0.73, P < 0.05), whereas older age was associated with greater entropy of the patellar tendon before exercise (r = 0.79, P < 0.05) and a reduced transverse strain response (r = 0.61, P < 0.05) after exercise. This study is the first to show that quadriceps exercise invokes structural alignment and fluid movement within the matrix that are manifested by changes in echotexture and transverse strain in the patellar tendon.

The time course of in vivo recovery of transverse strain in high-stress tendons following exercise

ObjectiveTo evaluate the time course of the recovery of transverse strain in the Achilles and patellar tendon following a bout of resistance exercise.MethodsSeventeen healthy adults underwent sonographic examination of the...

Overweight and obesity alters the cumulative transverse strain in the Achilles tendon immediately following exercise

This research evaluated the effect of obesity on the acute cumulative transverse strain of the Achilles tendon in response to exercise. Twenty healthy adult males were categorized into 'low normal-weight' (BMI <23kgm(-2)) and 'overweight' (BMI >27.5kgm(-2)) groups based on intermediate cut-off points recommended by the World Health Organization. Longitudinal sonograms of the right Achilles tendon were acquired immediately prior and following weight-bearing ankle exercises. Achilles tendon thickness was measured 20-mm proximal to the calcaneal insertion and transverse tendon strain was calculated as the natural log of the ratio of post- to pre-exercise tendon thickness. The Achilles tendon was thicker in the overweight group both prior to (t18=-2.91, P=0.009) and following (t18=-4.87, P<0.001) exercise. The acute transverse strain response of the Achilles tendon in the overweight group (-10.7±2.5%), however, was almost half that of the 'low normal-weight' (-19.5±7.4%) group (t18=-3.56, P=0.004). These findings suggest that obesity is associated with structural changes in tendon that impairs intra-tendinous fluid movement in response to load and provides new insights into the link between tendon pathology and overweight and obesity.

Microscale prediction of deformation in an austenitic stainless steel under uniaxial loading

Abstract In this study, the deformation behaviour of polycrystalline austenitic 316H stainless steel under uniaxial loading is investigated by means of in-situ neutron diffraction (ND) measurement and crystal plasticity-based finite element (FE) modelling. Data have been obtained for the macroscopic stress–strain response and the lattice strain evolution in the longitudinal and transverse direction relative to the uniaxial loading axis. Comparison between the model predictions and the ND measurements suggests that in most cases the FE model can predict the lattice strain evolution at the microscale and capture the general trends observed in the experiments. Both ND measurements and FE modelling simulations identify little effect of micromorphology effect on the longitudinal lattice strain evolution, while the transverse lattice strain response appears to be sensitive to the microstructure, in particular the initial crystallographic orientation of the material.

Characterization of the transverse elongation of polymeric electrostatic actuators induced by Maxwell stress

This article gives a review of the research done in our lab over the past few years on the characterization of the transverse elongation of polymeric electrostatic actuators induced by Maxwell stress. Dielectric elastomers are known to produce large transverse strains in response to Maxwell stresses and thus provide a useful form of electromechanical actuation. The transverse strain responses of dielectric elastomer based Maxwell stress actuators have been investigated. The mechanical properties of elastomer cannot be fully understood on the basis of linear elastic theories. Models of hyperelasticity that are capable of describing the large deformation of rubber-like polymer materials have been used to interpret our experimental results. Our experimental and FEA studies on elastomer film actuators have helped us to understand how both the geometry and the material properties of the elastomers influence the observed actuation capabilities. Getting a high transverse strain requires not only good material properties, but also optimized actuator/electrode geometry. Some other factors, such as the electrode properties also influence the actuator performance.

Extreme Lamé Compliance in Anisotropic Crystals

For a crystalline material, Poisson's ratio depends upon two orthogonal directions, one corresponding to the applied uniaxial stress and another for the resulting transverse strain. Interest in directions that yield a negative value leads to a consideration of extreme values and associated directions. Another indicator of a negative Poisson's ratio is the Lamé compliance, defined as the transverse strain response to a unit uniaxial stress. Where this quantity is positive, Poisson's ratio is negative and it is natural to associate a near minimum value of the ratio with a maximum of the Lamé compliance. Moreover, the stationary directions associated with the compliance bear a clearer relationship to the crystallographic directions than those of the ratio. Indeed, many of these directions are not dependent upon the elastic constants within a given crystal symmetry class. In the case of 1-cristobalite, the maximum value of the Lamé compliance is associated with such invariant stationary points. In the present work, we describe the invariant stationary directions and touch on a few of the simplest material-dependent stationary points.

Transverse strain of silicone dielectric elastomer actuators

Some dielectric elastomers produce large electric-field-induced strains that can be used for electromechanical actuation. When an electric field E is applied on an electroactive polymer film electroded on both sides, the film is subjected to a stress T due to the electrostatic force (Maxwell stress) and this causes it to deform, producing a strain in the plane perpendicular to the applied field. We have measured the transverse strain responses of silicone (Dow Corning HS III) Maxwell stress actuator samples of different sizes over a wide displacement range and a frequency range from DC up to 100 Hz. The static and dynamic strain responses of the materials to a variety of driving electric flelds such as step fields, AC fields and DC bias fields have been measured as functions of amplitude and frequency. The effect of a mechanical tensile pre-load on the transverse strain has also been investigated. A pre-load initially causes an increase in the strain but the strain decreases when larger values of pre-load are applied. Numerical finite element simulations of the material using the commercial software package ANSYS and suitable models of hyperelasticity provide good agreement with most of our observations on the electric field and pre-load dependencies of the transverse strain.