Uniaxial Strain Tests Research Articles

Thermal Effect on the Compaction Behavior of Tight Shale by Uniaxial Strain Test

In order to investigate the compaction behavior of tight shale and obtain the apparent preconsolidation stress and critical stress of brittle-ductile transition, uniaxial strain tests were conducted at various temperatures. This method utilizes a cold-stretched 45# carbon steel sleeve to restrain the lateral deformation of tight shale, which successfully simulates the rigid constraints of rock stratum and overcomes the challenging issues of measuring the apparent preconsolidation stress and brittle-ductile transition based on existing tests. The results show that (1) the test curve can be divided into three stages: the pore compaction stage, the elastic compaction stage, and the cataclastic flow stage; (2) there is no obvious relationship between the front in situ stress coefficient and temperature, whereas the middle and later in situ stress coefficients increase at elevated temperatures; and (3) the apparent preconsolidation stress and critical stress of brittle-ductile transition decrease as the temperature rises, as does the elliptical yield surface of tight shale. In addition, the thermal stress distribution law of rock units was thermodynamically analyzed. The average increase in axial thermal stress is nearly equivalent to the decrease in apparent preconsolidation stress at various temperatures, and thermal stress has a compensating effect on the axial load. A new method is provided for studying the compaction behavior of tight rock under various coupling conditions.

Comprehensive research on the failure evolution of the floor in upper mining of deep and thick coal seam

The Group A coal seam represents one of the most important coal deposits of the Huainan coalfield. It poses a series of dynamic geohazards during mining operations due to its thickness, stratification, and depth location. One of the major issues is the susceptibility of the coal floor to failure under the combined action of mining and pressurized water. At greater depths, the stress becomes concentrated at the tip of the primary fractures under the influence of the high surrounding pressure. The exploitation of coal has caused new fissures to develop along the primary fissures, with energy regrouping occurring at the tips of the new fissures. To better understand the rock deformation and failure of the coal floor, uniaxial loading strain tests were performed on a standard rock specimen based on the Brillouin optical frequency domain analysis (BOFDA) to capture the deformation characteristics on the surface of the rock specimen with high accuracy. During loading, the strain of the fiber optic at peak strength was equal to 4281 με. To further study the evolution of the failure of the coal floor rock stratum during mining, electrodes, and distributed fiber optic were placed in the coal floor monitoring borehole of the coal seam to record the changes in the current and strain. The monitoring results indicate that during the initial stage, when the working face was close to the monitoring borehole, the abutment pressure of the surrounding rock mass gradually increased, the strain increased, and the current value steadily rose. During the middle stage of the monitoring process, the working face was located above the monitoring hole, the upper part of the hole was under compressive strain, the current value increased, the bottom of the hole was under tensile strain, and the electrode current showed fluctuating values. At the late stage of the monitoring process, the working face was located in proximity to the monitoring hole and the mudstone layer. The current value dropped below 1 mA, and the peak tensile strain reached 8589 με, which was followed by an abrupt change, showing the characteristics of rock failure. Comprehensive diagnosis indicated that the maximum floor failure depth was at the 21.0 m mark. During mining, the electrical current and the strain values had a positive correlation when the rock at the bottom was not failure. However, these values suddenly changed after the rock failed. The obtained results can serve as guidance for borehole multi-field monitoring in mining engineering.

Determination of Forming Limit Curves - Strain Path and Failure Analysis

With the goal to define a cost-effective and efficient process to identify adequate materials for sheet metal forming processes, it is crucial to evaluate the formability of materials. Forming limit curves (FLC) are used to analyze the forming and failure limits of sheet metals and dependence of the major (φ1) and minor strain (φ2) from the uniaxial stress-strain area through the plane-strain point to the biaxial strain area. According to ISO 12004-2, the FLC is performed by Nakajima or Marciniak tests. Due to the experimental setup and the preconditions, pre-stretching occurs in the specimens and bending and friction effect are the result. The determination of the onset of necking (FLC) results mathematically from a “best-fit inverse parabola” on section lines. In addition, the failure point, i.e. the maximum strain value one frame before failure, is also analyzed. In contrast, tensile, notched tensile and hydraulic bulge tests, which together have a potential to map an alternative FLC, exhibits a linear strain path evolution. The behavior of the various strain paths of Nakajima and the alternative methods are examined for necking and cracking. Furthermore, the fracture surfaces are investigated by confocal laser scanning microscopy to identify influences of the different FLC methods on the fracture mechanics. FLCs were conducted with the Nakajima and the alternative FLC characterization method for a ductile steel (DX54D). To ensure transferability, the tensile tests are also performed with a high-strength steel (DP800). The FLC of the ductile steel, generated through the alternative method, exhibits a similar shape to the Nakajima generated FLC with the advantage of a constant strain rate leading to linear strain paths and a lower number of tests. The same results are achieved for the uniaxial strain tests with DP800.

Bending and uniaxial tensile strain effects on the critical current of REBCO coated conductor tapes

Bending tolerance is one of the most fundamental mechanical properties of REBCO coated conductors for application to a superconducting coil. In this study, we investigated critical current degradation of REBCO coated conductors under bending and uniaxial tensile strain at 77 K and self-field with three different kinds of production from SuperPower Inc, Suzhou Advanced Materials Research Institute (SAMRI) and Shanghai Superconductor Technology (STT), respectively. All the tapes showed better bending tolerance under compressive strain than tensile strain, particularly for STT tapes, which showed no Ic degradation in compressive bending strain even with bending radius of 4.5 mm, but a 5% Ic degradation in tensile strain with bending radius of 6–6.5 mm. A uniaxial tensile strain test was also carried out to verify the dependence of Ic under tensile bending strain, the test results showed a good agreement between them. The tensile strain tolerance was 0.28–0.29% for STT tapes, 0.4–0.43% for SAMRI tapes, and 0.5–0.55% for SuperPower tapes.

Determination Method of Elasto-Plastic Correction Factor of TA16 Titanium Alloy Based on RCC-M Code Methodology

Abstract In the code for nuclear equipment, the elasto-plastic correction factor KE is a correction factor when the stress range exceeds the yield limit for simplified elasto-plastic fatigue analysis. The parameters and expressions of KE for commonly used materials (such as austenitic stainless steel) are given in the RCC-M and ASME codes, but the parameters of KE for titanium alloy materials are lacking. Based on the cyclic elasto-plastic constitutive model of Z2CND18.12 (nitrogen control) and KE parameters of austenitic stainless steel given in the code, considering various sensitive factors, a numerical calculation method for determining KE correlation coefficient is established. The elasto-plastic constitutive model of TA16 alloy with nonlinear kinematic hardening was established by the uniaxial tension, strain, and stress cycling tests of TA16 titanium alloy. Based on the numerical calculation method of KE and the constitutive model of TA16 titanium alloy, the expression and correlation coefficient of KE for TA16 titanium alloy were determined.

The rate of tendon failure in a collagen fibre recruitment-based model

Accurate characterization of the mechanical response of collagenous tissues is critical for investigations into mechanisms of soft tissue injury. These tissues are inherently viscoelastic, exhibiting strain-rate dependent stiffnesses, creep, and stress-relaxation. The strain-rate features of the failure portion of the stress-strain curve are less well developed. Collagen-distribution based models are improving and capable of reproducing the non-linear aspects of the elastic response of soft tissues, but still require parameterization of failure regions. Therefore, the purpose of this investigation, was to determine whether the parameters characterizing the rate of damage accumulation in a collagen-distribution model are proportional to strain rate.Fifty rat tail tendons were subjected to one of five different strain rates (0.01, 0.05, 0.1, 0.15, 0.20 s−1) until failure in an uni-axial strain test. To test the hypothesis that the parameters associated with damage rate are proportional to strain rate, a collagen distribution model was employed with the parameters describing the rate of fibre damage being obtained by least-squares and regressed against the strain rate.The breaking function was found to be proportional to strain rate, with a proportionality constant of 60.7 s−1. Properties characterizing the failure portion of the stress-strain curves for rat tail tendons are also reported. The Young's Modulus did not vary with strain rate and was found to be 103.3 ± 49.5 MPa. Similarly, failure stresses and strains did not vary across the strain rates tested, and were 15.6 ± 6.1 MPa and 32.2 ± 9.1%, respectively.

Percutaneous endovascular delivery of calcium chloride to the intact porcine carotid artery: A novel animal model of arterial calcification.

The present study evaluated the effect of endovascular administration of calcium chloride to the carotid artery of swines, to create a model of arterial calcification. Fifteen Large White pigs were used for the study. Via endovascular treatment, carotid arteries were exposed during 9 min to either calcium chloride (experimental artery) or saline (control artery) with the use of the TAPAS catheter. Intravascular ultrasound (IVUS) imaging was obtained at baseline, postprocedure and at 30 days. Optical coherence tomography (OCT) imaging was obtained in vitro after carotids were harvested. Longitudinally cut parallel arterial segments were placed in a system of delicate clamps and underwent uniaxial strain test. All arteries underwent histopathological examination. Calcium chloride treated segments showed extensive circumferential parietal calcification evident on both IVUS and OCT. Reduction in minimal lumen area on IVUS was evident in experimental arteries both at 24 hr and 30 days postprocedure. Histopathologic assessment (Von Kossa stain) confirmed medial calcification with mild intimal thickening. Biomechanical testing showed treated segments to have smaller breaking strength and less elastic deformation than controls. We developed a nonexpensive, reproducible model of early carotid medial calcification in pigs. Our model has the potential to help the development of research to unravel mechanisms underlying arterial calcification, the use of current or new devices to treat calcified lesions as well as to serve as an option for training interventionalists on the use of such devices.

First-principles analysis of structural stability, electronic and phonon transport properties of lateral MoS2-WX2 heterostructures

We performed first-principles-based methods to study the structural stability, electronic and phonon transport properties of lateral transition metal dichalcogenides. Specifically, we focused on the interface at the MoS2-WX2 heterostructures, where X = S or Se. The structures underwent pseudo uniaxial strain testing for compression and tension from 0 to 10% at 2% intervals. The electronic and phonon densities of states were calculated at each interval in comparison with the unstrained structure. Computational results provide insight into the effect of uniaxial strain on structure, electronic and phonon transport processes, causing a crucial impact of use of the materials in electronic devices. In addition, combining the calculated force constants with the atomistic Green's function method reveals interfacial thermal transport at the heterostructure and its underlying phonon mechanisms.

Gilding with Graphene: Rapid Chemical Vapor Deposition Synthesis of Graphene on Thin Metal Leaves

AbstractGilding is the ancient process of coating intricate artifacts with precious metals. Fascinating Egyptian and Chinese sculptures, coated with <200 nm thin metal films by this process, have resisted corrosion, wear, and other environmental degradations for thousands of years. Here, 150 nm thin palladium leaves are enriched by doped with a single layer of graphene. Commercially available Pd leaves are uniquely suited for graphene synthesis by a highly dynamic chemical vapor deposition process. The Pd leaves made by high strain rate beating are stable at high synthesis temperature, resisting solid‐state dewetting owing to their extremely low grain triple junctions density (0.017 µm−1). Mathematical models of growth kinetics guide the development of extremely rapid synthesis conditions, resulting in the formation of high‐quality graphene on Pd in less than a minute, owing to the graphene grains growing twice as fast as copper‐catalyzed growth. The graphene monolayer on the leaf increases the effective surface modulus by 59% to 236 GPa. Uniaxial strain testing with Raman spectroscopy reveals the excellent crystallinity of graphene by probing the stress‐induced phonon shifts. This new material could open exciting opportunities in utilizing high‐quality 2D materials to coat large structures.

Ruido magnético Barkhausen para el estudio de la anisotropía magnética en aceros inoxidables

RESUMEN El ruido magnético Barkhausen (RMB) es un fenómeno que ocurre en materiales ferromagnéticos cuando se someten a campos magnéticos lentamente variables, generándose cambios en su magnetización, produciéndose “saltos” discretos. Estos saltos se generan por el movimiento de las paredes de los dominios magnéticos. Se detectan colocando una pequeña bobina sobre la superficie de la muestra. El movimiento de las paredes es regulado por la microestructura del material (precipitados, tamaño de grano, tensiones residuales, etc.). Es esta manera indirecta la que permite caracterizar al material. En este trabajo se presentan las mediciones del RMB para estudiar la anisotropía magnética, inducida por el proceso de laminación, y los cambios producidos por deformación plástica uniaxial en probetas de aceros inoxidables ferríticos AISI: 409, 430, 441A. Las mediciones se realizaron a diferentes porcentajes de deformación, con el fin de observar cómo cambian las características de las señales de RMB. Se presentan también los estudios métalográficos y de dureza. Los resultados muestran una clara tendencia en relación con la dirección de los esfuerzos principales.

Discrete element modeling of grain crushing and implications on reservoir compaction

Depletion-induced formation compaction is a concern for production in hydrocarbon reservoirs. In this study, numerical mechanical tests and digital samples are proposed as an alternative to uniaxial strain experiments for investigating the effects of compaction. We propose a grain crushing model with two-sized subgrains based on the discrete element method and bonded-particle model (DEM-BPM) and perform numerical single grain crushing tests to calibrate the model parameters against the experimental sand grain characteristic strength. Numerical uniaxial strain tests are used to predict porosity and permeability reduction caused by reservoir compaction. Grain crushing incurs a significant reduction of porosity under the uniaxial strain stress path, which becomes more evident for digital samples consisting of larger grains. The stress-dependent changes in porosity and permeability obtained from the DEM simulations can be used as inputs for a reservoir-scale correlation to predict the productivity loss due to reservoir compaction.

3D Printed, PVA⁻PAA Hydrogel Loaded-Polycaprolactone Scaffold for the Delivery of Hydrophilic In-Situ Formed Sodium Indomethacin.

3D printed polycaprolactone (PCL)-blended scaffolds have been designed, prepared, and evaluated in vitro in this study prior to the incorporation of a polyvinyl alcohol–polyacrylic acid (PVA–PAA) hydrogel for the delivery of in situ-formed sodium indomethacin. The prepared PCL–PVA–PAA scaffold is proposed as a potential structural support system for load-bearing tissue damage where inflammation is prevalent. Uniaxial strain testing of the PCL-blended scaffolds were undertaken to determine the scaffold’s resistance to strain in addition to its thermal, structural, and porosimetric properties. The viscoelastic properties of the incorporated PVA–PAA hydrogel has also been determined, as well as the drug release profile of the PCL–PVA–PAA scaffold. Results of these analyses noted the structural strength, thermal stability, and porosimetric properties of the scaffold, as well as the ability of the PCL–PVA–PAA scaffold to deliver sodium indomethacin in simulated physiological conditions of pH and temperature. The results of this study therefore highlight the successful design, fabrication, and in vitro evaluation of a 3D printed polymeric strain-resistant supportive platform for the delivery of sodium indomethacin.

Burial depth interval of the shale brittle\u2013ductile transition zone and its implications in shale gas exploration and production

Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often determined by brittle mineral content (for example, quartz and feldspars) in shale gas exploration. However, the shale brittleness is also controlled by burial depth. Shale brittle/ductile properties such as brittle, semi-brittle and ductile can mutually transform with burial depth variation. We established a work flow of determining the burial depth interval of brittle–ductile transition zone for a given shale. Two boundaries were employed to divide the burial depth interval of shale brittle/ductile properties. One is the bottom boundary of the brittle zone (BZ), and the other is the top boundary of the ductile zone (DZ). The brittle–ductile transition zone (BDTZ) is between them. The bottom boundary of BZ was determined by the over-consolidation ratio (OCR) threshold value combined with pre-consolidation stress which the shale experienced over geological time. The top boundary of DZ was determined based on the critical confining pressure of brittle–ductile transition. The OCR threshold value and the critical confining pressure were obtained from uniaxial strain and triaxial compression tests. The BZ, DZ and BDTZ of the Lower Silurian Longmaxi shale in some representative shale gas exploration wells in eastern Sichuan and western Hubei areas were determined according to the above work flow. The results show that the BZ varies with the maximum burial depth and the DZ varies with the density of the overlying rocks except for the critical confining pressure. Moreover, the BDTZ determined by the above work flow is probably the best burial depth interval for marine shale gas exploration and production in Southern China. Shale located in the BDTZ is semi-brittle and is not prone to be severely naturally fractured but likely to respond well to hydraulic fracturing. The depth interval of BDTZ determined by our work flow could be a valuable parameter of shale gas estimation in geology and engineering.

Development of a Global Indicator to Assess Mechanical Tests

Full-field measurement methods have emerged in the last years and these methods are characterized by directly providing displacement and strain fields for all points over the specimen surface. Thus, the design of heterogeneous tests can be performed for material parameter identification purposes since the inhomogeneous strain fields can be measured. However, (i) no defined criterion yet exists for designing new heterogeneous tests, (ii) it is rather difficult to compare and rate different tests and (iii) a quantitative way to define the best test for material behavior characterization of sheet metals has yet to be proposed. Due to this, the goal of this work is the development of a global indicator able to assess mechanical tests. The proposed indicator quantifies the strain state range, the deformation heterogeneity and the strain level achieved in the test, based on a continuous evaluation of the strain field up to rupture. This global indicator was applied to rank some classical tests, such as uniaxial tensile, simple shear, plane strain and biaxial tensile tests. These tests were carried out numerically by reproducing the virtual behavior of DC04 mild steel. A constitutive model composed by the non-quadratic Yld2004-18p yield criterion combined with a mixed isotropic-kinematic hardening law and a macroscopic rupture criterion was used. The performance of the tests was compared with the indicator and a ranking was established. The results obtained show that biaxial tension is the test providing more information for the mechanical behavior characterization of the material. It was also verified that plane strain test presents a better performance than simple shear and uniaxial tensile tests.

Low-temperature properties of plant-produced RAP mixtures in the Northeast

The impact of reclaimed asphalt pavement (RAP) materials on pavement performance is an important topic of study in the industry due to environmental and cost benefits. The primary concern for increasing allowable RAP percentages in hot mix asphalt relates to the presence of aged materials, which may embrittle the mixture and decrease cracking resistance. Low-temperature cracking is a major distress in cold temperature climates, such as the Northeastern United States. Currently, there are several procedures to analyse low-temperature performance of asphalt binders and mixtures. However, these methods use different starting (initial) temperatures and cooling rates that may not represent actual field temperatures and cooling rates. This paper presents the results of a study on low-temperature performance of plant-produced RAP mixtures. Eighteen mixtures from three states were tested with varying RAP contents (0–40%) and different virgin binder grades. The objectives of the study were to: (1) evaluate the impact of cooling rate and starting temperature on the critical cracking temperature of RAP materials; (2) evaluate the impact of RAP content on the low-temperature properties of mixtures; (3) evaluate the benefit of using softer virgin binder grades to mitigate the impact of the aged RAP binder in the mixture; and (4) to compare the low-temperature cracking properties determined from different mixture and binder tests. Based on the results, warmer starting temperatures and faster cooling rates result in warmer critical cracking temperatures for all mixtures. Through use of the uniaxial thermal stress strain test, it was found that the addition of RAP alters fracture behaviour from ductile failure towards a brittle failure. Based on results from the indirect tensile test, tensile strength increases with RAP content. However, due to a faster-building thermal stress, warmer critical cracking temperatures result. It was also determined that degree of blending may impact the effectiveness of using softer binder grades at higher RAP percentages to improve low temperature cracking resistance. The data also show that analysis procedure and test protocols can have a profound effect on critical cracking temperature. The conclusions presented reinforce the need for more accurate representation of RAP materials, and careful selection of analysis parameters.

Histologic, histochemical, and biomechanical properties of fragments isolated from the anterior wall of abdominal aortic aneurysms

To analyze biomechanical, histologic, and histochemical properties of anterior fragments of abdominal aortic aneurysms (AAA) and to correlate them with the maximum transverse diameter (MTD) and symptoms associated to the aneurysms. Fragments of the anterior aneurysm wall were obtained from 90 patients submitted to open repair of AAA of degenerative etiology from 2004 to 2009 in the Clinics Hospital of São Paulo University Medical School. Two specimens were produced from the fragments: one for histologic analysis for quantification of collagen fibers, elastic fibers, smooth muscle cells, and degree of inflammatory activity and the other for uniaxial tensile test to assess biomechanical failure properties of the material, such as strength, tension, and stress. Cases were classified according to symptoms and to the AAA MTD. Fragments from AAA with MTD < 5.5 cm showed higher values for biomechanical failure properties than those of AAA with MTD < 5.5 cm (strength, 5.32 ± 2.07 × 4.1 ± 2.41 N; tension, 13.83 ± 5.58 × 10.82 ± 6.48 N/cm; stress, 103.02 × 77.03 N/cm(2); P < .05). No differences were observed between the groups in relation to failure strain (0.41 ± 0.12 × 0.37 ± 0.14; P = .260) and thickness of the fragments (1.58 ± 0.41 × 1.53 ± 0.42 mm; P = .662). The average values of fiber compositions of all the fragments were as follows: collagen fibers, 44.34 ± 0.48% and 61.85 ± 10.14% (Masson trichrome staining and Picrosirius red staining, respectively); smooth muscle cells, 3.46 ± 2.23% (immunohistochemistry/alpha-actin); and elastic fibers, less than 1% (traces) (Verhoeff-van Gieson staining). No differences in fiber percentages (collagen, elastic, and smooth muscle) were observed in fragments from AAA with MTD <5.5 cm and <5.5 cm, but more intense inflammatory activity was seen in larger AAA (grade 3; 70% × 28.6%; P = .011). Compared with asymptomatic aneurysms, symptomatic aneurysms showed no differences in the biomechanical failure properties (strength, 5.32 ± 2.36 × 4.65 ± 2.05 N; P = .155; tension, 14.08 ± 6.11 × 12.81 ± 5.77 N/cm; P = .154; stress, 103.02 × 84.76 N/cm(2); P = .144), strain (0.38 ± 0.12 × 0.41 ± 0.13; P = .287), thickness of the fragments (1.56 ± 0.41 × 1.57 ± 0.41 mm; P = .848), and histologic composition (collagen fibers, 44.67 ± 11.17 × 44.02 ± 13.79%; P = .808; smooth muscle fibers, 2.52 × 2.35%; P = .751; elastic fibers, <1%) Fragments of the anterior wall from larger aneurysms were more resistant than those from smaller AAA, with no tissue properties that could explain this phenomenon in the histologic or histochemical analyses utilized. The fragments of the anterior midsection from larger aneurysms were more resistant than those from smaller abdominal aortic aneurysms, with no tissue properties that could explain this phenomenon in the histologic or histochemical analyses. Larger aneurysms, at least in this place may be stronger than smaller aneurysms. It could point toward regional differences (heterogeneity, localized pathologies) as an important player in aneurysm rupture. Uniaxial strain tests are an important tool for the comprehension of a complex behavior such as that from an aneurysmal aortic wall. However, these tests still have limitations in providing information that would allow the calculation of the risk of rupture for abdominal aortic aneurysms.

Irreconcilability of uniaxial test data with irreversibility of loading and unloading

Uniaxial material properties of macroscopic average stress and strain invoke monoscale global equilibrium. The procedure does not hold for microscopic uniaxial stress and strain test specimens. There lacks direct connection between the measured stress and strain at the macro and micro scales. Scale transmissibility of stress and strain must be validated by models and/or laws. Material testing philosophy of the 18th century are not valid for the 21st century applications, where microscopic and nanoscopic effects enter into design. Simply put, the dual scaling of distortion (micro) and dilatation (macro) is no longer uncommon.The use of true versus engineering stress and strain (S&S) can be troublesome as they entail contrasting physical interpretation for the same material, say for the 4130 steel for example. The true S&S curve shows hardening while the engineering S&S curves exhibit softening. The fictitious concept of elastic and plastic unloading also renders different meanings. Dissipated and available energy density from the uniaxial data can yield positive and negative efficiencies for 4130 steel. The benefit of micro and/or nano effects to macro properties can depend on the sustainable time of the test data. The active holding time of the nano interface reinforcement depends on manufacturing know-how, a highly guided trade secret that cannot be commonly acquired without the analytical skill and knowledge of non-equilibrium mechanics and metallurgy.The competition of the 21st century rests on energy efficiency for the use of super strength materials and structural systems. The axiomaticism of material testing can no longer walk alone without the emphasis of “identifiability and synchronicity” (I&S) of I-Ching or the Books of Changes. Uncertainties are not likely to be revealed by postulating and testing models without a knowledge of I&S. Physical events are biased by synchronicity, a property that can mitigate uncertainty. As application is extended from the macro to the nano or even smaller scale, multiscaling models will be the rules in material science research rather than the exception.

Validation of a Pressure Diameter Method for Determining Modulus and Strain of Collagen Engagement for Long Branches of Bovine Pulmonary Arteries

Recent studies have shown that capacitance measurements of large arteries provide better prognosis and diagnosis than tests of resistance alone in pulmonary hypertension (Mahapatra et al., 2006, "Relationship of Pulmonary Arterial Capacitance and Mortality in Idiopathic Pulmonary Arterial Hypertension," J. Am. Coll. Cardiol., 47(4), pp. 799-803; Reuben, 1971, "Compliance of the Human Pulmonary Arterial System in Disease," Circ. Res., 29, pp. 40-50]. Decreased arterial capacitance causes increased load to the heart and is the direct result of increased stiffness and elastic modulus of the arterial wall. Here, we validate a pressure-diameter (PD) method for comparing the elastic modulus and collagen engagement for post-hilar pulmonary arteries with a large range of arterial diameter. The tissue mechanics of the post-hilar arteries are not well-characterized in pulmonary hypertension. It is believed that future studies with this method will provide useful insight into the role of passive tissue mechanics of these arteries in the pathophysiology of pulmonary hypertension, eventually improving clinical diagnosis, prognosis, and treatment. Post-hilar pulmonary arteries, excised from healthy and hypertensive calves and healthy cows, were inflated over a range of 0 [mm Hg] to 110 [mm Hg] in an isolated tissue bath. Internal pressure was recorded with an electric pressure catheter. Artery diameter and longitudinal stretch were recorded photographically. Stress-strain data curves were extracted using Lame's law of thick-walled tubes. Radial strips were removed from each section and tested in a uniaxial (MTS) tester for validation. Both the elastic modulus and collagen engagement strain were similar to results obtained by more traditional means. The average difference between measured values of the two methods for collagen engagement strain was 3.3% of the average value of the engagement strain. The average difference between the measured values of the two methods for modulus of elasticity was 7.4% of the average value of the modulus. The maximum, theoretical, relative error for the stress determined with the PD method was calculated at 20.3%. The PD method proved to be a suitable replacement for uniaxial strain tests in comparing collagen engagement strains. The method allowed faster testing of tissues of multiple diameters, while removing the effect of end conditions. The PD method will be of further utility in continued study of tissue mechanics in pulmonary hypertension studies.

Pull-Out Testing of SWCNTs Simulated by Molecular Dynamics

In this paper we present our results of simulating a pull-out test of single walled carbon nanotubes (SWCNT) out of a single crystal gold lattice by means of molecular dynamics. We compare the obtained force-displacement data of the pullout test to results of simulated uniaxial tensile strain tests of SWCNTs. In doing so, we make a theoretical estimation about the quality of the clamping of SWCNTs in a gold crystal. We investigated the influence of chirality of SWCNTs and of the system temperature. Dependent on SWCNT chirality two different pull-out behaviours can be described. Zigzag nanotubes show stronger pull-out resistance than chiral or armchair nanotubes. Our results indicate a minor influence of embedding length of the SWCNT in the gold matrix on pull-out forces. The system temperature has only little effect on the maximum pull-out forces. The presented results have impact on design criteria of SWCNT-metal interfaces.

Constitutive Property Behavior of Type N and Type S Mortars

Abstract An extensive program of quasi-static mechanical property tests was conducted to characterize the mechanical behavior of type N and type S mortars under various stress and strain boundary conditions to decide which mortar to use in the construction of triple-brick and brick-over-block walls. The material characterization effort consisted of hydrostatic compression, unconfined compression, triaxial compression, direct pull, reduced triaxial extension, and uniaxial strain tests. The results from all of the quasi-static tests provided the mechanical properties required for determining which mortar to use in the construction of target walls for projectile perforation experiments as well as the constitutive model coefficients for numerical simulations of these experiments. This paper provides a summary of the mechanical property test results obtained for type N and type S mortars and the rational for using type S mortar in the construction of triple-brick and brick-over-block walls.