Measurement Of Material Properties Research Articles

Estimation of Confidence Intervals and Lower Bounds for Various Weibull Percentiles

The design allowables are derived statistically from measured material properties, and the Weibull distribution is one of the most commonly used distributions for statistical modeling. A- and B-basis design allowables are frequently used; they correspond to the confidence lower bounds for the 1st and 10th percentiles, respectively, with a confidence level of 95%. The maximum likelihood method is generally recommended and commonly used for parameter and confidence lower bound estimation. On the other hand, designers are also interested in confidence lower bounds for other percentiles, and in general, confidence intervals to specify uncertainty in percentile estimates. Monte-Carlo simulation methods have been proposed for this purpose; however, they are not easy to code and take a long time to run to obtain reliable results. As an easy-to-use alternative, this study proposes approximate polynomial functions of sample size for various percentiles and confidence levels. The coefficients of the functions are presented in tabular form for each combination of percentiles and confidence levels. They eliminate the need for simulations and provide precise confidence intervals and lower bounds for a large set of Weibull percentiles.

Breed and loading history influence in vivo skeletal strain patterns in pre-pubertal female chickens

The influence of loading history on in vivo strains within a given specie remains poorly understood, and although in vivo strains have been measured at the hindlimb bones of various species, strains engendered during modes of activity other than locomotion are lacking, particularly in non-human species. For commercial egg-laying chickens specifically, there is an interest in understanding their bones' mechanical behaviour, particularly during youth, to develop early interventions to prevent the high incidence of osteoporosis in this population. We measured in vivo mechanical strains at the tibiotarsus midshaft during steady activities (ground, uphill, downhill locomotion) and non-steady activities (perching, jumping, aerial transition landing) in 48 pre-pubescent female (egg-laying) chickens from two breeds that were reared in three different housing systems, allowing varying amounts and types of physical activity. Mechanical strain patterns differed between breeds, and were dependent on the activity performed. Mechanical strains were also affected by rearing environment: chickens that were restricted from performing dynamic load bearing activity due to caged-housing generally exhibited higher mechanical strain levels during steady, but not non-steady activities, compared to chickens with prior dynamic load-bearing activity experience. Among chickens with prior experience of dynamic load bearing activity, those reared in housing systems that allowed more frequent physical activity did not exhibit lower mechanical strains. In all groups, the tibiotarsus was subjected to a loading environment consisting of a combination of axial compression, bending, and torsion, with torsion being the predominant source of strain. Aerial transition landing produced the highest strain levels with unusual strain patterns compared to other activities, suggesting it may produce the strongest anabolic response. These results exemplify how different breeds within a given specie adapt to maintain different patterns of mechanical strains, and how benefits of physical activity in terms of resistance to strain are activity-type dependent and do not necessarily increase with increased physical activity. These findings directly inform controlled loading experiments aimed at studying the bone mechanoresponse in young female chickens and can also be associated to measures of bone morphology and material properties to understand how these features influence bone mechanical properties in vivo.

Prediction of concrete anchor pull-out failure using cohesive zone modeling

Concrete anchor pull-out failure is predicted using the cohesive zone-based finite element analysis. For anchor pull-out tests, two sets of concrete specimens are prepared according to the curing temperatures. The displacement of an anchor steel bar is measured using the digital image correlation technique, and the cone failure surface is reconstructed using a 3D scanner. For each test set of concrete specimens, material properties such as the fracture energy, compressive strength, tensile strength, and elastic modulus are obtained from the three-point bending, cylindrical compression and indirect tension tests. Based on the measured material properties, the cohesive zone-based finite element analysis captures the load–displacement relationship of the anchor pull-out and three-point bending tests without the calibration of material properties. The experimental results demonstrate that the fracture energy is an essential material property to predict the concrete anchor pull-out failure, and thus the cohesive zone-based finite element analysis can provide accurate prediction of the anchor pull-out failure.

The effects of leaflet material properties on the simulated function of regurgitant mitral valves

Advances in three-dimensional imaging provide the ability to construct and analyze finite element (FE) models to evaluate the biomechanical behavior and function of atrioventricular valves. However, while obtaining patient-specific valve geometry is now possible, non-invasive measurement of patient-specific leaflet material properties remains nearly impossible. Both valve geometry and tissue properties play a significant role in governing valve dynamics, leading to the central question of whether clinically relevant insights can be attained from FE analysis of atrioventricular valves without precise knowledge of tissue properties. As such we investigated (1) the influence of tissue extensibility and (2) the effects of constitutive model parameters and leaflet thickness on simulated valve function and mechanics. We compared metrics of valve function (e.g., leaflet coaptation and regurgitant orifice area) and mechanics (e.g., stress and strain) across one normal and three regurgitant mitral valve (MV) models with common mechanisms of regurgitation (annular dilation, leaflet prolapse, leaflet tethering) of both moderate and severe degree. We developed a novel fully-automated approach to accurately quantify regurgitant orifice areas of complex valve geometries. We found that the relative ordering of the mechanical and functional metrics was maintained across a group of valves using material properties up to 15% softer than the representative adult mitral constitutive model. Our findings suggest that FE simulations can be used to qualitatively compare how differences and alterations in valve structure affect relative atrioventricular valve function even in populations where material properties are not precisely known.

High-accuracy thermophysical property measurement technique based on Labview-3ω method

High-accuracy thermophysical property measurement technique plays a significant role in the development of new materials and structures. Especially with the emerging nanomaterials, techniques that can provide thermophysical property measurement for nanoscale structures become urgent needed. Here, a Labview-3ω technique with automatic data acquisition and thermal measurement functions on the basis of the conventional 3ω technique is developed, which greatly improves the measurement speed, accuracy, and uncertainty for a wide range of nanomaterials. This high-speed, automatic, and intelligent measurement method provides great application potential for a thermophysical property measurement of various materials.

Micro universal testing machine system for material property measurement

Universal testing machines can be used to evaluate the mechanical characteristics of raw materials and components by assessing and evaluating their performance in a variety of test methods under differing tensile or compressive stresses. The term's “universal” component refers to the various kinds of tests that an unifying testing equipment can perform. The most common are tensile and compressive strength tests.The Micro Universal Testing Machine (UTM) System is proposed for measuring the properties of composite materials in microstructures. A composite material is made up of two distinct physical and chemical properties. When they combine, they form a material that is tailored to a specific task, such as becoming stronger, lighter, or more electrically resistant. They may also help with muscle stiffness and strength.This system can assess polymeric parameters such as peak load, peak displacement, tensile strength, yield strength, and percentage of elongation by analyzing the driving property of the stepper motor. To validate the validity of the built in electro – mechanical MUTM system in the microstructure, an efficiency test is performed. The designed mini UTM system meets UTM standard 1828, according to the results of the performance test. The developed micro UTM system could be used in microstructures. The software used here is visual basics which runs as an internal programming language.

Influence of Hydrogen on Vintage Polyethylene Pipes: Slow Crack Growth Performance and Material Properties

The distribution of hydrogen and how this can be widely achieved plays a significant role in the transition from fossil fuels to clean fuel. Using the existing natural gas pipeline network can be a suitable option for countries with extensive pipeline infrastructure. This study is aimed at investigating the compatibility of the existing polyethylene (PE) distribution pipe network with hydrogen. This paper utilises the cyclic pennsylvania edge notch test (CPENT) method together with material property measurements including melting point, crystallinity, and oxidative induction time (OIT) to understand the impact of exposing two different PE pipe resins to hydrogen at different exposure times. It was found that exposure to hydrogen has a noticeable impact time to failure, while the bulk crystallinity, OIT, and melting point showed little change. A change in crystal orientation was observed, and this likely accounts for the difference in time to failure when exposed to hydrogen.

Apparatus for measurement of thermoelectric properties of a single leg under large temperature differences.

Thermoelectric (TE) devices operate under large temperature differences, but material property measurements are typically accomplished under small temperature differences. Because of the issues associated with forming proper contact between the test sample and the electrodes and the control of heat flux, there are very few reports on large temperature difference measurements. Therefore, practically relevant performance parameters of a device, namely, power output and efficiency, are estimated by temperature averaging of material properties, whose accuracy is rarely validated by experimental investigations. To overcome these issues, we report an apparatus that has been designed and assembled to measure the TE properties-Seebeck coefficient, electrical conductivity, thermal conductivity, and power output and efficiency of a single thermoelectric material sample over large temperature gradients. The sample holder-a unique feature of this design-lowers the contact resistance between the sample and the electrodes, allowing for more accurate estimates of the sample's properties. Measurements were performed under constant temperature differences ranging from 50 to 300K with the hot side reaching 673K on a metallized Mg2Si0.3Sn0.7 leg synthesized in the laboratory. To simulate practical operating conditions of a continuously loaded generator, continuous current flow measurements were also performed under large temperature differences. The temperature-averaged TE properties from standard low temperature difference measurements and the experimental TE properties agree with each other, indicating that the designed setup is reliable for measuring various thermoelectric generator properties of single TE legs when subjected to temperature gradients between 50 and 300K.

Experimental investigation of effects of indentation depth and probe tip radius on apparent young's modulus of Xenopus laevis oocytes

Throughout their lifespan cells are constantly subjected to mechanical forces. Numerous studies have been conducted to measure mechanical properties of animal cells and understand their effects of the cells’ biological processes. However, the range of the apparent Young's moduli reported in the literature spans three orders of magnitude from 0.1 kPa to 100 kPa, and no clear explanation is given for the source of variation. One of the commonly used experimental techniques to measure material properties at nano- and microscale is nanoindentation. Nanoindentation works by applying a force on a sample via a small probe and recording a force-displacement curve. Probes with different tip shapes and sizes are available. However, there is little guidance on the appropriate choice of probe geometry and size for measurement of properties of animal cells. Eukaryotic cells have a complex structure including a membrane, an actin cortex, a cytoplasm, a nucleus and a cytoskeleton which consists of microfilaments, intermediate filaments and microtubules. These components have different mechanical properties contributing to the overall properties of cells. This work focuses on the effect of tip size and indentation depth on the apparent Young's modulus of Xenopus laevis oocytes measuring approximately 1 mm in diameter. Live cell fluorescent labeling using Lifeact-EGFP and confocal microscopy was used to measure the thickness of the oocyte actin cortex which is expected to have a significant contribution to the cell's stiffness. Apparent mechanical properties were measured using the JPK NanoWizard 4 BioAFM system. Indentations 5, 100 and 400 nm deep using probes with spherical tips of 0.1, 1, and 10 μm radii were performed. Contributions of the membrane and the actin cortex on the overall mechanical properties of the oocytes are analyzed.

Toward Pactive (Passive +Active) Sensing for Improved Identification of Material Properties

Subsurface electromagnetic sensing techniques that can measure material properties of hidden layers are useful for applications such as security screening. A system combining active (radar) and passive (radiometer) sensing into one unit, or a pactive sensor, can address drawbacks of extant single mode sensors by reducing measurement ambiguity and resolving features better, thereby leading to improved identification of the hidden layer. This work investigates a technique to noninvasively extract the complex permittivity and thickness of hidden dielectrics using a pactive sensor. A proof-of-concept demonstration of an optimization-based inversion technique is used to extract the properties of an unknown, hidden layer in a multi-layered dielectric structure. The technique uses active data to estimate dielectric constant and thickness, and passive data to estimate loss tangent. The experimental setup is selected to represent a simplified single-voxel security scenario consisting of multiple dielectric layers backed by a human phantom layer (heated water). Tests using K-band prototype radar and radiometer systems yielded results with less than 5% error in the extracted dielectric constant, loss tangent and thickness of the unknown layer.

A review on high-throughput development of high-entropy alloys by combinatorial methods

High-entropy alloys (HEAs) are an emerging class of alloys with multi-principal elements that greatly expands the compositional space for advanced alloy design. Besides chemistry, processing history can also affect the phase and microstructure formation in HEAs. The number of possible alloy compositions and processing paths gives rise to enormous material design space, which makes it challenging to explore by traditional trial-and-error approaches. This review highlights the progress in combinatorial high-throughput studies towards rapid prediction, manufacturing, and characterization of promising HEA compositions. This review begins with an introduction to HEAs and their unique properties. Then, this review describes high-throughput computational methods such as machine learning that can predict desired alloy compositions from hundreds or even thousands of candidates. The next section of this review presents advances in combinatorial synthesis of material libraries by additive manufacturing for efficient development of high-performance HEAs at bulk scale. The final section of this review discusses the high-throughput characterization techniques that are used to accelerate the material property measurements for systematic understanding of the composition-processing-structure-property relationships in combinatorial HEA libraries.

Modelling of fracture intensity increase due to interacting blast waves in three-dimensional granitic rocks

The complexity of the physics of rock blasting is a longstanding modelling challenge. This work presents in detail a three-dimensional, material non-linear finite element based model for wave propagation, combined with a postprocessing procedure to determine the fracture intensity caused by blasting. The rock is described with the Johnson–Holmquist-2 constitutive model, an elastoplastic-damage model designed for brittle materials undergoing high strain rates and high pressures and fracturing; it is also combined with an instantaneous tensile failure model. Additionally, material heterogeneity is introduced into the model through variation of the material properties at the element level, ensuring jumps in strain. A detailed algorithm for the combined Johnson–Holmquist-2 and tensile failure model is presented and is demonstrated to be energy-conserving, and is complemented with an open-source MATLABTM implementation of the model. A range of sub-scale numerical experiments are performed to validate the modelling and postprocessing procedures, and a range of materials, explosive waves and geometries are considered to demonstrate the model’s predictive capability quantitatively and qualitatively for fracture intensity. Fracture intensities on 2D planes and 3D volumes are presented. The mesh dependence of the method is explored, demonstrating that mesh density changes maintain similar results and improve with increasing mesh quality. Damage patterns in simulations are self-organising, and form thin, planar, fracture-like structures that closely match the observed fractures in the experiments. The presented model is an advancement in realism for continuum modelling of blasts as it enables fully three-dimensional wave interaction, handles damage due to both compression and tension, and relies only on measurable material properties.

In vivo measurement of human brain material properties under quasi-static loading.

Computational modelling of the brain requires accurate representation of the tissues concerned. Mechanical testing has numerous challenges, in particular for low strain rates, like neurosurgery, where redistribution of fluid is biomechanically important. A finite-element (FE) model was generated in FEBio, incorporating a spring element/fluid-structure interaction representation of the pia-arachnoid complex (PAC). The model was loaded to represent gravity in prone and supine positions. Material parameter identification and sensitivity analysis were performed using statistical software, comparing the FE results to human in vivo measurements. Results for the brain Ogden parameters µ, α and k yielded values of 670 Pa, -19 and 148 kPa, supporting values reported in the literature. Values of the order of 1.2 MPa and 7.7 kPa were obtained for stiffness of the pia mater and out-of-plane tensile stiffness of the PAC, respectively. Positional brain shift was found to be non-rigid and largely driven by redistribution of fluid within the tissue. To the best of our knowledge, this is the first study using in vivo human data and gravitational loading in order to estimate the material properties of intracranial tissues. This model could now be applied to reduce the impact of positional brain shift in stereotactic neurosurgery.

In-line Process and Material Property Measurement in Injection Moulding - a Theoretical Review

ABSTRACT In running production the measurement of process and material properties in-line, is a requirement to design and implement effective process control in injection moulding. This work presents a structured thorough analysis and review of the research concerned with in-line measurements of selected processes and material properties on the injection moulding machines. This review sets the current state of art within a range of process and material properties, and identifies areas for future research. The process and material property measurements reviewed are; Viscosity, Melt temperature, pvT and Melt density. It is identified that the largest research effort has been placed on the measurement of viscosity and melt temperature, whereas pvT and melt density measurement are less developed. Finally, gaps within the literature are identified and the proposal of a direction within the field is stated.

Analysis of load-bearing safety and reliability of solid rocket motor flexible joint structure

Flexible nozzle is the thrust vector control system of a solid rocket engine, and flexible joint is the key component of its load-bearing and changing behavior. It is composed of composite rubber elastic parts with spherical annular structure and metal reinforcing parts with spherical annular structure alternately adhesive. Under the action of complex loads, the flexible nozzle exhibits highly nonlinear mechanical properties. The traditional flexible joint structure with uniform thickness is easily damaged during loading and has large negative mass and short system range. However, the load-bearing swing performance of the system, such as swing center displacement, swing moment, and fatigue life, is difficult to predict, and the safety and reliability of the joint structure cannot be guaranteed. To this end, on the basis of the measured material properties of elastic parts, the Lagrangian structural dynamics algorithm coupling material and geometrically nonlinear, the Design of Experiment multi-objective optimization algorithm and the multi-axial stress fatigue finite element numerical calculation method based on crack propagation combined to design a new lightweight variable-thickness joint. From the mechanical point of view, the failure mechanism and mode of the two joint structures are compared and analyzed, the safety factor is determined, and the load-bearing swing performance of the system is predicted. Results of the ground experiment test of the system prove that variable-thickness flexible joint has better safety and reliability.

Lot acceptance testing using sample mean and extremum with finite qualification samples

In the aerospace composites industry, new material lots are tested to determine if they are suitable for use. It is common to accept or reject the material lot by comparing the sample mean and lower extremum to reference values that are established based on an initial (qualification) sample of material property measurements. Current industry practices assume that the samples are drawn from a normal distribution with known parameters equal to the mean and standard deviation of the qualification sample: this assumption yields a producer’s risk that is too high. This article presents a two-sample method of setting these reference values, considering the sampling distribution of the qualification sample. This new method is validated through simulation which shows that it produces the correct probability of Type I error. Simulation is also used to investigate the statistical power of the new method and it is compared to others commonly used. A case study is presented to demonstrate the use of the new method using composite material data from industry.

Electro-Thermal Characterization of Dynamical VO2 Memristors via Local Activity Modeling.

Translating the surging interest in neuromorphic electronic components, such as those based on nonlinearities near Mott transitions, into large-scale commercial deployment faces steep challenges in the current lack of means to identify and design key material parameters. These issues are exemplified by the difficulties in connecting measurable material properties to device behavior via circuit element models. Here, the principle of local activity is used to build a model of VO2 /SiN Mott threshold switches by sequentially accounting for constraints from a minimal set of quasistatic and dynamic electrical and high-spatial-resolution thermal data obtained via in situ thermoreflectance mapping. By combining independent data sets for devices with varying dimensions, the model is distilled to measurable material properties, and device scaling laws are established. The model can accurately predict electrical and thermal conductivities and capacitances and locally active dynamics (especially persistent spiking self-oscillations). The systematic procedure by which this model is developed has been a missing link in predictively connecting neuromorphic device behavior with their underlying material properties, and should enable rapid screening of material candidates before employing expensive manufacturing processes and testing procedures.

Optimized design of asphalt concrete pavement containing phase change materials based on rutting performance

This paper investigated the effects of phase change materials (PCMs) on temperature field and rutting performance of asphalt concrete (AC) pavement with a focus on PCM types, contents, and locations. To quantify their effects on rut depth accumulation, a pavement finite element (FE) model was constructed with measured material properties and designed structural configuration. The implemented traffic and environmental conditions were obtained from a FE model updating scheme and a heat transfer model with the consideration of traffic speed and the phase change process. Results showed that using polyethylene glycol of 4000 molar mass encapsulated by SiO2 as the PCM to replace 10% of the aggregate in the asphalt top sublayer yielded the best rutting performance; a 14% reduction in the rut depth that was accumulated within one month after pavement construction was predicted for a typical summer case in Texas. This study also revealed that incorporating PCMs into AC does not always lead to pavement rutting performance improvement. This is because (1) the lower thermal conductivity of the PCMs can offset the benefits achieved from the increased heat capacity during phase change, and (2) PCMs will not function if they are added in layers where pavement temperature is not high enough for PCMs to undergo the phase change. Therefore, developing PCMs with higher thermal conductivity together with a judicious selection of PCM types and locations will maximize the effectiveness of the pavement temperature and rutting control.

Experimental study on additive manufactured 304L stainless steel tubular sections: Material properties and cross-sectional behavior

This paper presents an experimental investigation on the material properties and cross-sectional behavior of 304L stainless steel tubular sections additively manufactured using selective laser melting (SLM). A total of 76 tensile coupons, 76 hardness test specimens, and 25 stub columns were fabricated from 304L stainless steel powders by the SLM technique. Tension coupon tests and hardness tests were conducted to determine the mechanical properties. Residual stresses and local geometric imperfections of the stub columns were measured. The effects of coupon specimen orientations, thicknesses, and annealing conditions on the measured material properties were explored. In addition, the failure modes, ultimate load-carrying capacities and structural responses of the stub columns with four different cross-sections under axial compression were obtained and analyzed to evaluate the cross-sectional behavior. The test results of ultimate strengths were compared with the predictions calculated from the current design methods. The test results showed that the tensile strength of the coupon perpendicular to the building direction was higher than that of the coupon parallel to the building direction. Moreover, the tensile strength of the coupon increased with the increase of the coupon thickness. Considering the cross-sectional behavior, the square hollow section (SHS) and circular hollow section (CHS) had greater cross-sectional axial capacities than the rectangular hollow section (RHS) and elliptical hollow section (EHS), respectively. The introduction of a single stiffener in SHS and CHS reduced the load-carrying capacities to a certain extent.

A Study of Moisture Sorption-Desorption and Its Influence on the Dynamic Modulus and Friction Coefficient of Copper-Free Brake Pads

<div class="section abstract"><div class="htmlview paragraph">The moisture sorption-desorption kinetics of copper-free brake pads was studied in detail. The sorption-desorption behavior is dependent on the environmental temperature and humidity. At 24 °C under 54% RH, the sorption increases rapidly for a week or so identified as the first stage of sorption, enters the second stage of negligible weight gain for a month and then the third stage of rapid sorption again. With increasing moisture sorption, the pad thickness increases through the 3 stages and the dynamic modulus also increases through the 3 stages. Friction materials lose moisture rapidly at 130°C and behave like desiccants. The sorption-desorption phenomenon significantly influences the friction coefficient -- a higher moisture content leading to lower friction coefficients. It is demonstrated that the rising friction coefficient for the half a dozen braking stops at the beginning of every brake testing in general is due to moisture desorption caused by rising pad temperatures. The pads become a reservoir for releasing moisture for a long period of time during testing. As many standardized brake test procedures do not specify the moisture content of the pads, brake test repeatability and reproducibility become problematic. Also, friction material property measurements for quality control becomes problematic as the moisture content is not specified or considered. For modeling and simulation of brake friction, vibration and noise, the moisture sorption-desorption effects will have to be incorporated for reliable outcomes.</div></div>