Measurement Of Elastic Modulus Research Articles

Effects of Environmental Degradation on Flexural Failure Strength of Fiber Reinforced Composites

Fiber-reinforced composite laminates are often used in harsh environments that may affect their long-term durability as well as residual strength. In general, environmental degradation is observed as matrix cracking and erosion that leads to deterioration of matrix-dominated properties. In this work, cross-ply laminates of carbon fiber reinforced epoxy were subjected to environmental degradation using controlled ultraviolet radiation (UV) and moisture condensation and the post-exposure mechanical properties were evaluated through elastic modulus and failure strength measurements. Additionally, both degraded and undegraded were subjected to cyclic fatigue loading to investigate possible synergistic effects between environmental degradation and mechanical fatigue. Experimental results show that the degradation results in reduced failure strength. Greater effects of degradation are observed when the materials are tested under flexural as opposed to uniaxial loading. Based on strength measurements and scanning electron microscopy, we identified various damage modes resulting from exposure to UV radiation and moisture condensation, and cyclic loading. The principal mechanisms that lead to reduction in mechanical properties are the loss of fiber confinement due to matrix erosion, due to UV radiation and moisture condensation, and weakened/cracked ply interfaces due to mechanical fatigue. An empirical relationship was established to quantify the specific influence of different damage mechanisms and to clarify the effects of various degradation conditions.

Palpationlike soft-material elastic modulus measurement using piezoelectric cantilevers

We have developed an all-electrical piezoelectric cantilever sensor that can self-excite and self-detect for tissue elastic modulus measurement. An all-electrical piezoelectric cantilever is consisted of a sandwich of piezoelectric layer, e.g., lead zirconate titanate (PZT), a nonpiezoelectric layer, e.g., stainless steel, and a second piezoelectric layer. The top piezoelectric layer serves as the driving layer (self-exciting) and the second piezoelectric layer as the sensing layer (self-sensing). The driving and sensing piezoelectric layers may be of different lengths. Applying a dc voltage across the driving PZT layer causes the piezoelectric cantilever to bend. The resultant bending stress in the sensing PZT layer generates a piezoelectric voltage across the sensing PZT layer that rises rapidly to a maximum before it decays with time. The maximum induced voltage was used to measure the axial displacement of the piezoelectric cantilever. With its force generation and displacement sensing capability, we show that an all-electrical piezoelectric cantilever can measure the elastic modulus of tissues both under the regular compression geometry and the flat-punch indentation geometry. In addition, the sensor can map the local elastic modulus variations of tissues much like palpation.

Comparison of different analysis methods in nanoindentation and influence on the correction factor for contact area

The classical area function technique used for nanoindentation measurements is compared to the two-slope method, a recent method rarely used which is based on the calculation, at maximum load, of the slopes of the loading and unloading curves. Both methods are used with two different ways of calculating the unloading contact stiffness and their effects on the elastic modulus and hardness measurements are compared. The influence of these different ways of calculating on the correction factor for contact area that is present in the fundamental relationship between contact stiffness, Young's modulus and contact area is also analysed and discussed. It is confirmed on three different materials, fused quartz, titanium and magnesium oxide, that this correction factor is not only depending on the indenter geometry but also on the tested material.

Evaluation of elastic modulus of cantilever beam by TA-ESPI

The paper proposes an evaluation technique for the elastic modulus of a cantilever beam by vibration analysis based on time average electronic speckle pattern interferometry (TA-ESPI) and Euler–Bernoulli equation. General approaches for the measurement of elastic modulus of a thin film are the Nano indentation test, Buldge test, Micro-tensile test, and so on. They each have strength and weakness in the preparation of the test specimen and the analysis of experimental results. ESPI is a type of laser speckle interferometry technique offering non-contact, high-resolution and whole-field measurement. The technique is a common measurement method for vibration mode visualization and surface displacement. Whole-field vibration mode shape (surface displacement distribution) at resonance frequency can be visualized by ESPI. And the maximum surface displacement distribution from ESPI can be used to find the resonance frequency for each vibration mode shape. And the elastic modules of a test material can be easily estimated from the measured resonance frequency and Euler–Bernoulli equation. The TA-ESPI vibration analysis technique can be used to find the elastic modulus of a material requiring simple preparation process and analysis.

Uncertainty estimation in measurement of micromechanical properties using random-fuzzy variables

Instrumented indentation testing mechanical properties of small volume materials can be affected by various factors during the measurement process, either in random or nonrandom characteristics, which can induce much uncertainty in the evaluation results. The traditional uncertainty estimation method, which is based on probability theory, is ineffective for the cases where some nonrandom effects are present. In this article, uncertainty estimation in measurement of hardness and elastic modulus by tester for micromechanical properties associated with random-fuzzy variables (RFVs) is presented. Uncertainty estimation results from both the traditional and RFV methods are derived and compared. Results show that the measurement uncertainties in hardness and elastic modulus can be effectively expressed in terms of RFVs under different levels of confidence, and all possible influencing effects on the uncertainties can be involved.

A novel method for the measurement of elastic moduli of fibres

Abstract The elastic modulus of fibres used in composite materials is a parameter of prime importance in the determination of overall mechanical behaviour. However, evaluation of Young’s modulus, E, of a fibre is a delicate operation given the small dimensions (diameter typically a few tens of microns), and therefore low forces involved in tensile testing. This article treats a novel method of modulus assessment involving the bending of fibres, clamped at one extremity, by forced vibrations. The fibre behaves as a beam, and when the forced oscillations approach (one of) the resonant frequency(ies) of the fibre, the bending amplitude increases. Classical beam theory allows evaluation of Young’s modulus from knowledge of resonant frequency, and fibre dimensions and density. Preliminary application of the technique using fibres of E-glass, having well known elastic characteristics, has given good results and shown its inherent potential. Subsequently, the technique developed was used on recycled fibres in order to obtain their Young’s modulus and to assess their loss of mechanical properties when compared to virgin fibres.

From 24-Hour Blood Pressure Measurements to Arterial Stiffness

The articles by Li et al1 and Dolan et al,2 in this issue of Hypertension and focused on the development of a new approach to estimate arterial stiffness, highlight the role of arterial mechanical properties in the determination of cardiovascular risk. In the past, arterial stiffening and increases in systolic blood pressure (SBP) and pulse pressure (PP) have been considered a part of normal aging, and no treatment for these alterations has been proposed. The pathophysiology, structural bases, and determinants of arterial stiffness have been extensively studied these last years.3–5 Although arterial stiffening is a common situation, it has now been confirmed that aortic stiffness is an independent predictor for total and cardiovascular mortality, coronary morbidity—mortality, and fatal stroke in patients with essential hypertension, diabetes mellitus, or end-stage renal failure, and in the general population in the elderly.6,7 It is therefore important to identify subjects who are at higher risk for developing arterial stiffness with aging and determine the environmental and genetic factors that can accelerate arterial stiffening. In recent years, several devices have been developed for the evaluation and measurement of arterial stiffness. Arterial stiffness can be quantified by the measurement of several parameters such as cross-sectional arterial distensibility and compliance, pulse wave velocity (PWV), analysis of pulse wave contours (mainly augmentation index and reflection waves), measurements of elastic modulus, stress-strain relationships, etc. During the past 5 years, among these approaches, PWV and augmentation index (AI) have become the most reliable for the evaluation of arterial stiffness in clinical and epidemiological studies.8 PWV depends mainly on the mechanical properties of large …

Mechanical Property Measurement of Interconnect Materials by Magnetostrictive Sensors

ABSTRACTThis paper reports on the measurement of elastic modulus for some electronic thin film materials used in electronic interconnects by a magnetostrictive sensor. Thin film materials of Au, Sn, In and Au-rich lead free solder (AuSn) were sputter deposited onto well defined strips of Metglas™. This material possesses magnetostrictive properties whereby it deforms when subjected by a magnetic field and generates a magnetic field when deformed. The MetglasTM strip is driven to resonance via a modulated magnetic field generated by a coil. The elastic modulus of the above materials was determined by measuring the resonant frequency of the sensors before and after film deposition and using the frequency shift, two analytical approaches were employed to extract values. The as sputtered films were examined by X-ray Diffraction (XRD) and Scanning Election Microscope (SEM) to characterize their microstructures. The elastic modulus of Au films was determined by employing two mathematical methodologies that resulted in values of 71.2GPa and 75.9GPa, which exhibit less than 5% divergence. Errors in the different measuring methodologies are discussed. Moreover, elastic modulus values of solder materials of AuSn (80/20 wt%), tin and indium films, which were also measured in their as deposited forms, will be discussed. This method represents a potentially new, non-destructive method to determine critical material properties of as deposited materials.

Implementation of a modern resonant ultrasound spectroscopy system for the measurement of the elastic moduli of small solid specimens

The use of mechanical resonances to determine the elastic moduli of materials of interest to condensed-matter physics, engineering, materials science and more is a steadily evolving process. With the advent of massive computing capability in an ordinary personal computer, it is now possible to find all the elastic moduli of low-symmetry solids using sophisticated analysis of a set of the lowest resonances. This process, dubbed “resonant ultrasound spectroscopy” or RUS, provides the highest absolute accuracy of any routine elastic modulus measurement technique, and it does this quickly on small samples. RUS has been reviewed extensively elsewhere, but still lacking is a complete description of how to make such measurements with hardware and software easily available to the general science community. In this article, we describe how to implement realistically a useful RUS system.

Nanoscale Inhomogeneities and Thermodynamics of Unfilled Polymer Gels

The description of the structure of swollen polymer networks and its relationship with mechanical and thermodynamic properties has been an unresolved problem for a long time. In spite of a number of theoretical approaches, no simple formalism has been found that captures the structural variety of real gels. Here we report a new approach to describe inhomogeneities in the nanometer size range that develop in the course of the cross‐linking process, and their relationship with the macroscopic elastic properties. Experimental data from small angle neutron scattering (SANS), osmotic swelling pressure, and elastic modulus measurements were obtained on polyfluorosilicone (PFSi) gels prepared by different cross‐linking processes from precursor chains of monomodal and bimodal distributions. The neutron scattering response of these gels reveals two types of concentration fluctuations, namely, those originating from nanoscale frozen‐in constraints generated by the cross‐links and the time‐dependent thermodynamic fluctuations associated with the osmotic properties of the network chains. The amplitude of the frozen‐in concentration fluctuations deduced from small angle neutron scattering measurements is found to be proportional to the ratio of the macroscopic elastic shear modulus to the osmotic compression modulus. The thermodynamic concentration fluctuations are in agreement with the results of dynamic light scattering and macroscopic osmotic pressure measurements. The present approach describes the effect of the nanoscale features on the macroscopic properties of the gel. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Measurement of elastic moduli using spherical indentation and digital speckle pattern interferometry with automated data processing

The Young's modulus and the Poisson's ratio of an isotropic material are measured using digital speckle pattern interferometry. The technique is based on the determination of the permanent local displacement field generated in a specimen after it is plastically deformed with a spherical indenter. Using a phase shifting technique and a phase unwrapping algorithm, the phase distribution coded in the speckle interferograms can be quickly obtained. By adjusting the displacement field generated by the indentation to an empirical model produced by a point force in a semi-infinite elastic medium, the values of both elastic moduli can be determined by applying a least-squares inversion method to the evaluated continuous phase distribution. The performance, accuracy, advantages and limitations of this technique are determined by evaluating the elastic moduli of bronze.

Fracture strength, elastic modulus and Poisson's ratio of polycrystalline 3C thin-film silicon carbide found by microsample tensile testing

This paper reports the measurement of elastic modulus, fracture strength, and Poisson's ratio of thin-film 3C polycrystalline silicon carbide determined by microsample tensile tests. The tensile specimens had a gage width of 600 μm, gage length of 4 mm, and gage thicknesses of 20–40 μm. A custom-built microsample tensile testing machine was used to conduct the tests and strain was measured with a laser-based direct strain measurement system. Twenty-three tests were completed on two sets of material with two different grain textures. Results of the microsample tensile tests show an average elastic modulus of 428 GPa, Poisson's ratio of 0.24 and fracture strength of 0.49 GPa for batch 1. Batch 2, a material with a different texture, resulted in an average elastic modulus of 448 GPa, Poisson's ratio of 0.17 and fracture strength of 0.81 GPa. In addition to differences in average values, variations were also seen in the Weibull characteristics of the two differently textured materials.

Measurement of residual stress and elastic modulus of polycrystalline 3C-SiC films deposited by low-pressure chemical vapor deposition

Residual stress and in-plane biaxial modulus of polycrystalline 3C-silicon carbide (poly-SiC) films are studied using bulk and surface micromachined microstructures. The poly-SiC films are deposited on 100-mm-diameter (100) silicon wafers in a high-throughput, low-pressure chemical vapor deposition furnace at 1173 K using dichlorosilane (SiH 2Cl 2) and acetylene (C 2H 2) precursors at deposition pressures from 61 to 666 Pa. The resulting 0.5 to 2.7 μm films are highly textured, (111) oriented, polycrystalline 3C-SiC. Suspended diaphragms of these films are fabricated by standard wet chemical bulk micromachining of the silicon substrate from the back side. The load-deflection technique is used to extract the residual stress and in-plane biaxial modulus. For the center slot position in the boat, the films' residual stress changes from high (e.g., 726 MPa) to a relatively lower (e.g., 265 MPa) tensile stress as the deposition pressure increases from 61 to 333 Pa at fixed precursor flow rates. The average biaxial modulus of the films is 482 GPa; accordingly, the average Young's modulus is 401 GPa, assuming a Poisson's ratio of 0.168. However, the poly-SiC diaphragms fabricated from films deposited in the 380 to 666 Pa pressure range buckle due to compressive residual stress. Therefore, micro strain gauges are also fabricated and used to measure compressive residual strains in these films, which are − 0.032% at 500 Pa and − 0.024% at 666 Pa. Using 401 GPa as Young's modulus, these correspond to residual stresses of − 129 MPa and − 98 MPa, respectively.

Mechanical Properties of Intermetallic Compounds in the Au–Sn System

The mechanical properties of intermetallic compounds in the Au–Sn system were investigated by nanoindentation. Measurements of hardness and elastic modulus were obtained for all of the confirmed room-temperature intermetallics in this system as well as the β phase (8 at.% Sn) and AuSn4. Overall, it was found that the Au–Sn compounds have lower hardness and stiffness than common Cu–Sn compounds found in solder joints. This finding is in contrast to common knowledge of “Au embrittlement” due to the formation of either AuSn4 or (Au,Ni)Sn4 intermetallic compounds. This difference in understanding of mechanical properties of these phases and the resulting joint strength is discussed in terms of reliability and possible failure mechanisms related to interface strength or microstructural effects. Indentation creep measurements performed on Au5Sn, Au–Sn eutectic (29 at.% Sn) and AuSn indicate that these alloys are significantly more creep resistant than common soft solders, in keeping with typical observations of actual joint performance.

Mechanical properties of epitaxial 3C silicon carbide thin films

Microscale tensile specimens of epitaxial 3C silicon carbide (3C-SiC) thin films were fabricated on Si substrates and tested to provide measurements of strength and elastic modulus. Samples were fabricated using both micromolding and reactive ion etching (RIE) processes to pattern the 3C-SiC films. All specimens were on the (100) plane with a <110> tensile direction. Testing was performed on a microsample tensile testing machine previously used on other materials. The samples had a thickness of 0.5 to 2 /spl mu/m, a gauge length of 4 mm, and a minimum width of 600 /spl mu/m. Testing results show an average strength of 1.19 /spl plusmn/ 0.53 GPa and 1.65 /spl plusmn/ 0.39 GPa for micromolded and RIE patterned specimens, respectively. The elastic modulus was measured to be 424 /spl plusmn/ 44 GPa, which was consistent with but slightly lower than the elastic modulus calculated with single crystal elastic constants found by ab initio calculations.

RESUSCITATION-INDUCED INTESTINAL EDEMA DECREASES THE STIFFNESS AND RESIDUAL STRESS OF THE INTESTINE

We have shown that acute edema impairs intestinal transit and we wanted to know whether this could be from changes in the physical characteristics of the intestine. Our hypothesis was that acute edema will change the physical characteristics of the intestine, which were measured by standardized engineering measures of elastic modulus, to determine stiffness and opening angle, and to determine residual stress. Rats were randomized to sham, mild edema (80 mL/ kg of normal saline resuscitation), and severe edema groups (80 mL/kg of normal saline resuscitation with intestinal venous hypertension). Segments of distal ileum were hung to a fixed point in a tissue bath and to a tensiometer and were stretched in increments of 1 mm, recording the new length and the corresponding force from the tensiometer to determine elastic modulus. Next, two transverse cuts were made yielding a 1- to 2-mm-thick ring-shaped segment of tissue and were then cut radially to open the ring. The opening angle was measured. Acute intestinal edema led to a decrease in transit, elastic modulus, and opening angle of the intestine in the absence of ischemic injury. Acute intestinal edema leads to a significant loss in stiffness and residual stress and is a plausible explanation for how acute edema impairs intestinal transit.

Effect of Carbon and Nitrogen Implantation on the Properties of Silicon Nitrides

This study focused on the effect of ion implantation on the mechanical properties of silicon nitride based ceramics. The examined materials contained 4% Al2O3, 6% Y2O3 and, in some cases, graphite or black carbon additives. Fully densified bodies were manufactured by two-step hot isostatic pressing, in other experiments pressureless sintering gave porous ceramics. Nitrogen or carbon ions with 190 keV or 350 keV were implanted, a part of samples obtained laser treatments for comparison. Measurements of elastic modulus, four point and three point bending strength were carried out at room temperature on sintered samples, partially sintered samples and sintered and oxidised samples. Carbon or nitrogen implantation influenced the strength of partially sintered samples only if the density was over 80%. Both the implantation of carbon or nitrogen ions and the laser treatment affected the bend strength of sintered samples, enlarging the power introduced its value first increased than decreased. Implantation slightly decreased the strength of samples oxidised at 1400 °C. Comparison of different mechanical characteristics may support a better understanding of phenomena during ion beam implantation or laser irradiation.

Elastic Modulus Measurements via Laser-Ultrasonic and Knoop Indentation Techniques in Thermally Sprayed Coatings

Nondestructive techniques for evaluating and characterizing coatings were extensively demanded by the thermal spray community; nonetheless, few results have been produced in practice due to difficulties in analyzing the complex structure of thermal spray coatings. Of particular interest is knowledge of the elastic modulus values and Poisson’s ratios, which are very important when seeking to understand and/or model the mechanical behavior or to develop life prediction models of thermal spray coatings used in various applications (e.g., wear, fatigue, and high temperatures). In the current study, two techniques, laser-ultrasonics and Knoop indentation, were used to determine the elastic modulus of thermal spray coatings. Laser-ultrasonics is a noncontact and nondestructive evaluation method that uses lasers to generate and detect ultrasound. Ultrasonic velocities in a material are directly related to its elastic modulus value. The Knoop indentation technique, which has been widely used as a method for determining elastic modulus values, was used to compare and validate the measurements of the laser-ultrasonic technique. The determination of elastic modulus values via the Knoop indentation technique is based on the measurement of elastic recovery of the dimensions of the Knoop indentation impression. The approach used in the current study was to focus on evaluating the elastic modulus of very uniform, dense, and near-isotropic titania and WC-Co thermal spray coatings using these two techniques. Four different coatings were evaluated: two titania coatings produced by air plasma spray (APS) and high-velocity oxyfuel (HVOF) and two types of WC-Co coatings, conventional and multimodal (nanostructured and microsized particles), deposited by HVOF.

Structure and properties of metal nitride films produced by ion implantation

—The effect of the nature of two-component fillers on the physical and mechanical properties of finegrained graphites was studied using highly oriented needle coke and nearly isotropic synthetic graphite as components of fillers. Each filler was prepared in the form of coarse (−120 µm) and fine (−10 µm) powders. Different mixtures of these components were used in producing graphite samples, which were then characterized by density, thermal expansion, compressive strength, and modulus of elasticity measurements. The results demonstrate that the thermal expansion, compressive strength, and modulus of elasticity of the graphites thus prepared depend on the microtexture, size, and shape of the filler particles.

Measurement of in-plane elastic moduli of composites with a circular disk specimen and piezoelectric sensors

Many test specimen configurations and test methods have been used for measuring the in-plane elastic constants of orthotropic composites. While the measurement of the Young's modulus is straightforward, the shear modulus determination is more difficult. Most of the experimental methods require more than one specimen for the measurement of all the in-plane elastic constants. In the proposed method, a single test specimen in the form of a circular disk is sufficient. The Young's modulus and the shear modulus are measured with piezoelectric sensors that produce and detect dilatational and shear waves, respectively. The experimental techniques involved and the possible methods of interpreting the results are explained. The results obtained were compared with those determined for bar specimens of the same material, using piezoelectric sensors and strain gauges. The comparisons are encouraging. POLYM. COMPOS., 26:542–551, 2005. © 2005 Society of Plastics Engineers