Measurement Of Shear Properties Research Articles

Characterizing dispersion in bovine liver using ARFI-based shear wave rheometry

Background: Dispersion presents both a challenge and a diagnostic opportunity in shear wave elastography (SWE). Shear Wave Rheometry (SWR) is an inversion technique for processing SWE data acquired using an acoustic radiation force impulse (ARFI) excitation. The main advantage of SWR is that it can characterize the shear properties of homogeneous soft media over a wide frequency range. Assumptions associated with SWR include tissue homogeneity, tissue isotropy, and axisymmetry of the ARFI excitation). Objective: Evaluate the validity of the SWR assumptions in ex vivo bovine liver. Approach: SWR was used to measure the shear properties of bovine liver tissue as function of frequency over a large frequency range. Assumptions associated with SWR (tissue homogeneity, tissue isotropy, and axisymmetry of the ARFI excitation) were evaluated through measurements performed at multiple locations and probe orientations. Measurements focused on quantities that would reveal violations of the assumptions. Main results: Measurements of shear properties were obtained over the 25–250 Hz range, and showed a 4-fold increase in shear storage modulus (from 1 to 4 kPa) and over a 10-fold increase in the loss modulus (from 0.2 to 3 kPa) over that decade-wide frequency range. Measurements under different conditions were highly repeatable, and model error was low in all cases. Significance and Conclusion: SWR depends on modeling the ARFI-induced shear wave as a full vector viscoelastic shear wave resulting from an axisymmetric source; it is agnostic to any specific rheological model. Despite this generality, the model makes three main simplifying assumptions. These results show that the modeling assumptions used in SWR are valid in bovine liver over a wide frequency band.

A database of the structural behavior of masonry in shear

This paper reports the results of several on-site investigations carried out by the authors in the last 20 years in central Italy (Umbria, Marche, Emilia and Abruzzo regions) on masonry wall panels. The use of stone and brickwork masonry has been common for centuries not only for rural residences but also for public and religious buildings. In many areas, where the stone was abundant, stone became the material of choice for all constructions. However from rubble stone to perfectly squared stones, the mechanical properties may highly differ. Test results are reported with an accurate survey and analysis of the masonry typology and mechanical characterization was performed according to ASTM standards and consisted of measurements of shear properties. The paper also reports the experimental results of full-scale tests conducted on brickwork walls using different bonding patterns, mortar types and brick dimensions. These data were recorded in terms of shear strength, elastic properties and deformation capacity and are of critical importance for design, reinforcement or retrofit purposes in earthquake-prone areas. All tests were conducted on site from pre-existing undamaged wall panels. Finally, test results are compared with existing standards and indicate that masonry shear strength is sometimes overestimated by the Italian Building Code.

The Application of Modern Powder Characterisation Methods in Product and Process Development of Solid Dosage Forms

The pharmaceutical industry still produces the vast majority of their products, from powdered ingredients, in the form of solid doses. Despite their ubiquity, powders are difficult materials to characterise and understand, as evidenced by the frequent problems encountered during manufacture. The reason for this is their complex rheological behaviour coupled with numerous environmental variations, such as humidity. Equally, the range of processes used to manipulate powders subject them to extremes of stress from high compaction loads seen in compactors to the dispersed state seen in fluidised bed dryers. Thus, it is evident that ensuring that the powders characteristics are compatible with the way they are to be processed is a clear prerequisite for today's Quality by Design driven manufacturing. Modern, computer controlled instrumental techniques, including the dynamic, bulk and shear property measurements have enabled direct measurements of a powders response to aeration, consolidation and flow rate - all at low stresses - as well as quantifying shear and bulk properties (such as density, compressibility and permeability). In order to demonstrate how fully characterising a powder can be used in the design, operation and troubleshooting of processes, this paper will present examples of common pharmaceutical unit operations and the different powder characteristics that most influence the performance of each.

Direct measurement of shear properties of microfibers

As novel fibers with enhanced mechanical properties continue to be synthesized and developed, the ability to easily and accurately characterize these materials becomes increasingly important. Here we present a design for an inexpensive tabletop instrument to measure shear modulus (G) and other longitudinal shear properties of a micrometer-sized monofilament fiber sample, such as nonlinearities and hysteresis. This automated system applies twist to the sample and measures the resulting torque using a sensitive optical detector that tracks a torsion reference. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers, for which G is well known. Two industrially important fibers, IM7 carbon fiber and Kevlar(®) 119, were also characterized with this system and were found to have G = 16.5 ± 2.1 and 2.42 ± 0.32 GPa, respectively.

Shear characterisation of uni-directional fibre reinforced thermoplastic melts by means of torsion

Intra-ply shear appears during the forming process of hot thermoplastic laminates with a uni-directional fibre reinforcement. This paper proposes a torsion bar test to characterise the longitudinal shear mechanism, which can be performed with a standard rheometer. Sensitivity analyses showed that most reliable shear property measurements can be obtained by using torsion bar specimens with a close to square cross section. The method is implemented in practise and critically evaluated. Storage and loss moduli were determined for carbon UD/PEEK specimens at high temperatures. Non-linear material behaviour was found for relatively small shear strains. The linear regime was focussed on subsequently, where the characteristics were found to be similar to that of a visco-elastic solid or weak gel, confirmed by a dominant storage modulus and a weak frequency dependency. Future work is recommended to be focussed on the large strain regime, for which this paper provides a found basis.

Measurement of adhesive shear properties by short beam shear test based on higher order beam theory

This paper refers to the measurement of the shear properties of adhesive bonding by a new beam theory using the short beam shear (SBS) test configuration. A novel higher-order sandwich beam theory has been developed to analyze the adhesive bonded beam that consists of two adhered laminates and a single layer of adhesive in between. The closed form analytical solution for the SBS test model of the adhesively bonded beam is obtained in terms of deflection and stress distribution. The present theory has been used for calculating the adhesive shear modulus from the structural compliance. The initiation of stiffness degradation for the short beam shear test model was used as the critical load value for deriving the adhesive shear strength. A finite element model is built for validating the present model, and to evaluate its suitability for measuring adhesive shear properties. The present theory shows better accuracy for measuring the shear modulus than existing theories for both thin and thick adhesive layers. The measured strength values are more accurate than those obtained from the single lap joint shear test model. This theory can be used for adhesive materials with linear elastic deformation behavior.

Shear properties of wood measured by the asymmetric four-point bending test of notched specimen

Abstract The asymmetric four-point bending test for obtaining shear properties of wood was examined. Rectangular bars with various notches on top and bottom surfaces of western hemlock (Tsuga heterophylla Sarg.) were prepared as a specimen. The shear modulus, proportional limit stress, and shear strength were measured. The influence of notch configuration on the shear properties was examined independently by finite element calculations. The influence of notch configuration was not significant in experiments, while it was found relevant in finite element analyses. Although the pure shear stress condition could not be realized after the initiation of failure, the measurement of shear properties of solid wood simply by the asymmetric four-point bending test was feasible.

A New Specimen Geometry for the Iosipescu Shear Test

Inspired by the notch root axial splits observed in testing unidirectional composites, a new staggered geometry is proposed for the Iosipescu shear test specimen. It will be shown that the new specimen does not suffer from the tensile stress concentrations which seem to be the true cause for axial splits. Also, for the orthotropy ratio examined, the shear stress distribution across the midsection with the new geometry is more uniform than that in the original configuration. As a result, the staggered beam specimen can provide more accurate measurement of shear properties of unidirectional composites.

Measurements of shear characteristics of textile composites

The paper is devoted to experimental study of shear strength and shear modulus of three types of 3D textile composites based on different reinforcing fibres and matrices and made by various technologies, as well as 2D glass fibre/epoxy plastic (GFRP) with lay-up of (±45°). Correct measurement of shear properties of 3D textile composites is a complex problem due to the lack of the planes of weak shear strength and high structural heterogeneity of the materials. These features of 3D textile composites make it problematic to use a set of shear tests developed for unidirectional and laminated composites and forced to call a special attention to the shear tests of isotropic materials. Shear properties of the composites studied are measured by nine different shear tests, including Iosipescu method and its modification, Asymmetric Four-Point Bending (AFPB). It was done by a comparative analysis and evaluation of suitability of the shear tests applied for 3D textile composites and 2D GFRP/Epoxy with lay-up of (±45°).

Theoretical and experimental evaluation of the Iosipescu shear test

Use of the Iosipescu shear test for measurement of shear properties of unidirectional laminae has been studied both analytically and experimentally. The intralaminar shear strength and shear stiffness of glass-reinforced polyester material have been measured using specimens with two different fibre orientations. Acoustic emission has been monitored and a fractographic study carried out. A finite element analysis has been conducted to evaluate the stress distribution within the specimen, assuming isotropic and orthotropic elastic properties of the material. There is a complicated stress distribution in the specimen, particularly in the vicinity of each notch root, depending on the elastic properties of the composite. The shear stress region in the specimen gauge section is almost uniform, though small normal compressive stresses exist. The experimental results have shown that the measured shear modulus does not depend on reinforcement orientation. However, it has been observed that different failure modes occur in each case. This results in a change in apparent shear strength of the composite with fibre orientation. Some explanations of these differences have been found in a detailed analysis of the local stresses at the roots of the notches. It is considered that the presence of tensile stresses in this area is primarily responsible for the apparent reduction in the shear strength.

Measurement of shear properties of fibre composites: Part 1. Evaluation of test methods

Six methods have been evaluated of measuring the shear properties of a fibre composite consisting of a 65-volume % aramid fibre in an epoxy. The shear data obtained from each of the methods was compared with the 90°-wound thin-walled tube torsion test, which was used as the standard. Based on that comparison, it is recommended, for the present, that the ± 45° off-axis laminate tensile shear test be used for determining the shear properties of composites. The method is simple, inexpensive, and reliable, and its shear stress/strain response is the closest to that of the 90° wound thin-walled tube torsion test.

Measurement of shear properties of fibre composites: Part 2. Shear properties of an aramid fibre in several epoxy resins

Shear properties of composites consisting of an aramid fibre (Kevlar 49) impregnated with seven different epoxy resins were measured with the ± 45° off-axis laminate tensile shear test. Experimental results showed that the shear properties of composites made from this fibre varied depending on the epoxy resin used, and that this shear test successfully detected those variations: the shear modulus, failure stress, and shear strain at failure stress varied from 1520 to 1923 MPa, 21.4 to 39.7 MPa, and 1.35 to 2.43%, respectively.

Shear property measurements of adhesives in composite material bonded joints : Renton, W. J. and Vinson, J. R. Conference on Composite Reliability, ASTM STP 580 (American Society for Testing and Materials, 1975) pp 119–132

Shear property measurements of adhesives in composite material bonded joints : Renton, W. J. and Vinson, J. R. Conference on Composite Reliability, ASTM STP 580 (American Society for Testing and Materials, 1975) pp 119–132

Repeated loading and creep effects in shear property measurements on unidirectional cfrp

An experimental evaluation of the effects of repeated loading and creep on the measurement of the shear strength and modulus of unidirectional carbon fibre-reinforced plastics is described. For the epoxy resin systems used the results indicate that repeated loading below about 30% of the ultimate shear stress is unlikely to affect any strength value subsequently recorded. At higher stress levels, however, the creep rate becomes significant, and the specimen must be loaded to failure within a few seconds if initial strength is required.