Search

Indian standard Code-IS:456-2000 and Eurocode EC:02-2004 for the design of the concrete structure is limited to the concrete with compressive strength of 55 MPa and 90 MPa respectively. For defining the stress block parameters and for the design of concrete structures using Very high strength concrete (100 MPa to 150MPa); a well-defined stressstrain behavior becomes necessary, particularly the experimental values for the strain at peak stress and ultimate strain capacity. The presents study attempts to cater to these needs by experimentally evaluating the unconfined stressstrain behavior of nine cylindrical specimens with a compressive strength between 100 MPa to 150 MPa, in a servocontrolled (Strain-controlled) compression testing machine. The strain values recorded at peak stress for 100 MPa and 150 MPa concrete are approximately 3000 microstrains and 3500 microstrains respectively. Compared to normal and high-strength concrete, the rising limb of the curves for VHSC (Very high strength concrete) is much steeper and approaches a straight path, also the strain at peak stress and ultimate strain coincide, depicting a negligible post-peak strain hardening region. LVDT and compressometer gave different strains for the same load and specimen. This signifies the role of the gauge length ratio used in these strain measuring devices. [ABSTRACT FROM AUTHOR]

Measures the separated electrostriction tensor components for single-crystal calcium fluoride by the converse effect, using a specially designed uniaxial stressing jig. Alternative experimental approaches to the measurement of electrostriction; Basic principles of the converse method of measurement; Illustration of the direct current compressometer.

Abstract: In the field of Civil Engineering, the evaluation of concrete elasticity modulus relies heavily on traditional strain gauges like electric resistance strain gauge, demec mechanical strain and compressometer. These strain gauges work pretty well but the sample surface preparation and the strain gauge adhesion are tedious and time-consuming. On the other hand, convenient non-destructive testing methods like rebound hammer and ultrasonic pulse velocity have the disadvantage of large data scattering and low reliability. In this paper, we aim to develop a handy, reliable and cost-effective method for concrete property evaluation based on an optical technique called automatic digital image correlation (ADIC), which acts as an optical strain gauge. By incorporating an automatic searching approach, the proposed ADIC greatly expands the convergence range of normal digital image correlation (DIC) algorithms and is able to automatically determine concrete strain in real time without human interaction. After the optical strain gauge is set up, the axial concrete strain as well as the stress–strain curve is plotted in real time when the concrete sample under testing is loaded. The concrete elasticity modulus is then determined from the curve. A series of experiments have been conducted to evaluate the performance of the proposed optical strain gauge. Comparisons are also carried out between the proposed optical strain gauge and traditional strain gauges such as electronic strain gauge, compressometer and demec mechanical strain gauge, which further confirm the accuracy, convenience and reliability of the proposed technique. [ABSTRACT FROM AUTHOR]

Abstract: Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN system were investigated. The ceramics with a formula (1−x)Pb(Zr1/2Ti1/2)O3–xPb(Zn1/3Nb2/3)O3 or (1−x)PZT–(x)PZN (x =0.1–0.5) were prepared by a conventional mixed-oxide method. The ferroelectric properties under the compressive stress of the PZT–PZN ceramics were observed at the stress levels up to 170MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P sat), the remnant polarization (P r), and the coercive field (E c) decreased. These results were interpreted through the non-180° ferroelastic domain switching processes. [Copyright &y& Elsevier]

Purpose - For size reasons, adapted sensors, able to measure intrinsic mechanical properties of fabrics, have not been developed yet. The study aims at developing a sensor that can be inserted within a specific textile, a "complex" fabric used as seat-cover fabrics, and consisting of an assembly of three layers. Design/methodology/approach - Piezoelectric polymer sensors containing polyvinylidene fluoride (PVDF) were chosen. A total of 20 "complex" were studied. A characterisation in compression was achieved, using the Kawabata Evaluation System. The best-adapted measurement method using a PVDF sensor has been required. The method consists in analyzing the response under compressive stress of a PVDF disc using the resonant frequency of the material. A constraint series is applied to the fabric in the sensor area; the maximal phase at the sensor's resonant frequency is taken up for each one. Findings - Phase variation is linear and differs according to the studied "complex". A correlation study between Kawabata compression parameters and slopes did not show any relationship between slope values and compression properties when the surface fabrics of "complex" are compared, but a classification in "families" is possible when different foams are considered. Research limitations/implications - Further studies should demonstrate whether these "smart" textiles could find applications in the automotive field, to measure accurately the mass of a passenger. The influence of the external parameters (vibrations, temperature variations) has to be checked, knowing that the sensor is not depending on moisture. To complete the study, the sensor has to be tested in a real situation, i.e. inserted in a car-seat, in contact with a human body. Originality/value - This study promises development of a sensor that can be inserted into a specific textile, a "complex" fabric used as a seat-cover, consisting of an assembly of three layers. [ABSTRACT FROM AUTHOR]

Purpose - This paper aims to describe new measuring device designed for measuring the pressure exerted by textile products used in healing therapy of hypertrophic scars. The testing device called "Textilpress" has been used for verification of the usually used method of designing and manufacturing ready-made compression garment products. Design/methodology/approach - The pressure measurement, realized by use of the "Textilpress" device, is an indirect measuring method, which is based on the Laplace Law. The investigations described in this paper concern the pressure measuring under textile bands placed on the models representing selected parts of the human body with pre-set circumferences. For this purpose, rigid cylinders were prepared, covered by a layer of neoprene which simulated the susceptibility of human skin. Findings - The investigations described in this paper indicate that the "Textilpress" test-device may be used for pressure measuring exerted by compression bands on the cylinder surface. In order to estimate the pressure exerted on a particular body part with the shape close to a cylinder, a measurement should be carried out on a cylinder with a circumference similar to that of the selected part of the human body. Research limitations/implications - The "Textilpress" test-device may be used by the manufacturers for measuring pressures exerted by compression bands (manufactured from knitted fabrics) on the cylinder surface of a pre-set diameter. In order to estimate the pressure exerted on a particular body part with the shape close to a cylinder, a measurement should be carried out on a cylinder with a circumference similar to that of the selected part of the human body. Originality/value - As hospitals do not possess appropriate measuring devices, which would enable one to measure the pressure on the scar exerted by the textile garment, the pressure efficiency and the appropriate fittings are estimated subjectively for the particular case. The "Textilpress" device enables monitoring such pressure. [ABSTRACT FROM AUTHOR]

The dielectric constant of lead-based ferroelectric ceramics in three different systems, i.e. BT-PZT, PMN-PT and PMN-PZT, was measured under uniaxial compressive pre-stress to investigate the contributions of different domain-phenomena. The dielectric constant was observed at room temperature under the compressive pre-stress up to 15 MPa, 22 MPa and 5 MPa for BT-PZT, PMN-PT and PMN-PZT, respectively, using a homebuilt uniaxial compressometer. Dielectric constant of the BT-PZT ceramics increased significantly with increasing applied stress. Larger changes in the dielectric constant with the applied stress were observed in the PZT-rich compositions. However, for PMN-PT and PMN-PZT ceramic systems, changes in the dielectric constant with the stress were found to depend significantly on the ceramic compositions. The experimental results could be explained by both intrinsic and extrinsic domain-related mechanisms involving domain wall motions, as well as the de-aging phenomenon from the application of the compressive pre-stress. Roles of different types of domains, i.e. micro-domains and nano-domains, were also discussed. [ABSTRACT FROM AUTHOR]

Effects of an uniaxial compressive pre-stress on the dielectric properties of normal and relaxor ferroelectric ceramic composites in BT-PZT and PMN-PZT systems are investigated. The dielectric properties are observed under the compressive pre-stress levels up to 15 and 5 MPa for BT-PZT and PMN-PZT, respectively, using a uniaxial compressometer. Both the dielectric constant and the dielectric loss tangent of the BT-PZT ceramics increase significantly with increasing applied stress. Larger changes in the dielectric properties with the applied stress are observed in the PZT-rich compositions. For PMN-PZT ceramics, the dielectric constant of the PZT-rich compositions increases slightly, while that of the PMN-rich compositions decreases with increasing applied stress. On the other hand, changes in the dielectric loss tangent with stress are found to be compositional independent. The experimental results are explained with the domain wall motion and de-aging mechanisms from the application of the compressive pre-stress. More importantly, this study undoubtedly shows that the applied stress significantly influences the dielectric properties of both ceramic composite systems. [ABSTRACT FROM AUTHOR]

A simple dynamic instrument for measuring very small stress dependence of capacitance is presented in this article. We describe the design and development of a dynamic compressometer for converse electrostrictive measurements on low dielectric constant materials. This redesigned system is capable of resolving a change in capacitance of 10[SUP-17]F or smaller. The most important feature is the dynamic stressing system incorporated to improve the accuracy and the reproducibility of the measurements. Furthermore, the uniaxiality and uniformity of the applied stress are found to be critical to the measurements. Therefore, a uniaxial stress delivery scheme using ball bearings is employed in the measurements to improve the accuracy of the experimental results. The converse electrostrictive coefficients obtained from this instrument agree reasonably well with those measured directly by a single-beam interferometer. [ABSTRACT FROM AUTHOR]