Katsumi Horiguchi

Electric fracture and polarization switching properties of piezoelectric ceramic PZT studied by the modified small punch test

The fracture behavior of a piezoelectric ceramic under applied electric fields has been discussed through experimental and theoretical characterizations. The modified small punch (MSP) tests were performed on a commercial piezoelectric ceramic. The fracture initiation loads under different electric fields were obtained from the experiment. Fracture surface was examined for the MSP specimens to identify the failure mechanisms under high electric fields. A nonlinear three-dimensional finite element analysis was also employed to calculate the fracture deflection and MSP energy. A procedure is presented for determining the fracture and polarization switching properties due to electrical effects by experimental and theoretical means.

Double Cantilever Beam Measurement and Finite Element Analysis of Cryogenic Mode I Interlaminar Fracture Toughness of Glass-Cloth/Epoxy Laminates

An experimental and analytical investigation in cryogenic Mode I interlaminar fracture behavior and toughness of SL-E woven glass-epoxy laminates was conducted. Double cantilever beam (DCB) tests were performed at room temperature (R.T.), liquid nitrogen temperature (77 K), and liquid helium temperature (4 K) to evaluate the effect of temperature and geometrical variations on the interlaminar fracture toughness. The fracture surfaces were examined by scanning electron microscopy to verify the fracture mechanisms. A finite element model was used to perform the delamination crack analysis. Critical load levels and the geometric and material properties of the test specimens were input data for the analysis which evaluated the Mode I energy release rate at the onset of delamination crack propagation. The results of the finite element analysis are utilized to supplement the experimental data.

Analysis and Testing of Indentation Fracture Behavior of Piezoelectric Ceramics Under an Electric Field

To estimate the electric fracture toughness, indentation fracture (IF) tests were made on piezoelectric materials under combined mechanical and electrical loads. Lead zirconate titanate (PZT) ceramics from a commercial source were used. A three-dimensional finite element analysis was also employed to calculate the energy release rate and stress intensity factor. Surface cracks produced by indentation with Vickers indented were modeled as two point-force loaded half-penny-shaped cracks.

Analytical and Experimental Studies of Short-Beam Interlaminar Shear Strength of G-10CR Glass-Cloth/Epoxy Laminates at Cryogenic Temperatures

Cryogenic interlaminar beam tests in the form of three-point flexure are examined both experimentally and analytically. The use of the short-beam shear test for measuring the interlaminar shear strength of glass-cloth/epoxy laminates at low temperatures is evaluated first. The interlaminar shear tests were carried out with short-beam shear specimens at room temperature, 77 K and 4 K to evaluate the interlaminar shear strength of G-10CR glass-cloth/epoxy laminates. Each specimen was placed on two roller supports that allow lateral motion and a load was applied directly at the center of the specimen. These tests were conducted in accordance with ASTM, 1984, Standard Test Method for Apparent Interlaminar Shear Strength of Parallel Fiber Composites by Short-Beam Method, Designation D2344-84. The effects of temperature, specimen width, and span-to-thickness ratio on the apparent interlaminar shear strength are shown graphically. Photomicrographs (scanning electron micrographs, optical micrographs) of actual failure modes were utilized to verify the failure mechanisms. A three-dimensional finite element analysis was also performed to investigate the effects of specimen width and span-to-thickness ratio on the shear stress distribution in the mid-plane. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. The numerical findings are then correlated with the experimental results.

Analysis and Testing of Mixed-Mode Interlaminar Fracture Behavior of Glass-Cloth∕Epoxy Laminates at Cryogenic Temperatures

This paper presents results from an analytical and experimental study of the effect of temperature and mixed-mode ratio on the interlaminar fracture toughness in glass-cloth/ epoxy laminates. Mode I, mode II, and mixed-mode tests were conducted by the double-cantilever beam, end-notched flexure, and mixed-mode bending lest methods at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). A finite element model was used to perform the delamination crack analysis. Mode I, mode II, and mixed-mode energy release rates at the onset of delamination crack propagation were computed using the virtual crack closure technique. The fracture surfaces were examined by scanning electron microscopy to correlate with the interlaminar fracture properties.

Theoretical and Experimental Evaluation of Double-Notch Shear Strength of G-10CR Glass-Cloth/Epoxy Laminates at Cryogenic Temperatures

the cryogenic interlaminar shear behavior of G-10CR glass-cloth/epoxy laminates has been discussed through theoretical and experimental characterizations. The use of the double-notch shear test for measuring the interlaminar shear strength of glass-cloth/epoxy laminates at low temperatures is evaluated first. The interlaminar shear tests were carried out with double-notch shear specimens at room temperature, 77 K and 4 K to evaluate the interlaminar shear strength (ILSS) of G-10CR glass-cloth/epoxy laminates. The double-notch shear specimen was loaded on its ends in compression with a supporting jig to prevent buckling. These tests were conducted in accordance with ASTM D3846-79. The effects of temperature, specimen thickness, and notch separation on the apparent ILSS are shown graphically. Fracture surfaces were examined by scanning electron microscopy (SEM) and optical microscopy to verify the failure mechanisms. A three-dimensional finite element analysis was also performed to investigate the effect of specimen thickness and notch separation on the shear stress distribution in the expected fracture plane. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. The numerical findings are then correlated with the experimental results. The validity of this test technique has been established.

End-notched flexure testing and analysis of Mode II interlaminar fracture behavior of glass-cloth/epoxy laminates at cryogenic temperatures

This paper presents results from an analytical and experimental study of the effect of temperature and geometrical variations on the Mode II interlaminar fracture toughness in glass-cloth/epoxy laminates. The end-notched flexure (ENF) test geometry was used for Mode II experiments, which were performed at room temperature (R.T.), liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). The fracture surfaces were also examined by scanning electron microscopy to verify the fracture mechanisms. A finite element model was further used to perform the delamination crack analysis. Critical load levels, and the geometric and material properties of the test specimens were input data for the analysis, which evaluated the Mode II energy release rate at onset of delamination crack propagation. The results of the finite element analysis are used to supplement the experimental data.

Experimental and Finite-Element Analysis of Woven Glass-Cloth/Epoxy Laminate Tensile Specimen at Room and Low Temperatures

ABSTRACT To evaluate the tensile properties of SL-ES30 glass-cloth/epoxy laminates for superconducting magnets in fusion energy systems, tensile tests were examined both experimentally and analytically. The tensile tests were conducted in accordance with JIS K 7054 at room temperature and liquid nitrogen temperature (77 K). The general specimen geometry was a rectangular dog-bone shape with constant gage length but with each specimen size having a different specimen width. The experimental finding provides the data for analytical modeling. The model utilizes two damage variables that are determined from experimental data. A finite-element method coupled with damage was adopted for the extensional analysis. The effects of temperature, specimen geometry, and gripping method on the tensile properties are examined.

Electroelastic field concentration by circular electrodes in piezoelectric ceramics

The electroelastic field concentration due to circular electrodes in piezoelectric ceramics has been discussed through theoretical, numerical and experimental characterizations. This paper consists of two parts. In the first part, the problem of a surface electrode attached to a semi-infinite piezoelectric solid was formulated by means of Hankel transforms and the solution was solved exactly. The displacements and electric potential were expressed in closed form. In the second part, finite element analysis was carried out to study electroelastic fields in piezoelectric disks containing circular electrodes of different radii by introducing a model for polarization switching in local areas of electroelastic field concentration. A nonlinear behavior induced by localized polarization switching was observed between the strain and the voltage applied to the electrode. Experiments were also conducted to study the strain state near the electrode tip. Comparison of the predictions by the present model with experimental data is conducted and pertinent conclusions are drawn. This work is the first attempt to obtain nonlinear electroelastic fields around a circular electrode in piezoelectric ceramics and validate the polarization switching model.

Compression behavior of glass-cloth/epoxy laminates at cryogenic temperatures

In order to evaluate the cryogenic compressive properties of G-10CR and SL-ES30 glass-cloth/epoxy laminates for superconducting magnets in fusion energy systems, compression tests were performed at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). The effects of temperature and specimen geometry on the compressive properties are examined. Photomicrographs of actual failure modes were utilized to verify the failure mechanisms.