Glass-epoxy Laminates Research Articles

ＤＣＢ試験および有限要素法による織物ガラス‐エポキシ積層材料の極低温モードＩ層間破壊靭性

The cryogenic interlaminar fracture toughness of woven glass-epoxy laminates was measured under mode I loading using double cantilever beam (DCB) tests. The tests were performed at room temperature (R. T.), liquid nitrogen temperature (77K) and liquid helium temperature (4K) to evaluate the effect of temperature and geometrical variations on interlaminar fracture toughness. The fracture surfaces were examined by scanning electron microscopy to verify the failure mechanisms. A finite element model was used to perform the delamination crack analysis. The results of the finite element analysis are utilized to supplement the experimental data.

The effect of strain rate and fibre content on the Poisson’s ratio of glass/epoxy composites

The utilisation of composite materials in structural applications has prompted the need for a full characterisation of their behaviour under dynamic loading conditions. The strain rate effects of most unfilled polymers can be described by the Eyring theory of viscosity which assumes that the deformation of a polymer involves the motion of a chain molecule over potential energy barriers. The Eyring model suggests that yield stress varies linearly with the logarithm of strain rate. In the present study, tensile tests were performed on a glass epoxy laminate at different rates of strain to determine the effects of strain rate on the Poisson’s ratio of the material. In addition, further tests were conducted at varying fibre contents to verify the relationship between fibre content and Poisson’s ratio. The findings from the experimental results suggest that Poisson’s ratio is not sensitive to strain rate. In addition, it was suggested that the absence of rate sensitivity in the Poisson’s ratio of the laminates tested is due to the presence of fibres in the composites.

Characterization and evaluation of piezoelectric composite bimorphs forin-situ acoustic emission sensors

Mixed connectivity composites consisting of a ferroelectric ceramic powder of calcium modified lead titanate dispersed in a polymer matrix have been fabricated into piezoelectric bimorph sensors. The piezoelectric, dielectric and electromechanical coupling coefficients of these sensors have been measured and a full characterization of the electromechanical properties are reported. The suitability of these bimorph transducers as in-situ acoustic emission sensors, embedded into glass-epoxy laminate plate like structures, has been investigated. A comparison of the performance of these sensors to those of previously investigated monomorph sensors fabricated from the same material has been made.

織物ガラス‐エポキシ積層材料の極低温圧縮特性

In order to evaluate the cryogenic compressive properties of G-10CR and SL-ES30 woven glass-epoxy laminates for superconducting magnets in fusion energy systems, compression tests were performed at room temperature (R. T.), liquid nitrogen temperature (77K) and liquid helium temperature (4K). These tests were conducted in accordance with JIS K 6911 and JIS K 7056. Compression specimens of G-10CR with different specimen length to cross-sectional area ratios were tested in the normal direction (normal to the glass cloth). Compression specimens of SL-ES30 with different specimen length to cross-sectional area ratios were also tested in the warp, fill and normal directions. The effects of temperature and specimen geometry on the compressive properties were examined. Photomicrographs of actual failure modes were utilized to verify the failure mechanisms.

極低温における織物ガラス-エポキシ積層材料G-11の損傷・破壊力学解析

We discuss the cryogenic damage and fracture behaviors of G-11 woven glass-epoxy laminates. In conjunction with the cryogenic fracture toughness test, a two-dimensional finite element analysis was conducted to predict the fracture and deformation for models of the compact tension specimens. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. Hoffman’s criterion was selected as the criterion for damage accumulation induced by fiber breakage and matrix cracking was detected by the maximum strain criterion. The strain energy method was adopted to calculate strain energy release rate which leads to determination of stress intensity factor. In order to verify the model, correlations between experimental and analytical results were made, in terms of the load-displacement response and the extent of damage growth. At room temperature and 77 K, good agreements were found between the calculations and the experimental data. The predictions showed that the fracture behavior was influenced by temperature rises associated with individual damage events at 4 K. An apparent fracture toughness, Ki, was calculated for each specimen using the load, Pi, at which a significant change of slope in the damage zone size versus load curve was observed. The Ki value was independent of notch length but increased with specimen size.

Location and Geometry of Defects in Composite Laminates from Infrared Images

An infrared scanning system is employed to analyze defective glass-epoxy laminates. Several specimens, manufactured with insertion of pieces of different materials to simulate either delaminations or inclusions are considered, and tests are performed for varying material, shape, depth, and size of inserts. Each specimen is heated by quartz lamps and viewed by an infrared camera, and thermograms are acquired in time sequence in the transient heating phase. Thermograms are quantitatively analyzed in terms of time temperature profiles along lines through the center of defects. The center of a defect is individuated with high certainty; the size instead is measured (from the temperature profile) much well as much as the defect is positioned at small depth and is large. For each test condition, the measured dimension is related to the real one. This ratio, plotted against time, shows an asymptotic distribution and allows for a simple evaluation of defective laminates.

Energy dissipation and temperature rise associated with crack extension in a woven glass-epoxy laminate at low temperatures

Failures, fracture (cracking) and debonding of filler materials used in the winding of a high-performance superconducting magnet generate heat. When combined with the high thermal response of the materials at low temperatures, the small heat input may result in premature quenching of the magnet. An analytical procedure, using a finite element method, was developed to calculate the dissipative energy and temperature rise associated with crack extension in a woven glass-epoxy laminate(G-10) at low temperatures. The amount of energy dissipated during partial fracture of the test specimen is calculated as a function of crack speed using a dynamic strain energy release rate. The dissipative energy is compared with the heat output determined experimentally at 77 K, and the conversion rate of dissipative energy into heat is obtained. From the average value for the conversion rate, the heat outputs at 77 K for total fracture and at 4 K for partial fracture are predicted. Temperature elevations at the crack tip are also calculated.

Singular stresses of cracked woven glass-epoxy laminates at cryogenic temperatures

We consider the singular stresses of woven glass-epoxy laminates with a parallel array of transverse cracks and temperature-dependent properties at cryogenic temperatures under tension. A generalized plane strain finite element model is used to study the influence of warp angle on the cryogenic fracture behavior of two-layered woven laminates. Special elements with exact stress singularity are placed around the crack tip. Numerical calculations are carried out, and the stress intensity factor at different temperatures is shown graphically.

77 Kにおける織物ガラス-エポキシ積層材料G-11の破壊特性および寸法効果

77 Kにおける織物ガラス-エポキシ積層材料G-11の破壊特性および寸法効果

Delamination Initiation Around Cut Holes in Symmetric Laminates: Effects of PET Film Interleaving

The effects of PET film interleaving on delamination initiation in centrally notched (±θ/0)s composite laminates with fiber directions θ = 15°, 30°, 45° and 60° respectively have been investigated. A pair of interleaves were selectively placed at delamination prone interfaces in each laminate. The circular holes were cut in glass-epoxy laminates using high-speed drilling (HSD) and abrasive waterjet cutting (AWC) in order to compare the influence of hole surface finish with interleaving. Surface profilometry was used as a nondestructive technique for detecting delamination onset during tensile testing. It was found that although HSD interleaved holes were the roughest, the delamination onset stresses were significantly increased particularly for 30° < θ < 60°. For ±θ = 60°, however, delamination onset was unaffected by either hole surface finish or interleaving.

Impact Studies in Glass Epoxy Laminates Containing Foam

E glass epoxy laminates were made by a hand layup process. Laminates containing the central portion having either a 2 layer larger cell sized thicker width or a 3 layer thinner width flexible foam were also fabricated by the same route using a room temperature curing resin. Test coupons were cut from the fabricated laminates and impacted by a pendulum, having facility to load specific values for its mass, on the face of the laminate. Impacts were made by a single mass or a two stage impact operations involving preliminary hits, first by a smaller mass and then by a larger mass. The energy values associated with the process were computed. Macroscopy on failed test coupons was done to identify the dominant mode of failure and correlate the mechanical test data with failure processes. It is seen that foam bearing materials absorb increased impact energy compared to plain laminates and further, the cell-size/interfacial area of the foam plays a significant role in altering the fracture phenomena.

Repeated drop weight impacts and post-impact ILSS tests on glass-epoxy composite

E glass epoxy laminates of thicknesses in the range 2–5 mm were subjected to repeated impacts. For each thickness the number of hits to cause tup penetration was determined and the value of this number was higher the larger the thickness of the laminate tested. The C-scan, before and after impact, was done to obtain information regarding flaw distribution. Short beam shear test samples were made from locations at fixed distances from impact point and tested. The samples closer to the zone of impact showed lower strength values. Scanning fractography revealed shear deformation features for these samples and brittle fracture features for the region near the zone of impact.

織物ガラス‐エポキシ積層材料Ｇ‐１０の極低温破壊及び発熱・温度上昇

In order to evaluate the cryogenic fracture toughness and the temperature rise of G-10 woven glass-epoxy laminates, plane-strain fracture toughness testing was performed with 0.4T compact tension specimens at room temperature, 77K and 4K. Testing was conducted in accordance with ASTM standard E399-83 and JSME standard S001 for determining the fracture toughness. Chromel-vs-Au/0.07% Fe thermocouples were used to measure the temperature rise near the crack tip. The effects of temperature, crack length and crosshead speed on the fracture toughness are examined. The damage morphology around the crack tip of tested specimens was characterized using scanning electron microscopy (SEM).

Edge and interlaminar stresses of glass-cloth-reinforced epoxy laminates under uniform axial extension at cryogenic temperatures

We considered the free-edge and interlaminar stress states of G-10CR woven glass-epoxy laminates under uniform axial extension with temperature-dependent properties. The damage, in general, occurred in the interior of G-10CR glass-epoxy laminates. A finite element method was used to study the influence of weave geometry and cryogenic temperatures on the edge and interlaminar stresses of two-layer woven laminates under uniform axial strain. Numerical calculations are carried out and the stress distributions along the free edge and midplane of the woven laminates are shown graphically for various values of the temperature Φ and warp angle θ. The stress distributions of woven and nonwoven laminates are also compared. Finite element results demonstrated that the weave geometry reduced edge stresses, and the tendency was more pronounced with increasing θ. The large debonding stress tended to increase with increasing θ and decreasing Φ.

Microscopy of impact damage in particulate-filled glass-epoxy laminates

Low-energy impact damage was induced in particulate-filled glass-epoxy laminates by means of a falling weight device, and the damage features were studied by sectioning through the impacted area. The polished sections were studied by optical and scanning electron microscopy to obtain comparative qualitative information about the effects of several different mineral fillers: solid glass beads, hollow glass microspheres, quartz, alumina trihydrate and mica. Approximately 8.5 mm thick laminates, with and without fillers, were impacted at various energies up to 43 J. At the lower impact-energy levels, the damage in the unfilled laminates in most samples was typically transverse matrix cracking, at some distance below the point of impact. Transverse and interlaminar cracking was more extensive in filled than in unfilled laminates. The type and distribution of the damage features are discussed in terms of the properties of the filler particles, and of the stress distributions involved.

Compressive Strength Retention of Impact-Damaged Laminates Containing Particulate Fillers

The effect of six particulate fillers on the compressive strength of undamaged and damaged glass-epoxy laminates was studied. The intention was to determine whether, and how, the mechanical properties of the filled organic matrix could be correlated with the impact damage tolerance (expressed as compressive strength retention after impact) of fitted epoxy-glass laminates. Impact damage was induced by an instrumented falling weight device. The laminates contained solid glass beads, hollow glass microspheres, quartz, calcium carbonate, alumina trihydrate (ATH) and mica. The test results showed that all the fillers, apart from hollow glass microspheres, increased the tensile and flexural moduli of the fitted epoxy, and this in turn was accompanied by an improvement in the compressive strength of some of the undamaged lominates, but there was no positive correlation between the flexural modulus of the fitted matrix and the impact damage tolerance as reflected in compressive strength retention. In contrast there was a good correlation with matrix strength; i.e. a significant decrease in the compressive strength retention of impact-damaged laminates as the matrix flexural strengths were reduced by adding fillers. The pre-impact interlaminar shear strength of the laminates also correlated well with the compressive strength retention after impact.

Compressive Strength Retention of Impact-Damaged Laminates Containing Particulate Fillers

The effect of six particulate fillers on the compressive strength of undamaged and damaged glass-epoxy laminates was studied. The intention was to determine whether, and how, the mechanical properties of the filled organic matrix could be correlated with the impact damage tolerance (expressed as compressive strength retention after impact) of fitted epoxy-glass laminates. Impact damage was induced by an instrumented falling weight device. The laminates contained solid glass beads, hollow glass microspheres, quartz, calcium carbonate, alumina trihydrate (ATH) and mica. The test results showed that all the fillers, apart from hollow glass microspheres, increased the tensile and flexural moduli of the fitted epoxy, and this in turn was accompanied by an improvement in the compressive strength of some of the undamaged lominates, but there was no positive correlation between the flexural modulus of the fitted matrix and the impact damage tolerance as reflected in compressive strength retention. In contrast there was a good correlation with matrix strength; i.e. a significant decrease in the compressive strength retention of impact-damaged laminates as the matrix flexural strengths were reduced by adding fillers. The pre-impact interlaminar shear strength of the laminates also correlated well with the compressive strength retention after impact.

Singular stresses of glass fibre reinforced plastics with a broken layer at low temperatures

In this paper we consider the singular stresses of G-10CR glass-epoxy laminates with a broken layer under tension at low temperatures. The composite material is assumed to be in generalized plane strain. Fourier transforms are used to formulate the problem in terms of a singular integral equation. The order of stress singularity around the tip of the crack which is normal to and ends at the interface between orthotropic elastic materials is obtained. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Numerical results on the stress intensity factor and the order of stress singularity at different temperatures are obtained and are presented in a graphical form.

極低温に冷却される織物ガラス‐エポキシ積層材料の熱衝撃応答

In this paper, we consider the transient thermal-mechanical stress ploblem of cracked woven glass-epoxy laminates with temperature-dependent properties. The woven composite is suddenly cooled at the surfaces. The composite material in generalized plane strain is assumed. Finite element method is used to study the influence of weave curvature and crack formation on the thermal shock behavior of G-10CR glass-epoxy laminates at low temperatures. Numerical results on the transient temperature and thermal-mechanical stress distributions are obtained and are presented in a graphical form.

Properties of laminate composites reinforced with glass fabrics treated with sol-gel transition silicate gel

Glass fabric was treated with sol-gel transition silicate gel to modify the composite interface. Micro roughness on the surface of the glass fabric was observed clearly by the atomic force microscope (AFM) at the surface of glass fabric which had been treated with a base catalytic silicate gel (b-SGSi). The specific surface area of this glass was 1.4 times that of the original glass fabric. The double cantilever beam (DCB) test was carried out on glass epoxy laminate composites, using b-SGSi glass fabrics and standard glass fabrics. In this test, the former laminate showed two fracture modes, stable and unstable crack growth, whereas the latter laminate showed only stable crack growth. In reference to the fracture toughness of the stable crack growth, the former laminate is about 1.4 times greater than that of the latter laminate. It was suspected that the difference was caused by the different interface bonding strength in the composite. The interfacial bonding was also tested by the soldering iron test ...