OS0417 極低温における織物ガラス繊維強化ポリマーコンポジットのモードII疲労はく離進展メカニズム(先端材料システムの力学とメゾスケールモデリング,オーガナイズドセッション)

[Abstract] The objective of this work is to investigate the interlaminar fracture and damage behavior of woven glass fiber reinforced polymer (GFRP) laminates for mixed-mode bending (MMB) configuration at cryogenic temperatures. The crack length corresponding to critical load is determined using measured specimen compliance of the damage states via finite element analysis (FEA), and the critical mixed-mode energy release rates of MMB specimen at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K) are calculated. The values of the critical energy release rate (mixed-mode interlaminar fracture toughness) obtained from the beam theory and FEA are then compared. A FEA coupled with damage is also employed to study the damage distributions within the MMB specimen. Moreover, the results for the special cases of pure mode I and mode II loading of woven GFRP laminates are presented.

Laminated fiber reinforced polymers (FRP) have excellent in-plane stiffness and strength, but suffer from transverse impact loading due to the lack of fiber reinforcement in that direction. Under transverse impact, extensive delamination can occur in the interlaminar resin-rich regions, which leads to a reduction of stiffness and strength. Therefore, many researchers have attempted to establish a standard testing method that characterizes the interlaminar fracture toughness for delamination [1]. In addition to the measurement of the delamination toughness, analysis of the fracture surface using optical microscopy or scanning electron microscopy (SEM) can also provide useful information for the delamination resistance characterization. Recently, we have evaluated mechanical properties of two glass-fiber-reinforced polymers (GFRP) [2], using transverse impact, double cantilever beam (DCB) and end-notched flexure (ENF) tests. Results from the transverse impact and DCB tests showed a clear difference in delamination resistance between the two GFRP, but such a difference was not found from the ENF test. Based on the ENF test results, the two GFRP should have similar delamination resistance in the shear mode (Mode II). Although this discrepancy in delamination resistance may be caused by the toughness variation in different modes of loading, we believe that the discrepancy is mainly due to a problem with the ENF test for the characterization of the delamination resistance. This issue has been raised in several studies [3, 4], and is further investigated here through the examination of fracture surfaces to provide additional evidence. Two GFRP used in this study have polymer matrices that are the same as those used previously, that is, isophthalic polyester (TMR300 isopolyester, provided by Viking Plastics, Edmonton) and polyurethane-based resin (PUL-G polyurethane, provided by Resin System Inc., Edmonton). The PUL-G polyurethane resin contains 15% CaCO3 particulates for stiffness enhancement. For convenience, the two GFRP will be named PI-GFRP and PU-GFRP in this paper, for isopolyesterbased GFRP and polyurethane-based GFRP, respectively. The glass fiber used is 9-oz/yd2 warp, unidirectional woven fabric (provided by ZCL Composites, Edmonton) which consists of parallel fiber bundles stitched together with a gap of around 1 mm. The gap between the fiber bundles generated resin-rich zones in the GFRP. Therefore, the GFRP have resin-rich zones in the intra-laminar, inter-fiber-bundle regions and the interlaminar regions. GFRP plates of nominally 6.0 mm thick were fabricated using a resin transfer molding (RTM) technique. The fiber lay-up of the transverse impact specimens is [(0/90)5]s, and that of the DCB and ENF specimens is [(0/90)402]s of which the four central 0-degree layers were to provide a uni-directional fiber environment in the direction of crack growth, in accordance with most of the test coupons used in the past. The specimens for DCB and ENF tests contain an aluminum insert film, 15 μm thick, that is placed between the 2nd and the 3rd of the four central layers, acting as a starting defect for delamination crack growth. Dimensions of the specimens are 93 × 93 mm2 for the transverse impact test, and 120 × 20 mm2 for the DCB and ENF tests. Overall fiber volume fraction of the specimens is around 40%, estimated using the following equation [5]:

In ITER, superconducting magnets should be used in such severe environment as high fluence of fast neutron, cryogenic temperature and large electromagnetic forces. Insulating material is one of the most sensitive component to radiation. So radiation resistance on mechanical properties at cryogenic temperature are required for insulating material. The purpose of this study is to evaluate irradiation effect of insulating material at cryogenic temperature by gamma-ray irradiation. Firstly, glass fiber reinforced plastic (GFRP) and hybrid composite were prepared. After irradiation at room temperature (RT) or liquid nitrogen temperature (LNT, 77 K), interlaminar shear strength (ILSS) and glass-transition temperature (Tg) measurement were conducted. It was shown that insulating materials irradiated at room temperature were much degraded than those at cryogenic temperature.

Mechanics of chip, delamination, and burr formation in drilling supported woven GFRP composites

Interstitial halogen centers in X-irradiated CsBr

Mode II fracture toughness of glass–epoxy laminated composites under various heating conditions and strain rates

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.

In a context of many studies addressing delamination growth in laminated composites, this thesis provides understanding of the underlying physics of this phenomenon. The models currently used to assess delamination growth are phenomenological in nature and rely almost solely on curve fittings and experimental data. These empirical models are used to predict delamination growth rather than aid in understanding it. This lack of knowledge on the physics of delaminations causes problems for both academia and industry. From the perspective of academia, science needs to be built upon fundamental understanding. However, this is currently not the case for delamination growth. Phenomenological trends, for which the reasons are not yet clear, are assumed as fact, and science tries to advance building on these trends. Meanwhile, from the perspective of industry, engineers compensate for the lack of fundamental understanding with conservativeness, overdesign and a great amount of tests, yielding extra costs. Therefore, the present thesis seeks to understand the fundamentals of delamination growth by physically characterising it. This characterisation is performed relating the strain energy dissipated in delamination growth with the delamination growth rate and the damage mechanisms encountered on the fracture surfaces. To this aim, carbon-epoxy unidirectional laminated specimens were manufactured and tested under mode II and mixed-mode static and fatigue loading. Fracture surfaces were analysed on a Scanning Electron Microscope, and the damage mechanisms were identified and correlated to the strain energy dissipated...

Fatigue life reduction of GFRP composites due to delamination associated with the introduction of functional discontinuities

Glass Fiber Reinforced Polymer (GFRP) soil nailing is great different from steel bar soil nailing in mechanical parameters and the properties. According to a excavation engineering supported by soil nailing, the support structure of soil nailing was simulated by finite element method. By analyzing the displacement, the force, the plastic area and other aspects in sensitive position, the results show that two types of soil nailing can ensure the stability of the slope under the same arrangement. The maximum displacement of GFRP soil nailing on control points of the slope is more 7% to 10% than steel bar soil nailings. Plastic zone of GFRP soil nailing support structures are more obvious in the range and the extent. The arrangement of GFRP soil nailing had been optimized by finite element software, the distance 1.6~1.8m between soil nailings is more appropriate for support structure.

In the present work, the effect of hygrothermal aging on the glass fibre and epoxy matrix interface has been investigated by destructive and non-destructive techniques. The glass fiber reinforced polymer (GFRP) composite laminates were prepared using Vacuum Assisted Resin Infusion Molding (VARIM) technique and the specimens were immersed in simulated seawater, followed by quantitative measurement. Besides this, the tensile tests of GFRP specimens revealed a general decrease in the properties with increasing aging time. Also, exposed specimens were characterized by a non-destructive ultrasonic guided Lamb wave propagation technique. The experimental results demonstrate a correlation between the drop in ultrasonic voltage amplitude and fall in tensile strength with increasing time of immersion. Hence, the comparison of the transmitted guided wave signal of healthy vis-a-vis specimens subjected to different extents of hygrothermal aging facilitated performance evaluation of GFRP composites.

Advanced composite materials have been commonly used in aerospace engineering, because of their good mechanical properties and attractive potential for creating lightweight structures. Susceptibility to delamination is one of the most important issues in the applications of these materials. This disadvantage can prohibit the application of composite materials in primary aerospace structures and limit their lightweight potential. Therefore, characterizing fatigue delamination growth behavior in composite laminates is important for the applications of these materials in aerospace, as it provides the necessary information for the damage tolerance design philosophy. Fibre bridging is an important shielding mechanism during delamination growth in composite laminates. It can increase the fracture toughness by restraining the crack opening and inhibit delamination growth. However, there is no reliable method to take into account of its contribution to fatigue delamination growth. Thus, investigation of this phenomenon and development of a prediction method is required. The objective of this investigation is to study mode I fatigue delamination growth with fibre bridging in composite laminates and provide physics-based interpretations of fatigue delamination growth. Two approaches are applied to interpret the fatigue delamination growth behavior according to different perspectives. In the engineering perspective, the Paris relation is applied. However, in the physics-based perspective, energy principles are used. The bridging effect on fatigue delamination growth is first investigated by a series of fatigue tests. The Paris relation is used to interpret the fatigue data. It demonstrates that fibre bridging can significantly decrease the fatigue crack growth rate, making it invalid to use a single fatigue resistance curve to determine fatigue delamination with bridging. A new method, still based on the Paris relation, is developed to predict fatigue delamination growth with fibre bridging, by correlating the curve fitting parameters with the amount of bridging fibres. Fatigue delamination growth is physically explained according to the energy conservation law. It is found that bridging fibres periodically store and release strain energy upon loading and unloading cycles. However, they have no contribution to the real strain energy release, unless the bridging fibre pullout or fails. This can lead to the invalidity of using the strain energy release rate (SERR) determined by the fixed grip assumption for quasi-static crack growth to interpret fatigue crack growth. Therefore, the SERR commonly used is not a suitable similitude parameter to determine fatigue delamination growth. Energy principles are subsequently used to interpret the stress ratio effect in fatigue delamination growth. A concept of fatigue fracture toughness is proposed to describe the steady fatigue delamination growth, in which little or no bridging fibre pullout or failure occurs. Therefore, all energy dissipation in the steady delamination growth is concentrated on the new crack generation. The fatigue fracture toughness is observed to be interface configuration independent but significantly stress ratio dependent. The mechanisms related to this are interpreted by fractographic observation. Using the concept of fatigue fracture toughness, the stress ratio effect on fatigue delamination growth can be explained with a clear physical background.

This article summarizes the current status of the characterization methods for the strength properties of woven composites at cryogenic temperatures. The double‐notch and short‐beam shear test methods are examined for evaluation of the cryogenic interlaminar shear strength of woven glass fiber‐reinforced polymer (GFRP) laminates. Tensile tests on various unnotched specimens are also discussed based on the results for the cryogenic tensile strength of woven GFRP laminates. In addition, a combined numerical‐experimental method using the open‐hole tensile test and finite element analysis was proposed to evaluate the composite tensile strength at cryogenic temperatures.

Study on interlaminar performance of CNTs/epoxy film enhanced GFRP under low-temperature cycle

Extraordinary strength and ductility of cold-rolled 304L stainless steel at cryogenic temperature