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Our developed accelerated testing methodology (ATM) based on the matrix resin viscoelasticity for the failure life prediction of carbon-fiber reinforced polymers (CFRP) was applied for statistical prediction of long-term fatigue failure life under bending load for the longitudinal direction of unidirectional CFRP laminates, which is an important basic aspect of design for the durability of CFRP structures used for aircraft and other applications. First, the formulations for fatigue life prediction of FRP under cyclic loading are introduced. Second, the time-dependent and temperature-dependent viscoelasticity of matrix resin and the statistical flexural static strengths of CFRP laminates at various temperatures are introduced as the basic data of failure life prediction of CFRP laminates. Third, fatigue bending tests for CFRP laminates are performed at various load levels with various frequencies and temperatures. A master curve of non-dimensional fatigue strength versus number of cycles to failure (S-N master curve) is constructed by substituting data of the second and third steps into the formulations. Finally, the long-term fatigue strength data obtained under cyclic bending load for unidirectional CFRP laminates are compared with the long-term creep strength obtained in the previous paper.

Our developed accelerated testing methodology (ATM) based on matrix resin viscoelasticity for the long-term life prediction of carbon fiber reinforced plastics (CFRP) was applied to assess the statistical prediction of long-term creep failure time of a carbon fiber/polypropylene unidirectional (CF/PP) laminates under creep bending load. Results show that the statistical long-term creep failure times under an arbitrary constant bending load and temperature for the CF/PP laminates can be easily predicted from the statistical static strengths of the CF/PP laminates measured at several temperatures and the viscoelasticity of matrix PP.

Our developed accelerated testing methodology (ATM) based on the matrix resin viscoelasticity for the creep and fatigue failure life prediction of fiber reinforced polymers (FRP) was applied to the statistical prediction of long-term creep failure life for the longitudinal bending of unidirectional Carbon fiber reinforced plastic (CFRP) laminates which is an important basic item for the durability design of CFRP structures used for aircraft and others. As results, the statistical creep failure times measured under several constant bending loads at an arbitrary temperature for unidirectional CFRP laminates were agreed with the predicted results obtained by substituting the matrix resin viscoelasticity and the flexural static strengths of CFRP laminates statistically and easily measured at various temperatures into the formulation of ATM. The long-term creep strength under bending load at an arbitrary temperature predicted were compared with that under tension load obtained by our previous paper. It was clear that the creep strength under bending load degreases drastically with increase in time and temperature comparing with that under tension load; therefore, the effect of time and temperature on the creep failure life under bending load is larger than that under tension load.

Carbon fiber reinforced plastics (CFRP) with the matrix of thermoplastic resin called as carbon fiber reinforced thermoplastics (CFRTPs) has been widely used in the industrial fields. Recently, a thermoplastic epoxy resin (TP-EP resin) has been developed as the matrix of CFRTP and carbon fiber reinforced TP-EP strands (CF/TP strands) molded by pultrusion method began to be used as tension rods for infrastructure under water absorption. On the other hand, an accelerated testing methodology (ATM) for predicting statistically long-term creep and fatigue strengths of CFRP was established by the authors. This study examines the prediction of statistical life time for these developed CF/TP strands at creep and fatigue tension loadings under the wet condition of water absorption with comparison to similar prediction under a dry condition by using our developed ATM. First, the static, creep, and fatigue tensile strengths of CF/TP strands were measured statistically at various constant temperatures under wet and dry conditions. The statistical long-term creep and fatigue tensile strengths for CF/TP strands under wet and dry conditions are predicted by substituting the measured data into the formulations of these strengths on our developed ATM. Finally, the influences of water absorption on the statistical long-term creep and fatigue strengths of CF/TP strands are cleared. In particular, the degradation of relaxation modulus of matrix TP-EP resin with increasing of elapsed time is accelerated with the water absorption, and the degradation of creep strength of CF/TP strand with increasing of elapsed time is also accelerated with the water absorption in the similar manner of matrix resin. On the other hand, the fatigue strength of CF/TP strand decreases scarcely with water absorption although this fatigue strength depends remarkably on the number of cycles to failure.

The tensile strength along the longitudinal direction of unidirectional carbon fiber reinforced plastics (CFRPs) constitutes important data for the reliable design of CFRP structures. Our earlier reports proposed the formulations for the statistical static, creep, and fatigue strengths of CFRP based on Christensen’s model of the viscoelastic crack kinetics. This study is concerned with the statistical assessment of the tensile static, creep, and fatigue strengths of unidirectional CFRPs by using the proposed formulations and the characterization of the long-term strengths of unidirectional CFRPs. First, the proposed formulations for the time-dependent and temperature-dependent statistical static, creep, and fatigue strengths of CFRP are introduced. Second, the tensile static, creep and fatigue strengths of unidirectional CFRP are measured statistically at various temperatures using resin-impregnated CFRP strands as tensile test specimens by measuring the viscoelasticity of the matrix resin. Finally, the master curves showing the long-term life of these strengths are constructed by substituting these measured data into the formulations. The results clarify that the formulations are applicable with high reliability over wide ranges of time and temperature for the statistical tensile static, creep and fatigue strengths of unidirectional CFRP except above the glass transition temperature of the matrix resin. Therefore, the fatigue strength degradation phenomena of unidirectional CFRPs can be expressed by the time- and temperature-dependent part due to the viscoelastic behavior of the matrix resin and the number of load cycle-dependent parts. The long-term life prediction of unidirectional CFRPs under static, creep and fatigue tension loadings can be determined by ascertaining the mechanical properties of the CFRP and matrix resin in the proposed formulations.

Recently, the Innovative Composite Center of Kanazawa Institute of Technology developed a thermoplastic epoxy resin (TP-EP). Resin-impregnated carbon fiber reinforced TP-EP (CF/TP) strands molded by pultrusion were developed by Komatsu Matere Co., Ltd., for use as tension rods. This study examines the prediction of the statistical life time for these developed CF/TP strands under cyclic tension loading with comparison to our earlier report of similar predictions for carbon fiber reinforced thermoset epoxy resin (CF/TS) strands having a thermoset epoxy resin (TS-EP) as a matrix. First, test methods for static and fatigue strengths at elevated temperatures were developed for CF/TP strands. Second, static and fatigue tensile strengths of CF/TP strands were measured statistically at various constant temperatures under a constant strain rate and frequency. The master curves of statistical fatigue tensile strengths for CF/TP strands were constructed by substituting the measured data into the formulations of these strengths based on the matrix resin viscoelasticity. The fatigue strength characteristics of CF/TP strands were discussed through comparison to those of CF/TS strands with thermosetting epoxy resin as the matrix.

This paper describes the age-related warp of carbon fiber reinforced plastic (CFRP) asymmetric laminated beams due to the viscoelasticity, anisotropy, and nonhomogeneity of CFRP laminates. Asymmetric orthogonally laminated CFRP beams held at a high curing temperature were cooled at various rates with and without constraints against warping during cooling. Furthermore, the warping of CFRP beams with the constraint lifted after cooling was measured during the aging processes. The age-related warping generated under various conditions was predicted using the viscoelastic and thermal properties of the CFRP laminates. The results were compared with measured data. The results were interpreted as follows. The age-related warping of CFRP beams depends strongly on the process conditions of the cooling rate and constraint, and the thermal and physical age-related shrinkage and viscoelasticity in the transverse direction of unidirectional CFRP affect the age-related warp of CFRP beams. Thermoviscoelastic analysis with physical age-related shrinkage is effective for this prediction.

Recently, a carbon fiber/polypropylene unidirectional sheet has been developed by Mitsui Chemicals, Inc. from a new polyolefin-based sizing agent for carbon fiber. Its effective polypropylene modification brings good compatibility with polypropylene to improve the fiber matrix adhesion. This study examines the prediction of the statistical lifetime of this developed carbon fiber/polypropylene unidirectional sheet under creep tension loading. First, a tensile test method for static and creep strengths at elevated temperatures was developed for carbon fiber/polypropylene unidirectional tape cut from a carbon fiber/polypropylene unidirectional sheet. Second, the static tensile strengths of carbon fiber/polypropylene tape were measured statistically at various constant temperatures under a constant strain rate. The statistical creep failure times under tension loading for carbon fiber/polypropylene tape were predicted at a constant temperature by substituting the statistical static strengths into the formulation based on the matrix resin viscoelasticity. Third, the validity of the predicted results was clarified by comparison with the creep failure times measured statistically using creep tests for carbon fiber/polypropylene tape. Finally, the relation between the failure probability and creep failure times for carbon fiber/polypropylene unidirectional tape at various loads and temperature conditions was discussed.

The accelerated testing methodology (ATM) for the statistical life prediction of carbon fiber reinforced plastics (CFRP) under creep and fatigue loads based on the viscoelasticity of matrix resin has been proposed by authors. This method has been successfully applied to the life predictions of unidirectional CFRP with thermosetting epoxy resin as the matrix under tensile and flexural loads. In this paper, this method was applied to the fatigue life prediction of unidirectional CFRP (CF/PP laminates) with thermoplastic polypropylene (PP) as the matrix under tensile and flexural loads, and the effect of matrix viscoelasticity and load cycles on the fatigue behavior of CF/PP laminates were discussed under tensile and flexural loads. First, the viscoelasticity of matrix PP was measured. Second, the static and fatigue strengths of CF/PP laminates were statistically measured at various temperatures and frequencies under tensile and flexural loads. Third, all of material parameters in the fatigue strength formulation in ATM were determined using measured data, and the statistical long-term fatigue strengths of CF/PP laminates were predicted under tensile and flexural loads. As results, comparison with tension and bending test results clarified that the long-term tensile fatigue strength of CF/PP laminates decreases at an accelerated rate as the number of cycles increases, and that the flexural fatigue strength is affected by temperature and frequency rather than by the number of cycles to failure.

The formulation for time- and temperature-dependent statistical static and fatigue strengths for carbon fiber reinforced plastics laminates is newly proposed based on the physically serious role of resin viscoelasticity as the matrix of carbon fiber reinforced plastics. In this study, this formulation is applied to the tensile strength along the longitudinal direction of unidirectional carbon fiber reinforced plastics constituting the most important data for the reliable design of carbon fiber reinforced plastics structures which are exposed to elevated temperatures for a significant period of their operative life. The statistical distribution of the static and fatigue strengths under tension loading along the longitudinal direction of unidirectional carbon fiber reinforced plastics were measured at various temperatures by using resin-impregnated carbon fiber reinforced plastics strands as specimens. The master curves for the fatigue strength as well as the static strength of carbon fiber reinforced plastics strand were constructed based on the time–temperature superposition principle for the matrix resin viscoelasticity. The long-term fatigue strength of carbon fiber reinforced plastics strand can be predicted by using the master curve of fatigue strength.

For the past six years, we have been benefiting from the discovery by Tsai and Melo (2014) that the trace of the plane stress stiffness matrix ( tr ( Q ) ) of an orthotropic composite is a fundamental and powerful scaling property of laminated composite materials. Algebraically, tr ( Q ) turns out to be a measure of the summation of the moduli of the material. It is, therefore, a material property. Additionally, since tr ( Q ) is an invariant of the stiffness tensor Q , independently of the coordinate system, the number of layers, layup sequence and loading condition (in-plane or flexural) in a laminate, if the material system remains the same, tr ( Q ) = tr ( A ∗ ) = tr ( D ∗ ) is still the same. Therefore, tr ( Q ) is the total stiffness that one can work with making it one of the most powerful and fundamental concepts discovered in the theory of composites recently. By reducing the number of variables, this concept shall simplify the design, analysis and optimization of composite laminates, thus enabling lighter, stronger and better parts. The reduced number of variables shall result in reducing the number and type of tests required for characterization of composite laminates, thus reducing bureaucratic certification burden. These effects shall enable a new era in the progress of composites in the future. For the above-mentioned reasons, it is proposed here to call this fundamental property, tr ( Q ) , as Tsai’s Modulus.

A method for statistical prediction of the long-term creep failure time of CFRP using the statistical static strengths of CFRP at various temperatures and the viscoelasticity of matrix resin is proposed based on Christensen’s model of viscoelastic crack kinetics. The tensile strength along the longitudinal direction of unidirectional CFRP constitutes important data for the reliable design of CFRP structures. The authors developed a reliable method for testing creep and fatigue strengths as well as static strength at elevated temperatures for resin-impregnated carbon fiber strands (CFRP strands) as unidirectional CFRP. Two kinds of CFRP strands with two types of PAN-based carbon fibers with high strength and high modulus were examined on the viewpoint of failure mechanism. The statistical static strengths of these CFRP strands and the creep compliances of matrix resins were measured at various temperatures. The tensile creep failure times of these CFRP strands are predicted statistically based on a prediction method using measured data. The predicted creep failure times of these CFRP strands were compared with the creep failure times of these CFRP strands measured experimentally and statistically. Additionally, the statistical temperature-dependent static strengths are also discussed for CFRP strands of two types of pitch-based carbon fibers with low modulus and high modulus.

Long-term life prediction of carbon fiber reinforced polymers (CFRP) structures under cyclic loading is performed by multiscale modeling as the combination of fiber scale, layer scale, and structure scale. The concept of failure index for fiber and matrix based on the micromechanics of failure theory (MMF) developed by Sung-Kyu Ha is introduced for the determination of the failure corner in structure, failure layer in laminates, and failure mode of fiber or matrix. The accelerated testing methodology (ATM) developed by the authors is used for long-term life prediction of CFRP structures. An MMF/ATM method combined with MMF and ATM is applied to the long-term life prediction of open hole compressive CFRP laminates under cyclic loading as well as static loading. Then the predicted results are compared with the experimental ones. Results clarified that MMF/ATM method is useful for the long-term life prediction of CFRP structures under static and cyclic loading because the results mutually agree well.

An accelerated testing methodology (ATM) for measuring CFRP laminate durability developed by the authors over many years is reviewed in this paper. First, the applicability of ATM to static, creep, and fatigue strengths of various load directions for CFRP laminates of various kinds is examined experimentally based on time–temperature superposition principles for matrix resin viscoelasticity. Second, the formulation for time-dependent and temperature-dependent statistical static, creep, and fatigue strengths for CFRP laminates was done based on the matrix resin viscoelasticity. Third, these strengths of unidirectional CFRP were predicted statistically using the formulated equations. The predicted ones were compared with experimentally obtained data measured from resin-impregnated CFRP strands as specimens of unidirectional CFRP. Finally, the statistical long-term tensile static, creep, and fatigue strengths are discussed in terms of the role of the matrix resin viscoelasticity.

The statistical static strengths under the tension loading along the longitudinal direction of unidirectional CFRP with various kinds of carbon fibers are measured at various temperatures and discussed in the role of the viscoelasticity of matrix resin. First, the formulation for time and temperature dependent statistical static strength for CFRP laminates is performed based on the viscoelasticity of matrix resin. Second, the statistical static strengths of four kinds of carbon fibers, those are high strength and high modulus PAN based carbon fibers and low and high modulus pitch based carbon fibers, are measured by using single fibers of these four kinds of carbon fibers. Third, the temperature dependent tensile static strengths of unidirectional CFRP with four kinds of carbon fibers are statistically measured at various temperatures by using resin impregnated carbon fiber strands (CFRP strands) as the specimens of unidirectional CFRP, and the fractographs of CFRP strands with four kinds of carbon fibers failed at various temperatures are observed. Finally, the temperature dependences of tensile static strengths are discussed from the role of the viscoelasticity of matrix resin based on Christensen’s model of viscoelastic crack kinetics.

This study prepared textile carbon fiber reinforced polycarbonate laminates of three kinds molded with different conditions and carbon fiber reinforced epoxy laminates consisting of the same carbon fiber textile. Drop-weight impact tests were conducted for these four laminates with three levels of impact energies. The residual flexural strengths were measured after impact. Results show that the residual flexural strengths for all laminates decrease clearly with increasing impact energy. The flexural strengths of these laminates without impact damage have mutually different values. Furthermore, the laminates exhibit a decreasing ratio of residual flexural strength by impact damage with mutually differing values. The reasons were examined through observations conducted using ultrasonic flaw detection and digital microscope.

The size scaling of strength is examined for isotropic materials and for aligned fiber composite materials. The theoretical work follows the Weibull chain of links probabilistic form for the one dimensional cases. The three dimensional, brittle isotropic material theoretical result combines the Weibull chain of links form with a fracture mechanics requirement. The verification procedure involves single T300 carbon fiber testing at different fiber lengths. The aligned fiber strand testing is for standard T300/epoxy composites at different lengths. The theoretical predictions for the size dependence of tensile strength are in reasonable agreement with the testing results.

We have proposed the life prediction method for the statistical creep failure time under the tension loading along the longitudinal direction of unidirectional CFRP from the statistical static strengths of unidirectional CFRP measured at various temperatures. First, a method of predicting the statistical creep failure time of CFRP is explained briefly based on Christensen’s model of viscoelastic crack kinetics. Second, two types of unidirectional CFRP which consist of carbon fiber T300–3000 with thermosetting resin and thermoplastics as matrices, respectively. Third, the static strengths of these unidirectional CFRPs are experimentally and statistically measured at various temperatures. Then the creep failure times of these unidirectional CFRPs are predicted statistically using the statistical static strengths at various temperatures. Finally, the creep failure times of these unidirectional CFRPs are measured experimentally using these unidirectional CFRPs for comparison with the predicted ones.

The method of predicting the statistical creep failure time under the tension loading along the longitudinal direction of unidirectional CFRP from the statistical static strengths of this CFRP measured at various temperatures is applied to various unidirectional CFRP with different kinds of carbon fibers. Two kinds of CFRP strands with two kinds of PAN based carbon fibers as specimens for unidirectional CFRP are prepared. The static strengths of these CFRP strands are experimentally and statistically measured at various temperatures. Then the creep failure times of these CFRP strands are predicted statistically using the statistical static strengths based on the predicting method. Finally, the creep failure times of these CFRP strands at a constant load and a temperature are measured experimentally and probabilistically using these CFRP strands for comparison with the predicted ones. Additionally, the predicting method is also applied to two kinds of CFRP strands with two kinds of pitch based carbon fibers.

This study examines the effect of stamping condition on age deformation after stamping of textile carbon fiber reinforced polycarbonate laminates. The laminates were stamped to a hat shape at various stamping temperatures between the glass transition temperature Tg and the melting temperature Tm of polycarbonate. Then the age deformation, which is the hat angle variation, was measured. Results show that the age deformation occurs at the stamping temperature in the vicinity of Tg. The age deformation is suppressed when the stamping temperature is sufficiently higher than Tg. Furthermore, the long-term age deformation as the dimensional stability was predicted from the measured deformation at elevated temperature based on the time–temperature superposition principle for the viscoelasticity of the polycarbonate matrix.

The effects of molding conditions on the flexural strength of textile carbon fiber reinforced polycarbonate laminates were assessed. Choosing the temperature and pressure conditions appropriately during hot-press molding using carbon fiber textile layers and polycarbonate films can produce void-free, high interfacial adhesion in textile carbon fiber reinforced polycarbonate laminates. Those characteristics were confirmed from observing the cross-sections of carbon fiber reinforced polycarbonate laminates and measuring the interlaminar shear strength. A suitable molding condition can raise the flexural strength of carbon fiber reinforced polycarbonate laminates to a level predicted from the measured flexural strength of textile carbon fiber/epoxy laminates by assuming carbon fiber micro-buckling in the compression side of specimens.

The tensile strength along the longitudinal direction of unidirectional CFRP is one of the important data for the reliable design of CFRP structures. This paper is concerned with the statistical prediction of creep failure time under the tension loading along the longitudinal direction of unidirectional CFRP based on the viscoelasticity of matrix resin. It was cleared in this study that the statistical creep failure time under the tension loading along the longitudinal direction of unidirectional CFRP can be predicted by using the statistical static tensile strengths of carbon mono filament and unidirectional CFRP and the viscoelasticity of matrix resin based on Christensen’s model of viscoelastic crack kinetics.

An advanced accelerated testing methodology (ATM-2) for long-term life prediction of CFRP laminates exposed to actual loading with a general stress and temperature history is proposed based on the conventional accelerated testing methodology (ATM-1) established for the long-term life prediction of CFRP laminates exposed to stress and temperature. The most important condition for ATM-1 is that the time–temperature superposition principle held for the viscoelastic behavior of matrix resin holds also for the static, creep, and fatigue strengths of CFRP laminates. Furthermore, three conditions that form the basis of ATM-2 are introduced along with their scientific bases. The long-term fatigue strength of CFRP laminates under an actual loading is formulated based on the three conditions. The viscoelastic coefficients of matrix resin, which perform an important role for the time and temperature dependence of long-term life of CFRP laminates, are also formulated based on the time–temperature superposition principle. The applicability of ATM-2 is demonstrated by predicting the long-term fatigue strengths of four typical directions of unidirectional CFRP laminates.

This paper is concerned with the characteristics of the temperature-dependent tensile strength along the longitudinal direction of the unidirectional carbon fiber-reinforced plastic. The temperature-dependent tensile strength of the unidirectional carbon fiber-reinforced plastic was evaluated using resin-impregnated carbon fiber strand (carbon fiber-reinforced plastic strand) specimens with highly reliable co-cured tabs developed by the authors. The tensile strength of carbon fiber-reinforced plastic strand was measured at three constant temperatures below the glass transition temperature of the matrix resin for 50 specimens at each temperature. The results showed that the tensile strength of the unidirectional carbon fiber-reinforced plastic has a Weibull distribution at each temperature. The shape parameter of the tensile strength does not change with the temperatures and the scale parameter decreases clearly with increasing temperature. The degradation rate of the tensile strength of the unidirectional carbon fiber-reinforced plastic by the temperature raise against that of the viscoelastic modulus of the matrix resin agrees well with the predicted results based on the Rosen’s strength analysis.

This article is concerned with the reliable test method for measuring the tensile strength in the longitudinal direction of unidirectional carbon fiber-reinforced plastics. A filament-wound resin-impregnated carbon fiber strand (carbon fiber-reinforced plastics strand) was employed as the specimen. The most important improvement for reliable tests is that the bonding strength of the end tabs with carbon fiber-reinforced plastics strand should be higher than the tensile strength of CFRP strand. We improved the bonding strength by co-curing the carbon fiber-reinforced plastics strand with end tabs. The improved method was applied to two kinds of carbon fiber-reinforced plastics strands and the reliable tensile strengths were obtained.

The accelerated testing methodology (ATM) developed by the authors is introduced for predicting the long-term life of CFRP laminates by using the static, creep and fatigue strengths of them measured at a short term and various temperatures. First, the time-temperature superposition principle (TTSP) held for the viscoelasticity of matrix resin is explained by using the viscoelastic model. Second, the master curves of these strengths of CFRP laminates in the wide range of failure time at a reference temperature are constructed using TTSP for the viscoelasticity of matrix resin. Third, the master curves of CFRP strengths are statistically formulated based on Christensen’s viscoelastic crack kinetic theory. Finally, the applicability of life prediction by ATM is discussed for various CFRP laminates and structures.

This study was concerned with the effect of stamping condition on age deformation after stamping for textile carbon fiber reinforced Polycarbonate (CF/PC) laminates. The textile CF/PC laminates were stamped to hat shape under various stamping temperatures. The specimens were held at several exposure temperatures into the constant temperature chamber after stamping process and the variations of hat angle against exposure time were measured. As results, it is cleared that the age deformation is suppressed with increasing stamping temperature. The variation of hat angle as the long-term dimensional stability can be predicted from the measured data at elevated temperatures based on the time-temperature superposition principle which is held for the viscoelasticity of matrix polycarbonate.

The time- and temperature-\dependent static strengths for typical three directions of unidirectional carbon fiber reinforced plastic, which are the tensile and compressive static strengths for the longitudinal direction and the tensile static strength for the transverse direction, were measured at various deformation rates and temperatures in our previous paper. By using these measured data, the master curves of these static strengths are constructed based on the time–temperature superposition principle to be held for the viscoelastic behavior of matrix resin. Furthermore, the relationships between the viscoelastic behavior of matrix resin and these static strengths are evaluated on the viewpoints of failure mechanism. The quantitative characteristics of these static strength master curves are discussed using the formulation based on their failure mechanisms.

The time-temperature superposition principle has been applied to predict accurately the long-term viscoelastic behavior of amorphous resin at a temperature below the glass transition temperature from measuring the short-term viscoelastic behavior at elevated temperatures. A simplified method for the determination of the long-term viscoelastic behavior of amorphous resin using dynamic mechanical analysis is proposed. The automatic horizontal and vertical shifting method is used to construct the smooth storage modulus master curve, and then the accurate time-temperature shift factors can be obtained. The validity of our simplified determination method is confirmed experimentally.

Accepted: 2011-10-17, 資料番号: SA1003646000

This study examines the applicability of the SFF model (Koyanagi J, Kotani M, Hatta H and Kawada H. A comprehensive model for determining tensile strengths of various unidirectional composites. J Compos Mater 2009; 43: 1901–1914) to the time and temperature dependence of strength for two kinds of CFRP. The only difference in the materials is the reinforcing carbon fiber, which is not time or temperature-dependent; the time and temperature dependence of strength for the two materials differ. The SFF model, however, can follow their strengths well. Postulating the SFF applicability, the validity of the conventional accelerated testing methodology by elevated temperature and a simple method to predict long-term durability, including creep lifetime, are discussed.

This paper deals with the prediction of long-term viscoelastic behavior of amorphous resin at a temperature below the glass transition temperature T g from measuring the short-term viscoelastic behavior at elevated temperatures based on the time-temperature superposition principle (TTSP) with vertical shift as well as horizontal shift. The long-term creep compliance as well as short-term and medium-term creep compliances were measured at elevated temperatures. The master curves of creep compliance can be constructed from measured data by shifting vertically as well as horizontally. The master curves of creep compliance constructed from measured data by short-term and medium-term creep tests agree well with those measured by long-term creep tests. Furthermore, the horizontal and vertical shift factors obtained from constructing the master curve are independent of the time period of creep tests. Therefore, the long-term viscoelastic behavior at a temperature below T g can be predicted accurately from measuring the short-term viscoelastic behavior at elevated temperatures based on the TTSP with vertical shift as well as horizontal shift.

Our proposed accelerated testing methodology (ATM) for the long-term life prediction of polymer matrix composites and structures is based on the time-temperature superposition principle to be held for the viscoelasticity of polymer matrix. This article is concerned with the life prediction of CFRP/metal bolted joint under water absorption condition based on ATM. CFRP/metal bolted joints were prepared under three conditions of ‘Dry,’ ‘Wet,’ and ‘Wet + Dry.’ The tensile static and fatigue tests of CFRP/metal bolted joints under these three conditions were performed at various loading rates and temperatures. As a result, the master curves of static and fatigue failure loads of these joints for the long-term life prediction were obtained and the influence of water absorption on the long-term life of these joints was cleared.

The prediction of long-term fatigue life of various FRP laminates combined with resins, fibers and fabrics for marine use under temperature and water environments were performed by our developed accelerated testing methodology based on the time–temperature superposition principle (TTSP). The five kinds of FRP laminates were prepared under three water absorption conditions of Dry, Wet and Wet + Dry after molding. The three-point bending constant strain rate (CSR) and fatigue tests for these FRP laminates at three conditions of water absorption were carried out at various temperatures and loading rates. As results, the mater curves of fatigue strength as well as CSR strength for these FRP laminates at three water absorption conditions are constructed by using the test data based on TTSP. It is possible to predict the long-term fatigue life for these FRP laminates under an arbitrary temperature and water absorption conditions by using the master curves. The characteristics of time, temperature and water absorption dependencies of flexural CSR and fatigue strengths of these FRP laminates are clarified.

This article proposes a new concept of residual strength master curves for damaged carbon fiber-reinforced plastic (CFRP) after various spectral creep and fatigue loadings by using master curves for pristine CFRP, based on an accelerated testing methodology (ATM) and a statistical linear cumulative damage (SLCD) rule. Three-point bending fatigue tests for plain-woven CFRP composites were carried out under various cyclic loadings with both constant and variable amplitudes and frequencies. It was shown from the viewpoint of statistics that the SLCD rule can be applicable to the prediction of the flexural fatigue life of these CFRP composites under variable amplitudes and frequencies of cyclic loading. A method to construct the master curve of residual strengths for damaged CFRP from the master curves of creep and fatigue strengths for pristine materials was introduced.

This paper deals with the prediction of long-term strength of CFRP structure components based on the combined method of the strain invariant failure theory (SIFT) developed by Gosse and Christensen and the accelerated testing methodology (ATM) developed by Miyano and Nakada. The time—temperaturedependent master curves of SIFT critical parameters are constructed by tension and compression tests for the longitudinal and transverse directions of unidirectional CFRP under various temperatures based on the time-temperature superposition principle which holds for the viscoelastic modulus of matrix resin. These master curves can be used for predicting the long-term strength of composite structures with multi-directional laminations at any time, temperature. The long-term open-hole compression strength of the quasi-isotropic CFRP laminates is predicted using the master curves of SIFT critical parameters based on SIFT/ATM combined method and structural stress and strain analysis by finite element method. The applicability of SIFT/ATM combined method to predict the long-term strength of CFRP structures is experimentally confirmed.

A prediction method for the fatigue life of polymer composites under arbitrary frequency, load ratio and temperature was extended to that of polymer composite structures. The three-point bending tests for honeycomb cored sandwich (SW) panels with GFRP skin plates and Nomex honeycomb core under constant strain rates (CSR) and fatigue loading at various strain rates and temperatures were conducted. The maximum bending moments for CSR and fatigue loadings strongly depend on time and temperature, and the time—temperature superposition principle for the storage modulus of matrix resin holds for the maximum bending moments for fatigue loading as well as CSR loading. The long term fatigue strength at any time, temperature and number of cycles to failure can be predicted using the master curves of the bending moment by fatigue loading based on the accelerated testing methodology.