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Degradation and damage of advanced laminate polymer composites due to environmental effects and low velocity impact.
Dostępność: jest w magazynie sklepu
Dostępna ilość: 1
Autor
Specyfikacja książki
Ilość stron
130
Okładka
miękka
Format
B5
Rok wydania
2005 - wyd. I
Język
angielski

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This work focuses on environmental and low velocity impact behaviour (also studied in combination) of advanced laminates which have been proposed for high performance marine applications. The author's experimental results are summarized and the data are interpreted in the context of relevant available literature data and postulated theoretical analyses. The materials studied comprised woven fabric reinforcement and cold setting resin systems (epoxy or vinyl ester) and were manufactured by pressure bagging or hand lay-up. The fibre systems were simple carbon, glass, aramid and advanced hybrid: aramid-glass aramid carbon and carbon-glass. For these materials there is scant knowledge regarding their behaviour in marine environments, under impact and for combination of these demanding service conditions. Impact damage tolerance has also been analysed, with respect to the phenomena observed in the matrix, fibres or at the interfaces of the composite. Again, such studies are quite rare in the case of marine laminates.
In contrast to aerospace composites (where short- term repeated absorption and desorption processes mainly affect the composite matrix), it has been shown that in shipbuilding laminates, permanently or periodically immersed in water, matrix plasticisation controls only the first stage of the lengthy process of laminate degradation. Accordingly matrix and fibre properties and the interfacial bond strength, rather than water absorption characteristics of neat matrix resin, need to be considered. Thus, using the concept of "attributed water uptake in the matrix", the author separated matrix effects from interface and fibre effects in GFRP at 323K. This permitted:(i) the identification of the exposure period when water diffusion is mainly in the matrix: 20 - 25 days and (ii) the proportion of water uptake attributed to the interfaces and fibres (transport along the interfaces): 45 - 55% in one year exposure. Water absorption curves for simple and hybrid fibre reinforced composites showed socalled normal behaviour, with saturation in water uptake observed within 8 months exposure period. Consequently, to estimate diffusivities in the individual laminates, Fickian diffusion was used as a reasonable approximation. The rule of mixtures gave a good prediction of both diffusivities and saturation water uptake in intermixed hybrid aramid-glass fibre laminates. For interlayer aramid-carbon fibre composites, however, higher values of diffusivities and saturation water uptake were observed than the values predicted, because of the strong effect of the permeable aramid fibre external ply.
In order to account for the hybrid reinforcement and water immersion effects on flexural behaviour of the water immersed laminates, the author plotted failure maps. These show, as a function of water content, the failure stresses (strains) corresponding to the described failure mechanisms. The water immersion tests under constant load showed that brittle cracking observed in GFRP is significantly retarded in woven (A - G)FRP, due to the complex failure mechanism then operating. In contrast, exposure to dilute nitric and sulphuric acids affected both GFRP and (A - G)FRP, which resulted in significantly reduced work of fracture determined in tension.
Impact damage was detected and characterized using the new ultrasonic air-coupled C-scan and X-ray radiographic techniques. The air coupled ultrasonic technique was found very effective and compares well with the results of impact damage in CFRL obtained using the X-ray technique. The C-scan tests showed that in aramid-carbon plates internal damage corresponds to the external damage; consequently visual inspection of such plates can be quite reliable. For CFRP plates, however, the internal damage is always much more extensive, which justifies the need of non-destructive tests. Investigations were of: (1) the effect of epoxy matrix reinforcement by solid /hollow particles, (2) the impact threshold damage and impact damage tolerance in interlayer (G - C)FR laminates, (3) the effect of water immersion ageing on impact damage size and (4) the compression strength after impact. The use of epoxy matrix filler (20% solid glass beads) resulted in significant reductions (20 - 100%) of projected impact damage area and high retention of post impact tensile strength (up to 85%) compared to 45% for unmodified composite. Comparison of GFRL with vinyl ester and epoxy matrices in terms of impact tolerance showed superiour behaviour of vinyl ester matrix with higher maximum impact force (impact resistance) and compression strength after impact (impact damage tolerance).
In the absence of instrumented impact tester (found only in specialist laboratories), static incremental tests, accompanied by acoustic emission recording of the on-going damage process, were found useful in the determination of threshold damage energy. The results of such static and dynamic tests are found in good agreement for carbon and (G - C)FRP. In terms of impact damage tolerance, GFRP showed lower (15%) flexural strength reduction compared to (G - C)FRP (30%).
Impact damage area in aramid-glass interlayer and intermixed /epoxy laminates was slightly less extensive in wet samples This implies propagation of interfacial damage present in wet samples prior to impact, which absorbed impact energy and inhibited transverse ply fracture. The compression strength of the two composites suffered 28% reduction due to water absorption (undamaged condition) and maximum of 42% with the impact of incident energy 32 J (wet samples). Wet samples of interlayer composite were less sensitive to impact than wet intermixed samples, which resulted in higher (minimum) compression strength retention factors of 0.77 and 0.63, respectively. The predicted values of threshold impact energy for (A - G)FR and GFR plates were: 10 and 8 J, respectively, which is in good agreement with the instrumented impact test results. It was shown that the knowledge of threshold damage impact energy is especially important in the context of assessment of specific impact events, which can cause damage in the real laminate structure. Predictions of threshold damage impact energy and compression strength after impact in interlayer and intermixed (A - G)FR/epoxy composites in dry and wet conditions were made and compare favourably with experimental data.

Spis treści:

CONTENTS
LIST OF SYMBOLS AND ABBREVIATIONS
AIM AND OBJECTIVES OF THE RESEARCH

1. INTRODUCTION

2. ENVIRONMENTAL DEGRADATION OF GLASS, CARBON, ARAMID AND HYBRID FIBRE EINFORCED/EPOXY LAMINATES
2.1. Introduction. Environmental degradation of fibre-reinforced polymer composites
2.1.1. Mechanisms of failure due to water absorption
2.1.2. Environmental effects in constituent materials
2.2. Water absorption and its effect on the mechanical performance in carbon, glass, aramid and hybrid-fibre reinforced epoxy laminates
2.2.1. Water absorption kinetics
2.2.2. Effect of voids (fabrication)
2.2.3. Matrix effects
2.2.4. Interfacial effects
2.2.5. Simple and hybrid fibre effects on water absorption kinetics in glass, carbon, and aramid fibre reinforced epoxy laminates
2.2.6. Mechanical degradation and failure mechanisms in simple and hybrid fibre composites
2.2.7. Failure maps in the epoxy composites reinforced with glass, carbon, aramid and hybrid fibres
2.3. Environmental stress cracking in E-glass and aramid-glass/epoxy composites
2.3.1. Environmental crack propagation under constant loading in glass and aramid-glass/epoxy composites
2.3.2. Effect of acid environment on tensile behaviour of aramid-glass fibre reinforced laminates

3. LOW VELOCITY IMPACT TOLERANCE AND FAILURE MECHANISMS IN ADVANCED POLYMER LAMINATES
3.1. Impact tolerance through the use of novel materials and processing
3.2. Impact damage detection
3.2.1. Experimental techniques for impact damage assessment
3.2.2. Impact damage detection in carbon and hybrid fibre/epoxy laminates
3.2.3. Impact damage response of hybrid laminates
3.3. Impact tolerance in glass and hybrid fibre reinforced polymer laminates: matrix and fibre effects
3.3.1. Effect of matrix fillers on impact behaviour of glass/epoxy laminates
3.3.2. Effect of matrix resin type on impact damage tolerance in glass fibre-reinforced laminates
3.3.3. Influence of carbon fibre interlayers on the response of woven glass/carbon/epoxy panels to low velocity impact

4. THE EFFECT OF WATER IMMERSION AGEING ON LOW VELOCITY IMPACT BEHAVIOUR OF WOVEN ARAMID-GLASS FIBRE/EPOXY LAMINATES

5. MODELLING OF THE IMPACT BEHAVIOUR IN POLYMER LAMINATES
5.1. Modelling of the impact damage threshold energy in glass and aramid-glass/ epoxy composites
5.2. Modelling of the laminate strength after impact

6. CONCLUSIONS
6.1. Environmental degradation of glass, carbon, aramid and hybrid-fibre reinforced/epoxy laminates
6.2. Low velocity impact tolerance and failure mechanisms in advanced polymer laminates

7. DISCUSSION OF THE AUTHOR'S RESULTS IN THE CONTEXT OF THE STATE-OF-THE ART REFERENCES

SUMMARY IN ENGLISH
SUMMARY IN POLISH

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