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| 2. |
- Andersons, J., et al.
(författare)
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Fibre fragment distribution in a single-fibre composite tension test
- 2001
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Ingår i: Composites Part B. - 1359-8368 .- 1879-1069. ; 32:4, s. 323-332
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Tidskriftsartikel (refereegranskat)abstract
- Single fibre fragmentation tests are performed for brittle fibres with Weibull strength distribution and different surface treatments. The fragmentation process is modelled and closed-form expressions for break spacing distribution are obtained. The model accounts for the effect of finite fibre length on the initial fragmentation as well as for break interaction on the advanced fragmentation stage. It is assumed that the exclusion zone due to fibre-matrix interface failure and stress recovery in the fibre is linearly dependent on the applied load. This assumption is validated experimentally. The derived theoretical average fragment length dependence on applied load is used to determine the fibre strength distribution parameters and the effective interfacial shear stress for carbon/epoxy single fibre composites with different fibre surface treatment and for glass/vinylester single fibre composite. Fragment length distribution is predicted for several load levels. Predictions are in good agreement with experimental data
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| 3. |
- Andersons, J., et al.
(författare)
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Glass fibre strength distribution determined by common experimental methods
- 2002
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 62:1, s. 131-145
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Tidskriftsartikel (refereegranskat)abstract
- The tensile strength of brittle fibres is routinely described by the Weibull distribution. The parameters of the distribution can be obtained from tests on single fibres and fibre bundles or from model composite tests. However, there is growing evidence that the distribution parameters obtained by different experimental techniques differ systematically. In order to investigate the possible causes of such discrepancies, single-fibre tension, fibre bundle, and single-fibre fragmentation tests are employed in this study to obtain strength distribution of commercial E-glass fibres. The results reveal parameter dependence on the approach used to extract the distribution parameters from experimental data. Particularly, in the case of single-fibre tension tests, the shape parameter obtained from average fibre strength vs. length data is larger than that obtained at a fixed gauge length. It is assumed that the apparent fibre strength scatter is caused by both the inherent flaw structure along a fibre and by the fibre-to-fibre strength variability within a batch, due to slightly differing processing and handling history of the fibres. Fibre fragmentation test results are used to derive the Weibull distribution parameters applicable to the fibre batch. The strength distribution obtained is compared with strength data for the single fibres, and reasonably good agreement is observed.
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| 4. |
- Bonde, J P, et al.
(författare)
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Sperm count and chromatin structure in men exposed to inorganic lead: lowest adverse effect levels
- 2002
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Ingår i: Occupational and Environmental Medicine. - 1470-7926. ; 59:4, s. 234-234
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To obtain knowledge on male reproductive toxicity of inorganic lead at current European exposure levels and to establish lowest adverse effect levels, if any. METHODS: A cross sectional survey of the semen of 503 men employed by 10 companies was conducted in the United Kingdom, Italy, and Belgium. The mean blood lead concentration was 31.0 microg/dl (range 4.6-64.5) in 362 workers exposed to lead and 4.4 microg/dl (range below the detection limit of 19.8) in 141 reference workers. Semen volume and sperm concentration were determined in a fresh semen sample according to an agreed protocol subject to quality assurance. The sperm chromatin structure assay (SCSA) was performed at a centralised laboratory. Extraneous determinants including centre, period of sexual abstinence, and age were taken into account in the statistical analysis. If appropriate, possible thresholds were examined by iterative threshold slope linear regression. RESULTS: The median sperm concentration was reduced by 49% in men with blood lead concentration above 50 microg/dl. There was no indication of a linear trend of lower sperm concentration with increasing blood lead values, but threshold slope least square regression identified a blood lead concentration of 44 microg/dl (beta=-0.037, F=4.35, p=0.038) as a likely threshold. Abnormal sperm chromatin structure was not related to blood lead concentration, but some indications of deterioration of sperm chromatin was found in men with the highest concentrations of lead within spermatozoa. Biological monitoring data did not indicate long term effects of lead on semen quantity or sperm chromatin. CONCLUSION: Adverse effects of lead on sperm concentration and susceptibility to acid induced denaturation of sperm chromatin are unlikely at blood lead concentrations below 45 microg/dl. Effects of low level exposure to lead on other measures of testicular function cannot be ruled out.
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| 5. |
- Kislev, T., et al.
(författare)
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On the nature of opaque cylindrical regions formed at fibre break sites in a fragmentation test
- 2002
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Ingår i: Advanced Composites Letters. - : SAGE Publications. - 0963-6935 .- 2633-366X. ; 11:1, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- When a single-fibre composite test is performed to obtain information about the interfacial adhesion in a composite, a gradual strain increase often causes an opaque (black) cylinder to nucleate at, and grow from, the fibre failure sites. The nature of the opaque cylinder is difficult to ascertain using optical microscopy. This is the subject of the present note. To study the inside of the opaque cylinder we use several experimental methods based on imaging the failed region: optical microscopy, laser Raman spectroscopy and scanning electron microscopy. Mechanical models, including FEM analysis and analytic equations based on the shear-lag, approach, are used to discuss the experimental work. The nature and growth mechanism of the opaque cylinder are of importance in defining the parameters and/or contributions that appear in both the force balance and the. energy balance schemes.
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