| 1. |
- Berglund, Lars A., et al.
(författare)
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Effect of intralaminar toughness on the transverse cracking strain in cross-ply laminates
- 1991
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Ingår i: Advanced Composite Materials. - 0924-3046 .- 1568-5519. ; 1:3, s. 225-234
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Tidskriftsartikel (refereegranskat)abstract
- The effect of toughness on the onset of transverse cracking was studied in [0m/90n]s cross-ply laminates. Experimental observations indicated that carbon fiber composites based on tougher matrices show weaker constraint effect although their mechanical cracking strain improves in the low constraint region. From LEFM theory it was predicted that the total transverse cracking strain in a thick 90-deg layer of a cross-ply laminate is 1 . 58 times higher than the transverse failure strain of the unidirectional composite. This was verified by experimental data. The LEFM-based model by Isida was applied to the transverse cracking problem in order to predict the total transverse cracking strain for different cross-ply laminates. Model predictions showed good agreement with experimental data for the brittle matrix T300/934 carbon fiber composite. However, for carbon fiber composites the predictions did not describe the experimentally observed weakening of the constraint effect with increasing toughness.
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| 2. |
- Berglund, Lars A., et al.
(författare)
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Transverse Cracking and Local Delamination in [04/90n]s and [90n/04]s Carbon Fiber/Toughened Epoxy Laminates
- 1992
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Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 11:6, s. 643-660
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Tidskriftsartikel (refereegranskat)abstract
- [04/90n]s and [90n/04 ]s laminates were used to study 90°-layer failure mechanisms in HTA/6376 carbon fiber/toughened epoxy. The different stacking sequences were chosen to vary the stress states, since experimental results show differences in failure strains as well as in the local delamination behavior at the crack tip. Differences in the onset of transverse cracking and local delamination behavior between [04/90m]s and [90 n/04]s laminates was discussed using a model based on linear elastic fracture mechanics (LEFM). Although quantitative LEFM-predictions do not agree with data for the carbon fiber/toughened epoxy investigated, the general predictions for differences in and causes of local delamination behavior were confirmed by experimental data. The fact that the main features were correctly predicted, encourages the development of some modified LEFM-approach to describe toughened matrix composites.
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| 3. |
- Berglund, Lars A., et al.
(författare)
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Transverse cracking in laminated composites
- 1995
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Ingår i: Advanced technology for design and fabrication of composite materials and structures. - : Kluwer Academic Publishers. - 0792333039 ; , s. 191-201
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Konferensbidrag (refereegranskat)abstract
- Models based on variational analysis are compared with respect to the elastic properties of cross-ply laminates with transverse cracks. All models use the principle of minimum complementary energy for calculation of the stress state in a laminate element between two cracks, as was the case with the original model by Hashin (1985). The models are based on assumptions of different degree of accuracy, where the most refined model was developed by the present authors. Experimental data for the longitudinal stiffness are compared with predictions for glass fiber/epoxy cross-ply laminates. The agreement between model predictions and data is good provided the initial assumptions of the stress state are sufficiently accurate
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| 4. |
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| 5. |
- Jacobs, Edgard, et al.
(författare)
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On the use and limitations of concentric cylinder models for polymer matrix composites
- 1999
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Ingår i: ICCM-12 Europe. - Tours : ICCM. - 2951452624
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Konferensbidrag (refereegranskat)abstract
- Models to calculate the stiffness matrix of a unidirectional composite involve often the use of a concentric cylinder as unit cell. In this paper, an existing concentric cylinder model of Pagano&Tandon has been extended, by applying the Mori-Tanaka and generalised self-consistent scheme theories to this basic model. The aim is to improve the stiffness prediction for three phase composite systems. It will also be pointed out that, although improvements in stiffness prediction can be achieved, the use of these concentric cylinder models for local stress state analysis in polymer matrix composites is rather questionable.
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| 6. |
- Joffe, Roberts, et al.
(författare)
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Acoustic emission from composite laminates with simple damage characteristics
- 1995
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Ingår i: Fifth International Symposium on Acoustic Emission from Composite Materials, July 10-14, 1995, Sundsvall's KonferensCenter, Hotel Sundsvall, Sundsvall Sweden. - Columbus, Ohio : American Society for Nondestructive Testing. - 157117012X ; , s. 179-186
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Konferensbidrag (refereegranskat)abstract
- Interpretation of acoustic emission (AE) signals in terms of damage mechanisms in composite materials and structures is often difficult. This is because of the multitude of damage mechanisms. In the present study, glass fiber/epoxy (GF/EP) (0m/90n)s cross-ply laminates were studied in unixial tensile loading. Since the damage mechanisms in such laminates are primarily matrix cracking, acoustic emission interpretation was facilitated. Real-time optical microscopy and AE studies were conducted in order to identify details of the damage development. It was found that a multitude of secondary cracking events occurred at higher strains. These events may explain why stress analysis models based on straight and regularly spaced transverse cracks are not successful. In addition, it was clearly demonstrated that in order to interpret damage development with some confidence from AE-data, direct observations of damage events must also be performed.
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| 7. |
- Joffe, Roberts, et al.
(författare)
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Analysis of single fiber fragmentation data
- 1995
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Ingår i: Deformation and fracture of composites : 3rd International conference. - London : Institute of metals. ; , s. 126-131
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Konferensbidrag (refereegranskat)
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| 8. |
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| 9. |
- Joffe, Roberts, et al.
(författare)
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Analytical modeling of stiffness reduction in symmetric and balanced laminates due to cracks in 90° layers
- 1999
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 59:11, s. 1641-1652
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Tidskriftsartikel (refereegranskat)abstract
- Stiffness reduction in [S,90n]s symmetric laminates, containing orthotropic sub-laminates (S) and cracked 90° layer, is analyzed. Closed-form expressions relating stiffness changes to the transverse crack density are derived. They contain only material properties, laminate geometry and a stress-perturbation function that is proportional to the normalized average crack-opening displacement. Stress-distribution models [shear lag, based on variational approach, and finite-element analysis (FEA)] are adopted for the [S,90n]s configurations and used to calculate the stress-perturbation function. Predictions are compared with experimental data for [θ, 904]s θ=0, 15, 30, 40 glass-fiber/epoxy-resin laminates. Generally the FEA model slightly underestimates stiffness reduction whereas both of the variational models used lead to similar results, slightly lower than experimental. Even the shear-lag model may be successfully used if the shear-lag parameter is first obtained from fitting test results for cross-ply laminate of the same material.
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| 10. |
- Joffe, Roberts, et al.
(författare)
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Damage evolution modeling in multidiractional laminates and the resulting nonlinear response
- 1999
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Ingår i: ICCM-12 Europe. - Tours : ICCM. - 2951452624
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Konferensbidrag (refereegranskat)abstract
- Stiffness reduction in [S,90n]s symmetric laminates, containing orthotropic sub-laminates (S) is analyzed as a function of crack density in 900 layer. Closed form expressions relating stiffness changes to the transverse crack density are used to compute stiffness changes due to accumulated damage. Weibull strength distribution of 900 layer is assumed and Shear Lag and Hashin’s models are used for calculation of stress distribution in 900 layer with cracks. Weibull parameters are obtained from experimental data for [02, 904]s laminate and then used for other lay-ups. Strength approach and Monte-Carlo simulation is used to estimate damage evolution in 900 layer and crack density as a function of applied strain is obtained. It is used to predict stiffness changes in [S,90n]s laminates as a function of applied strain. Predictions are compared with experimental data for [±θ, 904]s θ= 0,15,30,40 GF/EP laminates. Comparison shows fairly good agreement between prediction and experimental.
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