| 1. |
- Asp, Leif, et al.
(författare)
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Prediction of failure initiation in polypropylene with glass beads
- 1997
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 9-15
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Tidskriftsartikel (refereegranskat)abstract
- The effect of glass bead content and residual stresses on failure initiation in isotactic polypropylene composites has been investigated by finite element analysis for the cases of interfacial debonding, plastic yielding, and cavitation. Residual thermal stresses are demonstrated to have a large effect on global failure initiation stress. Yielding and cavitation occur at higher global stresses than debonding. Modeling results, as well as previous experimental data, support debonding as the initial failure mechanism
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| 2. |
- Gebart, Rikard, et al.
(författare)
-
Measurement of in-plane permeability of anisotropic fiber reinforcements
- 1996
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 17:1, s. 43-51
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Tidskriftsartikel (refereegranskat)abstract
- Three of the most common methods (two with parallel flow and one with radial flow) for determination of the in-plane permeability tensor are studied both theoretically and experimentally. An error analysis shows that the difference between the methods is negligible if the error levels are equal. However, the radial flow method is found to be susceptible to large errors from mold deflection in an experimental comparison between the methods. Additional experiments with the radial flow method in a stiffer mold show that the method gives the same values for the permeability tensor as the other two methods. A new method with multiple cavities in parallel is proposed that combines the simplicity of the radial flow method with the stiff mold of the parallel flow method. Only mass and time need to be measured in one experiment and it eliminates the need to measure fluid viscosity, temperature, and injection pressure. The method depends on the availability of a reference material with known permeability.
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| 3. |
- Lindhagen, Johan, et al.
(författare)
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Notch sensitivity and damage mechanisms of glass mat reinforced polypropylene
- 1997
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 40-47
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Tidskriftsartikel (refereegranskat)abstract
- Notch Sensitivities of two structurally different glass-mat reinforced polypropylene materials (GMT) were investigated. Center hole notches in tensile specimens were used in the tests. The results show that the short fiber material has higher unnotched strength, but also higher notch sensitivity compared to a swirled mat material. Reasons for this are discussed, focusing on microstructural differences. Predictions from four different failure criteria were compared with the experimental notched strength data. The point stress and damage zone criteria were found to give the best descriptions.
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| 4. |
- Lundström, Staffan
(författare)
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Bubble transport through constricted capillary tubes with application to resin transfer molding
- 1996
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 17:6, s. 770-779
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes and expounds a theoretical and experimental study of bubble motion through constricted capillary tubes. In the experiment, two liquidfilled capillaries are used. They have unequal radii and are glued together. Gas bubbles are injected into the larger capillary. Then the pressure required to force the bubbles through the constriction is measured for various liquids, bubble lengths, capillary radii and constriction geometry. It appears that the pressure directly follows Young's-Laplace law for capillary pressure. The results of the study are used to understand the bubble transport through fiber reinforcements, which generally takes place during the manufacturing of composites. The bubbles are carried if: (i) the pressure gradient is high enough, (ii) the surface tension of the liquid is low enough, (iii) the cross-sectional area of the channels in the reinforcement is sufficiently uniform. The theory reveals that the bubbles are more likely to be trapped on a small scale, i.e. within fiber bundles rather than on a large scale, i.e. between the bundles. It is also concluded that, if the bubbles are trapped at the resin flow front, a converging flow is better for the transport of the voids than a diverging flow.
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| 5. |
- Lundström, T. Staffan, et al.
(författare)
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In-plane permeability measurements on fiber reinforcements by the multi-cavity parallel flow technique
- 1999
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 20:1, s. 146-154
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Tidskriftsartikel (refereegranskat)abstract
- This report discusses the advantages and drawbacks of the multi-cavity parallel flow technique for permeability measurements. An experimental series with repeated measurements on material from the same roll shows that the repeatability of the technique is very good considering the manufacturing variability of the fabric. The measured standard deviation in the repeatability study is about 10%. It is, however, shown that the permeability can vary considerably- between reinforcements of similar geometry. Furthermore, computer simulations were used to estimate the errors when highly anisotropic materials are oriented at an angle to the material principal direction in the parallel flow technique. The conclusion based on the simulations is that the length to width ratio of the cavity should be larger than the anisotropy of the reinforcement for an acceptable error.
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| 6. |
- Sjögren, B.A., et al.
(författare)
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Failure mechanisms in polypropylene with glass beads
- 1997
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The effect of glass beads on the stress-strain behavior of isotactic polypropylene has been examined. Poisson's ratio and secant compliance as a function of strain have been measured. Both sets of data are consistent with interfacial debonding as the initial damage mechanism. Interfacial debonding is then followed by extensive plastic yielding of the matrix at the debond sites. The maximum stress and strain to failure decrease with glass bead content and glass bead diameter. Impact properties correlate with the ability of the composites to reach high strain to failure. The proposed failure mechanisms are supported by fractography and in-situ deformation studies by scanning electron microscopy.
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| 7. |
- Sjögren, B.A., et al.
(författare)
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Toughening mechanisms in rubber-modified glass fiber/unsaturated polyester composites
- 1999
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 20:5, s. 705-712
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Tidskriftsartikel (refereegranskat)abstract
- An important case of composite failure is the leakage of pipes and pressure vessels subjected to internal pressure. The primary damage mechanism leading to leakage is transverse cracking parallel to the fibers. Effects of matrix toughening on transverse cracking strains were therefore investigated for GF/UP cross-ply laminates with matrices of different liquid rubber content. The strain to the first transverse crack was increased from 0.2 to 0.6% with 10 wt% rubber. Debonding occurred at similar strains in GF/UP and GF/UP-rubber. However, whereas debonding was almost simultaneous with transverse cracking in GF/UP, gradual growth of debonds to short cracks took place initially in GF/UP-rubber. This was followed by slow extension of short cracks to a critical flaw size corresponding to unstable growth
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