| 1. |
- Al-Maqdasi, Zainab, 1986-, et al.
(författare)
-
Time-dependent properties of high-density polyethylene with wood/graphene nanoplatelets reinforcement
- 2023
-
Ingår i: Polymer Composites. - : John Wiley & Sons. - 0272-8397 .- 1548-0569. ; 44:1, s. 465-479
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of graphene nanoplatelets (GNPs) on the long-term performance of wood fiber/high-density polyethylene (HDPE) composite is investigated by using short-term creep tests with an efficient, faster data analysis approach. Previously, it was shown that the addition of GNPs at 15 wt% into HDPE reduces the viscoplastic (VP) strain developed during 2 h creep by ~50%. The current study shows that 25 and 40 wt% wood content in HDPE reduce the VP strains developed during 2 h creep time by >75% with no noticeable effect of the increased wood content. However, further addition of GNPs results in more than 90% total reduction in the VP strains. The current study shows that the development of the VP strains in the hybrid composites follows Zapas model. Viscoelastic (VE) response of these composites is nonlinear and thus is described by Schapery's model. Parameters for VP and VE models are obtained from the creep experiments and were validated in a separate loading-unloading test sequence. Results show a very good agreement between experiments and predictions for the studied materials as long as the micro-damage is not present.
|
|
| 2. |
- Almgren, Karin M., et al.
(författare)
-
Contribution of wood fiber hygroexpansion to moisture induced thickness swelling of composite plates
- 2010
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 31:5, s. 762-771
-
Tidskriftsartikel (refereegranskat)abstract
- One of the main drawbacks of wood fiber-based composite materials is their propensity to swell due to moisture uptake. Because the wood fibers are usually the main contributor to hygroexpansion, it is of interest to quantify the hygroexpansion coefficient of wood fibers, to compare and rank different types of fibers. This investigation outlines an inverse method to estimate the transverse hygroexpansion coefficient of wood fibers based on measurements of moisture induced thickness swelling of composite plates. The model is based on composite micromechanics and laminate theory. Thickness swelling has been measured on polylactide matrix composites with either bleached reference fibers or crosslinked fibers. The crosslinking modification reduced the transverse hygroexpansion of the composites and the transverse coefficient of hygroexpansion of the fibers was reduced from 0.28 strain per relative humidity for reference fibers to 0.12 for cross-linked fibers
|
|
| 3. |
- Almgren, Karin M., et al.
(författare)
-
Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials
- 2009
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:12, s. 1809-1816
-
Tidskriftsartikel (refereegranskat)abstract
- Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA-modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out-of-plane hygroexpansion of PLA and PLA/PP composites, under water-immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA-modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out-of-plane hygroexpansion, with a high-fiber fraction leading to large hygroexpansion. Fiber-matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 30:1809-1816, 2009.
|
|
| 4. |
- Alsalmah, Hessa A., et al.
(författare)
-
Synthesis and characterization of PEG/CS-AgNO3 polymer nanocomposites for flexible optoelectronic and energy storage applications
- 2024
-
Ingår i: Polymer Composites. - : WILEY. - 0272-8397 .- 1548-0569.
-
Tidskriftsartikel (refereegranskat)abstract
- The Polyethylene glycol (PEG) and Chitosan (CS)/silver nitrate (AgNO3) thin films were prepared by utilizing the casting technique to enhance their optical, dielectric, and electrical properties. Their physicochemical characteristics were investigated using a variety of techniques. The FT-IR study demonstrates that the addition of AgNO3 NPs results in a discernible difference in the intensities and locations of vibrational peaks of all bands, supporting the incorporation of AgNO(3)NPs inside the PEG/CS. The XRD analysis indicates that the peak at 2 theta = 23.1(degrees) broadens and strengthens proportionally with the increase of AgNO3 NPs. This observation suggests that the incorporation of AgNO3 NPs into PEG/CS results in a greater degree of amorphous characteristics compared to the PEG/CS blend. Additionally, when the amount of AgNO3 NPs increases in the PEG/CS, the energy band gap decreases, resulting in the creation of localized states between the valence and conduction bands. These polymer nanocomposite films' electrical conductivity, dielectric constant, and dielectric loss all increased with frequency increased and showed variance for various composite concentrations. These AgNO(3)NPs/PEG/CS films can be promising options for frequency-tunable nanodielectrics, flexible dielectric substrates, and bandgap-regulated materials for upcoming microelectronic, capacitive energy storage, and optoelectronic technologies, according to the experimental results.
|
|
| 5. |
- Andersons, Janis, et al.
(författare)
-
Progressive cracking mastercurves of the transverse ply in a laminate
- 2009
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:8, s. 1175-1182
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using the results of a probabilistic cracking model, approximate relations for crack density as a function of stress are derived for initiation-controlled and propagation-controlled cracking. It is shown that the crack density evolution in the transverse ply can be represented by a mastercurve in suitably normalized coordinates. The mastercurve approach is applied to progressive cracking in glass/epoxy laminates.
|
|
| 6. |
- Andersons, J., et al.
(författare)
-
Stiffness and strength of flax fiber/polymer matrix composites
- 2006
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 27:2, s. 221-229
-
Tidskriftsartikel (refereegranskat)abstract
- Flax fiber composites with thermoset and thermoplastic polymer matrices have been manufactured and tested for stiffness and strength under uniaxial tension. Flax/polypropylene and flax/maleic anhydride grafted polypropylene composites are produced from compound obtained by coextrusion of granulated polypropylene and flax fibers, while flax fiber mat/vinylester and modified acrylic resin composites are manufactured by resin transfer molding. The applicability of rule-of-mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers is considered.
|
|
| 7. |
- Andersson, H.M., et al.
(författare)
-
Application of digital speckle photography to measure thickness variations in the vacuum infusion process
- 2003
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 24:3, s. 448-455
-
Tidskriftsartikel (refereegranskat)abstract
- A new method to measure the movement of the flexible bag used in vacuum infusion is presented. The method is based on an in-house developed stereoscopic digital speckle photography system (DSP). The advantage with this optical method, which is based on cross-correlation, is that the deflection of a large area can be continuously measured with a great accuracy (down to 10 μm. The method is at this stage most suited for research but can in the long run also be adopted in production control and optimization. By use of the method it was confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. The existence of the ditch demonstrates that the stiffness of the reinforcement can be considerably reduced when it is wetted. Hence, the maximum fiber volume fraction can be larger than predicted from dry measurements of preform elasticity. It is likely that the overall thickness reduction after complete filling emanates from lubrication of the fibers combined with an outflow of the resin. Besides, the cross-linking starts and the polymer shrinks. Hence, the alteration in height will continue until complete cross-linking is reached.
|
|
| 8. |
- Andersson, Magnus, et al.
(författare)
-
Computational fluid dynamics applied to the vacuum infusion process
- 2005
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 26:2, s. 231-239
-
Tidskriftsartikel (refereegranskat)abstract
- An all-purpose computational fluid dynamics software is used for simulations of the vacuum infusion process. The study comprises simulations of a full three-dimensional two-phase flow through a porous medium. The medium that has an anisotropic, spatial- and time-dependent permeability is located in a complex mold with moving boundaries. With this generalization, different material combinations, processing conditions, and even other manufacturing techniques can be evaluated. The strength of the presented approach is exemplified by simulations of mold filling of a real part, using a typical vacuum infusion set-up. In addition to the overall development of the model, a number of specific aspects and phenomena are investigated and evaluated. Local lead of the flow front and a minor influence in overall flow front lead-lag, with no influence on the fill time, is the result of simulations of edge effects due to poor preform fitting.
|
|
| 9. |
- Andersson, Magnus, et al.
(författare)
-
Flow-enhancing layers in the vacuum infusion process
- 2002
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 23:5, s. 895-901
-
Tidskriftsartikel (refereegranskat)abstract
- The current trend towards increased use of vacuum infusion molding for large surface-area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow-enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through-thickness flow front was observed by making a number of color marks on the glass-mats forming the reinforcing stack, which became visible when the resin reached their position. The in-plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill-time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead-lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead-lag has a miximum close to the inlet.
|
|
| 10. |
- Asp, Leif, et al.
(författare)
-
Prediction of failure initiation in polypropylene with glass beads
- 1997
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 18:1, s. 9-15
-
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
|
|
