Editing Composite material (section)

==Cores in composites==
Several layup designs of composite also involve a co-curing or post-curing of the prepreg with many other media, such as foam or honeycomb. Generally, this is known as a [[sandwich structured composite|sandwich structure]]. This is a more general layup for the production of cowlings, doors, radomes or non-structural parts.

Open- and closed-cell-structured [[foam]]s like [[polyvinyl chloride]], [[polyurethane]], [[polyethylene]], or [[polystyrene]] foams, [[balsa|balsa wood]], [[syntactic foam]]s, and [[composite honeycomb|honeycombs]] are generally utilized core materials. Open- and closed-cell [[metal foam]] can also be utilized as core materials. Recently, 3D [[graphene]] structures ( also called graphene foam) have also been employed as core structures. A recent review by Khurram and Xu et al., have provided the summary of the state-of-the-art techniques for fabrication of the 3D structure of graphene, and the examples of the use of these foam like structures as a core for their respective polymer composites.<ref>{{cite journal |last1=Shehzad |first1=Khurram |last2=Xu |first2=Yang |last3=Gao |first3=Chao |last4=Duan |first4=Xiangfeng |title=Three-dimensional macro-structures of two-dimensional nanomaterials |journal=Chemical Society Reviews |date=2016 |volume=45 |issue=20 |pages=5541–5588 |doi=10.1039/c6cs00218h |pmid=27459895}}</ref>

===Semi-crystalline polymers===
Although the two phases are chemically equivalent, semi-crystalline polymers can be described both quantitatively and qualitatively as composite materials. The crystalline portion has a higher elastic modulus and provides reinforcement for the less stiff, amorphous phase. Polymeric materials can range from 0% to 100%<ref>{{cite journal |last1=Agbolaghi |first1=Samira |last2=Abbaspoor |first2=Saleheh |last3=Abbasi |first3=Farhang |title=A comprehensive review on polymer single crystals—From fundamental concepts to applications |journal=Progress in Polymer Science |date=June 2018 |volume=81 |pages=22–79 |doi=10.1016/j.progpolymsci.2017.11.006 }}</ref> crystallinity aka volume fraction depending on molecular structure and thermal history. Different processing techniques can be employed to vary the percent crystallinity in these materials and thus the mechanical properties of these materials as described in the physical properties section. This effect is seen in a variety of places from industrial plastics like polyethylene shopping bags to spiders which can produce silks with different mechanical properties.<ref>{{cite journal |last1=Termonia |first1=Yves |title=Molecular Modeling of Spider Silk Elasticity |journal=Macromolecules |date=December 1994 |volume=27 |issue=25 |pages=7378–7381 |doi=10.1021/ma00103a018 |bibcode=1994MaMol..27.7378T }}</ref> In many cases these materials act like particle composites with randomly dispersed crystals known as spherulites. However they can also be engineered to be anisotropic and act more like fiber reinforced composites.<ref>{{cite journal |last1=Quan |first1=Hui |last2=Li |first2=Zhong-Ming |last3=Yang |first3=Ming-Bo |last4=Huang |first4=Rui |title=On transcrystallinity in semi-crystalline polymer composites |journal=Composites Science and Technology |date=June 2005 |volume=65 |issue=7–8 |pages=999–1021 |doi=10.1016/j.compscitech.2004.11.015 }}</ref> In the case of spider silk, the properties of the material can even be dependent on the size of the crystals, independent of the volume fraction.<ref>{{cite journal |last1=Keten |first1=Sinan |last2=Xu |first2=Zhiping |last3=Ihle |first3=Britni |last4=Buehler |first4=Markus J. |title=Nanoconfinement controls stiffness, strength and mechanical toughness of β-sheet crystals in silk |journal=Nature Materials |date=14 March 2010 |volume=9 |issue=4 |pages=359–367 |doi=10.1038/nmat2704 |pmid=20228820 |bibcode=2010NatMa...9..359K }}</ref> Ironically, single component polymeric materials are some of the most easily tunable composite materials known.