Question

Q.C8 (a) Discuss the importance of resin viscosity in composite manufacture and in particular optimisation of the wet lay-up/vacuum bag process. (refer to it in comparison of composite manufacture using prepreg) (10 marks) (b) Discuss the advantages of on-line cure monitoring of composites during manufacture (5 marks) (c) Where can the traces of voids be traced to in composite manufacturing and comment on the effect voids will have on composite performance. (5 marks)

Answer 1

(a) Importance of resin viscosity in composite manufacture -

High viscosity epoxy resins display attributes, for example, temperature obstruction; both low and high, great synthetic opposition, an incredible attachment to an assortment of substrates, for example, plastics, wood, and composites. They are regularly utilized for castings or shape just as in the assembling of water skis and snowboards.

Medium viscosity items have been utilized widely in the assembling procedure of skis, snowboards, wakeboards and oars. The vast majority of them are uniquely intended for use in warmed pressure shaping applications. They are portrayed by characteristics, for example, lucidity, high quality and reactivity, and improved wet lay-up procedures. At the point when combined with our amine hardeners, these items exhibit superb low temperature, flexural, effect and bond properties.

Low viscosity epoxy resins show characteristics, for example, magnificent bond, remarkable wetting properties, extraordinary synthetic opposition, and elite on troublesome substrates. These plans can be utilized for an assortment of utilization.

Optimisation of the wet lay-up/vacuum bag process.
The wet lay-up strategy is streamlined by joining an abide period toward the beginning of the fixed cycle to build the gum consistency before applying the packing prßsure. Pitch thickness is the parameter in delivering fibre composites with low void substance and a stay time 'window ' exists for every tar framework inside which excellent overlays can be reliably created with up to 58% fibre volume division and under 2% voidage.

It is broadly viewed as that wet layed-up carbon fibre epoxy composites manufactured by vacuum stowing experience the ill effects of an inalienably high void substance contrasted with autoclaved prepreg frameworks, and undoubtedly can achieve 10% or above now and again. One explanation behind this is the vacuum pack union generally utilized is to a great extent completed without respect to the consistency of the sap frameworks being utilized.

(b) Advantages of on-line cure monitoring of composites during manufacture.

(i) Unlike the other processes, this process is non-destructive in nature.

(ii) With high precision, monitoring can be done.

(iii) For predicting the end state of the material, online and in situ process is used.

(iv) It provides high sensitivity.

(v) Better reliability.

(c)

In composite manufacturing, voids can be traced on the material surface.

Effects of Voids on Composite Performance-

Voids are dependably the potential areas of disappointment and cause brokenness in the material properties of CFRP, which corrupt the mechanical exhibition of CFRP. The loss of mechanical properties can happen in all CFRP structures and will in general increment in recurrence with basic unpredictability. The impact of voids on the mechanical properties of CFRP items has been the subject of numerous examinations for quite a few years. The mechanical properties of CFRP items are generally characterized into two gatherings in the wake of contemplating the way that CFRP materials are a mix of fibre and lattice. One gathering comprises of fibre-overwhelmed mechanical properties and another gathering incorporates grid commanded ones. With respect to voids, numerous investigations brought up that fibre-commanded mechanical properties were not essentially affected by the void nearness, while framework overwhelmed properties were emphatically reliant on their existences. This is somewhat because of the way that CFRP items are extremely touchy to push fixation and voids, shockingly, impact pressure dissemination in CFRP items and lead to pressure focus, which at long last results in a neighbourhood disappointment.