/ by Aldo Avancini /

A look at 2 composite materials.

Recently there has been greater interest (for the time being relating to information only) on the problems regarding the structural use of two composite materials: fibreglass and carbon fibre. The former is commonly used (albeit not for structural purposes), the latter on the other hand is expensive and is used for very specific applications.

Given that “composite materials” are identified as materials made fro several components that remain separate from each other, fibreglass can be imagined as fibres with different arrangements ‘locked’ together by a chemical resin, with the main task of ensuring rigidity and strength. The resulting material offers mechanical and other characteristics that are far superior to those offered by the individual materials separately, which would be more fragile and show an almost linear response until the point of breakage.

To be more clear, it should be remembered that dynamic analysis can define the stresses generated on a material, and laboratory instruments can be used to identify the structural capacity of the material to withstand such stresses. Acceptance of a standard production component however also and above all is the result of the work of several operators. 

First of all, defects can be divided into those due to production (mainly due to non-uniformity of resin thickness, for example, moulds with bumps and depressions, and inclusion of foreign bodies including the air) from those during operation (essentially linked to to delamination, free fibres, surface breakage due to impact, and so on).

All of this can be broken down into two fundamental questions.

The first can simply be identified as manufacturing reliability, that is, how confident can we be about the laboratory/sampling results. In this stage, manufacturers provide specific samples of fibreglass with a controlled thickness, and these are compared against samples of fibreglass cut from standard production items. These two groups (specific production lot and normal production) should not show significant inconsistencies between them, nor between samples from the same lot.

The next question concerning instrumental testing methods is much more important, in order to verify that the manufactured product has the desired mechanical characteristics.

Following the typical basic tests (visual, unit weight, thickness, cross-linking…) what other tests can be done? Penetrating liquids? Magnetic? Ultrasound? X-rays?

It is clear that these proposals may be provocative. However how can the mechanical values based on calculations be considered based on destructive testing? One technology highlights only ‘open’ problems that are clearly present in the object; others require a magnetisable environment, others transmissibility, compactness, a substantially constant density and so on.

Taken from Games&Parks Industry February 2019, page 84

Ing. Aldo Avancini /  Proposta Srl / proposta_design@yahoo.it