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There is sometimes a big gap between simulation and real life, this is obvious when you compare the first proposed virtual shape of the Shoulder Pads (after mentioned as SP) to the current real one.
After extracting shoulder 3D shape and after mould printing (see previous article on the subject), the logical suite of this work was to effectively create these in real life : there you can find a brief description of the shoulder pad manufacturing process.
Before getting in the manufacturing process for the Hard Upper Torso (HUT) resistant SP, let’s give a quick summary of the materials used in these and their functions. There are three parts:
An external layer composed of heavy anti-abrasive fabric called Cordura (c) which is primarily used for sports with potential high abrasion e.g. Karting.
An outer layer (supposed to bear HUT weight) with the fiberglass outer layer (300+300+100 = 700 g/m2) and 2cm foam is in contact with the HUT (below external layer) and is the first load spreader over a smooth surface as shown in the images above.
A comfort layer including a fiberglass comfort layer (300+300+100 = 700 g/m2) plus 1cm foam : it has been designed to be a second skin, to perfectly fit the shoulder of the wearer. His principal function is to spread the strength coming from the HUT.
Comment: the simulation was first made over a shoulder shape, so it has been a static one, but during the suit’s use, it has been confirmed that some parts of the SP where interfering with normal tester’s movements. That kind of problems deal with dynamic ergonomics, it has been solved by conceiving a soft comfort layer (200 g/m2) and putting it directly on the shoulder of the suit tester during use. The parts bended during movement were marked during the experiment and simply withdrawn afterwards. At this point we had the final shape of the SP.
The manufacturing itself including different testing types begins there; the first step is to lay fiberglass over the moulds.
In order to manufacture the SP properly we had to perfectly master the fiberglass laying process, Marc Rodriguez in charge of this project has a textile background (Textile engineer student) and was able to perform tests in the field. The main issue was to bear the HUT’s weight and so resistant layers had to be used. After testing different fabric weights and weavings, it has been decided to use a soft tissue enclosed in two heavy fabrics all in plain waving. This is because resin must fill the vacuum spaces at the interface between the fabrics to assure cohesion and so, resistance. Tests have been performed between two heavy fabrics but the resin does not totally fill the holes leading to layers’ separation after drying.
Many laying techniques are now available and so we had to choose. The simplest one when talking about multilayer fiberglass has been found on this site: www.sierratel.com/jerico/method2.html. It consists of an initial horizontal laying with resin spreading after each laid sheet (to avoid air intrusion) followed by a waiting time depending on the resin’s/hardener’s chemical interactions called “gel time”, namely the time necessary to avoid any resin dripping from the fabrics. The final step is to put this multilayer material on top of the desired mould giving its final shape to it. The complete resin’s polymerization takes effect after few hours then and the hard layer is ready to use.
Following these considerations around fiberglass, comes the interface question between different materials : foam and fiberglass fabric. We had to find the best glue to stick these in dynamic conditions, so we made different tests beginning with plastic glue and super glue, but that led to poor results.
We discovered that simple duct tape is the best material for sticking, avoiding slipping and assuring high contact strength; furthermore, it allows reuse of hard layers even after the foam deteriorates.
The different layers have so been taped after assuring perfect cohesion between them and especially around the acromion area considered as an uneven surface compared to the rest of the layer.
Last but not the least we create a pattern for cutting the external fabric layer in order to provide an anti-abrasion layer for the SP. This has first been done theoretically by flattening the 3D model of the SP (3D solid), using Blender (c) with his “unwrap” function after exporting the 3D solid to a mesh (“.stl” format). The pattern has then been printed and the fabric cut to its bounds.
There is finally the sewing part and the final integration inside Aouda.X, these subjects will perhaps be inserted in future articles.
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