quiz 1

PPE is not optional when working with composites [1, 2].

The same type of gloves will not always be appropriate, so it is important to ensure that the equipment is well-stocked [3]. The material selected for protective gear is determined by the hazards involved [4, 5].

There are four routes of exposure [6]:

• Absorption can happen through the eyes, hands, and skin [5, 7]. To protect the skin, clothing, and possibly a Tyvek suit or apron, should be worn [4]. Safety glasses and face shields protect the eyes [3]. Gloves protect the hands [3].

• Inhalation is breathing a substance into the lungs [6]. Respirators can be used for protection [4, 8].

• Injection introduces foreign material into the bloodstream or tissue [6]. Attention to the task, avoiding rushing, and having proper first aid supplies are key to preventing injection [8, 9].

• Ingestion is swallowing chemicals, which can occur if chemicals are left on hands, clothing, or beards, or through contaminated food, drinks, or cigarettes [10]. To prevent this, there should be no food in the lab, gloves should be removed before drinking or eating, and hands should be washed thoroughly and often [8].

Adhesive bonding is a process that transfers loads between substrates and has the ability to transfer loads more efficiently [11, 12]. Long term durability requires proper surface preparation, the right adhesive, uniform bondline thickness, uniform clamping, and proper cure [11]. Fastening involves loads transferred at the fastened joint [11].

Co-curing is curing the laminate while simultaneously bonding it to some other uncured structure, or to a core material such as honeycomb, foam, or end-grain balsa, and involves curing in one process [13, 14]. Co-bonding is curing together of two or more elements where at least one has already been fully cured and one is uncured, and requires meticulous surface preparation [14, 15]. Secondary Bonding involves two or more pre-cured or already cured composite parts joined together by adhesive bonding [13, 14]. The only chemical or thermal reaction is the curing of the adhesive joining the parts and requires precise tooling to control location of mating parts [13].

Surface preparation for bonding to a fiber reinforced plastic surface depends upon chemical attachment and attraction and sharing of electrons at the interface Covalent bond [16, 17]. The process to prep metal for bonding includes chemical pretreatments to remove the oxidized layer of metal and etching a mechanical micro-surface into the exposed metal-oxide layer [16, 17]. To ensure the surface free energy value is high enough for bond that coalent bond to actually maintain itself, the material must be bonded, bagged, and under vacuum literally within a half hour from completion of the etching process [18, 19].

For mechanical fastening of thick composites, use large diameter fasteners with high bearing strength and an interference fit [20, 21]. Large-head, expanded sleeved fasteners and stainless steel sleeves are also used which expand diametrically inside the hole as the titanium fastener body is drawn through it [20, 21]. Bonding of thin composites is preferred over mechanical fastening [22, 23].

For drilling carbon and glass fiber reinforced composites, carbide drills with a positive or extreme rake angle, fine chisel edge, and gradual taper up to final diameter should be used [24-26]. Diamond coated carbide drills are also highly effective for carbon fiber and fiberglass because small diamond bits are deposited on the cutting edge and embedded in a metal matrix material [24, 26, 27]. For drilling aramid fiber reinforced composites, a brad –point twist drill (self-centering, modified, two-flute twist drill with a sharp center point surrounded by two sharp peripheral cutting edges) should be used [26, 27].