Composites part 1 - c

Question 1

What is roving?

Answer 1

A bundle of continuous filaments. The bundle may be in the form of an untwisted strand or twisted yarn. The roving is available in a range of weights or ‘tex’; weighed in grams per kilometer.

Question 2

What is chopped strand mat (CSM)?

Answer 2

This is a sheet of reinforcement material comprised of randomly dispersed chopped fibers (usually 25-50 mm in length) held together with a resinous binder. CSM is produced in a variety of widths, lengths and weights.

Question 3

What is woven fabric? Explain weft and warp?

Answer 3

This is produced from yarns. Woven fabrics are described by the weave pattern; the number of yarns in warp and weft and the yarn count. In weaving the weft is the term for the yarn which is drawn through the warp to create cloth. Warp is the lengthwise or longitudinal thread in a roll, while weft is the transverse thread.

Question 4

What is a plain weave?

Answer 4

The simplest form with warp and weft yarns alternatively passing under and over each other.

Question 5

What is a balanced weave?

Answer 5

The number and count of warp and weft yarns are equal.

Question 6

What is a satin weave?

Answer 6

Each warp and weft yarn goes over one yarn then under a number of yarns. Made by floating a yarn over 4+ yarns then under one yarn.

Question 7

What are the advantages of satin weave?

Answer 7

Makes a very smooth, shiny and drapable fabric.

Question 8

What are the disadvantages of satin weave?

Answer 8

Not durable, floats tend to break or snag.

Question 9

What does a 5-harness satin weave have?

Answer 9

One warp yarn passing over 4 weft yarns before passing under the fifth yarn.

Question 10

What is a twill weave?

Answer 10

One in which the warp and weft yarns which pass over each other are varied, recognizable by diagonal lines.

Question 11

What does a 2x2 twill weave have?

Answer 11

2 over by 2 under.

Question 12

Why are satin and twill weaves more suitable for moulding complex curvatures than plain weaves?

Answer 12

Because they have better drape characteristics.

Question 13

What is woven roving?

Answer 13

Coarse heavy weight woven fabric produced from strand rovings. A range of filament diameter, no of strands and weave styles are available. Plain weave woven roving is the most common. Tapes are usually woven in a variety of weave styles and widths, normally less than 150mm.

Question 14

How are knitted fabrics produced?

Answer 14

Produced using conventional textile knitting processes. Using modern computer controlled knitting machines the process is capable of producing a variety of patterns and shapes at high rates of production.

Question 15

Why are knitted fabrics more pliable than woven?

Answer 15

Because they don’t have any crimped fibers.

Question 16

Why do knitted fabrics have to be tailored to individual customer requirements?

Answer 16

Because there is a wide variety of yarn orientations and fabric weights

Question 17

What are the disadvantages of knitted fabrics?

Answer 17

• The reinforcement materials are easily damaged by the process
• The high proportion of looping in the resulting fabrics lead to poor mechanical properties.

Question 18

What type has a greater strength to weight ratio: woven or braided fabric?

Answer 18

Braided

Question 19

Why are braided fabrics more expensive than woven fabrics?

Answer 19

Because of its complex manufacturing process. However, manufacturing costs have decreased making braided fabrics more cost-competitive.

Question 20

Where do braided fabrics get their strength?

Answer 20

From intertwining three or more yarns without any two yarns being twisted around each other, continuously woven on the bias so that at least one axial yarn is not crimped. This arrangement distributes the load efficiently throughout the braid.

Question 21

What configurations do braids come in?

Answer 21

Flat or tubular

Question 22

What are flat braids used for?

Answer 22

Selective reinforcement, such as strengthening specific areas in pultruded parts.

Question 23

What are tubular cross sections used in?

Answer 23

Tubular braid can be pultruded over a mandrel, producing hollow cross sections for use in windsurfer masts, lamp and utility poles, and other parts.

Question 24

What is non-crimp fabric?

Answer 24

Continuous reinforcement, usually roving, laid in planar form in straight lines usually at some specified angle to the weft direction and is held together with a light weight warp or linking yarn (knit)

Question 25

Why can non-crimp fabric drape into complex shapes?

Answer 25

The absence of reinforcement loops reduces kink stresses and allows the fabric to shear easily and therefore drape into complex shapes.

Question 26

What varieties of non-crimp fabrics can you get?

Answer 26

Unidirectional, biaxial, triaxial, etc.

Question 27

What are tissues, felts and veils?

Answer 27

Very lightweight, random reinforcement mats primarily used to improve the surface appearance of mouldings.

Question 28

Where are tissues, felts and veils typically placed?

Answer 28

either between the gel coat (if used) and the heavier laminating reinforcement, or as the final lamination to block out the fiber pattern of the underlying reinforcement and provide smooth surface finish.

Question 29

What is a hybrid?

Answer 29

A hybrid is a reinforcement, with two or more different types of fiber or fiber form to achieve cost and/or performance benefits/

Question 30

What are the 2 distinct categories of hybrid?

Answer 30

1. combination laminates

2. mixed fibers