Glass fibres short

A composite material for a car-repair kit consists of a random mixture of short glass fibres in a polyester matrix. Estimate the maximum toughness of the composite. You may assume that the volume fraction of glass is 30% the fibre diameter is 15 pm the fracture strength of the fibres is 1400 MPa and the shear strength of the matrix is 30 MPa. 

SRIM or SRRIM - structural (reinforced) reaction injection moulding - mats or fabrics are placed in the mould before injection of the resin, possibly reinforced with short glass fibres. 

Depending on the rigidity and the ductility of the matrix, when a stress is applied to a short glass fibre reinforced composite the following steps can be observed ... 

Modelling of a real case reinforcement of PA 66 with short glass fibres... 

Short glass fibre reinforcement the main thermoplastics are offered in such grades. Some short carbon or aramid fibre reinforced resins are also marketed. 

The short glass fibre reinforced grades are used for all sorts of injected parts. 

Figure 6.8 plots the reinforcement ratios for short glass fibre reinforced polyamide (PA-GF) versus neat polyamide for six important characteristics calculated versus density and material cost. These characteristics are tensile strength, tensile and flexural modulus, impact strength, HDT A and B. 

Figure 6.8. Fibres examples of reinforcement ratios for short glass fibre reinforced PA 6...

Effect of short glass fibres on material cost... 

Figure 6.9 shows examples of cost ratios (costs of short glass fibre reinforced thermoplas-tics/costs of the neat thermoplastics) versus costs of the neat grades. 

As for glass fibres, reinforcement with continuous fibres leads to the highest performances. Compared to short glass fibres, short carbon fibres yield higher reinforcement ratios for the modulus and tensile strength but the impact strength decreases. 

Table 6.9 Examples of enhancement ratios obtained with incorporation of short aramid fibres instead of short glass fibres in a thermoplastic composite...

Table 6.31 shows the properties of the same thermoplastic reinforced with increasing levels of the same short glass fibre. 

Table 6.32 shows some basic property examples of short glass fibre reinforced thermoplastics. In some cases the glass fibres can be combined with mineral fillers. 

Table 632 Property examples of short glass fibre reinforced thermoplastics...

Grades reinforced with fibres 20 mm and more in length cannot be processed on conventional equipment. It is necessary to use, for example, the extrusion-compression technique. The process differs too much from conventional injection used for short glass fibre reinforced thermoplastics to measure the influence of fibre length alone. 

Borealis has developed a high-performance short glass fibre reinforced polypropylene (HPGF) family that has the technological and economical potential to replace long glass fibre (LFRT) in highly stressed parts for technical automotive applications. 

Table 7.2 shows the properties of an HPGF (Xmod GB305HP) containing 35% short glass fibres compared to LFRT polypropylene. 

HPGF High-Performance short Glass Fibre reinforced polypropylene... 

The blending of short glass fibres results in an increase of the E-modulus to e g. its threefold over the whole temperature region. If the slope of the log E - T curve is small, such as with semi-crystalline polymers between Tg and T, a vertical shift causes a considerable horizontal shift (see MT 8.1.2.), so a strong increase of the softening points, which are of importance in applications at higher temperatures. 

A higher stiffness is also obtained by the incorporation of hard particles or short fibres. Particles are responsible for a 2 to 2.5 fold increase in E, while with short glass fibres a factor of 3 to 5 can be obtained. Long fibres, forming a continuous reinforcing phase, produce a much stronger effect here the fibres practically carry the whole stress, while the matrix polymer has hardly any influence on the stiffness. 

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