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below.

Some mandrel is collapsible. Some of the mandrels are made from several parts which can be dismantled.

Some of them are made from a soluble plaster, which can be soaked in warm water to soften it, and then washed away with a powerful jet of water.

Some of the mandrel is made from a thin shell of metal, usually light alloy, which can be dissolved, in a dilute solution of warm alkali.

The mandrel made from a thin shell of electroplated nickel, acts as a permanent liner to which the composite is firmly bonded.

2.2.8 Pultrusion

This process represents a continuous transportation of fibre bundles through a resin matrix bath. The fibre along with the matrix resin bath is then dropped into a preheated die. After curing, the part is saw cut to desired length [20]. In this procedure continuous section of reinforced plastics is produced where the orientation of fibre is axial. The flow diagram of the Pultrusion process is shown in figure below.

Figure 2.8: Pultrusion [20]

With the help of the Pultrusion process, parts with complex shapes, such as tubings, channels, I-beams, Z-sections and flat bars manufactured. The Pultrusion process is equivalent to metal extrusion for metals. The only difference is that the part is pulled from the exit end of die in Pultrusion [20]

2.3 复合材料的测试-2.3 Testing of Composite Materials

Testing is done on composite materials to determine the behaviour of these composites. The designers make use of the information gathered from the testing to create structures which perform within the design requirements. The operations involved in the mechanical tests are as follows [10].

Quality control

Quality assurance

Comparisons between materials and selection

Design calculation

Predictions of performance under conditions other than those of the test

Indicators in materials development program

Some of the tasks cited in the above list might overlap and several are linked by lateral connections which become effective at various stages in the conversion of materials into end product. The property values obtained from a materials test depends on the state of internal order of the tested element. The state of internal order of many materials is subtle to the production route and other factors. The values obtained after the test must be regarded as relating just to it and not to the material in general. The material state variation is mainly in the atomic or molecular orders. After the processing stage the variation in material state slowly changes towards a state of greater order [10].

The molecular reordering generally occurs in the matrix and the fibre-matrix interface, in a fibre composite. The dominating source of variation is the spatial distribution of fibres. The variation is occurred during the manufacturing stage or is changed deliberately by the fabricator to induce a particular mechanical effect [10].

The number and range of applications for fibre-reinforced composite materials continues to rise day by day, as a result the need for new and enhanced test method also continues to increase. One area of continuing test method development is shear testing to measure the shear strength and shear moduli of composites. Shear te