Influence of the Processes Parameters on the Properties of The ...

Chapter 3.
Analytical Methods and Designs <strong>of</strong> Experiments
morphological closing can thus be used to fill small holes in <strong>the</strong> objects and to smooth <strong>the</strong> object contours.
An example is shown in Figure 3.16 (E) [Niemistö, 2006].
The morphological opening completes first erosion by <strong>the</strong> structural element and <strong>the</strong>n dilation by
<strong>the</strong> reflected structuring element. Erosion shrinks objects which can contain <strong>the</strong> structural element and
removes o<strong>the</strong>r objects. If some object is removed in erosion, it is not recovered in dilation. Opening
operation can be used to remove small foreground objects and to smooth <strong>the</strong> larger objects. The
morphological closing completes first <strong>the</strong> dilation and <strong>the</strong>n <strong>the</strong> erosion. Dilation expands all <strong>the</strong> foreground
objects and fills <strong>the</strong> background structure, if it is smaller than <strong>the</strong> structural element. Therefore <strong>the</strong> closing
operation can be used to fill small holes and to smooth <strong>the</strong> objects [Niemistö, 2006].
6 Macroscopic Methods
6.1 Mechanical Brazilian Tests
6.1.1 Principle <strong>of</strong> <strong>the</strong> Test
The direct testing <strong>of</strong> <strong>the</strong> tensile strength <strong>of</strong> brittle materials is very complex. Their disadvantage is
<strong>the</strong> low part <strong>of</strong> volume that is actually charged with <strong>the</strong> load and <strong>the</strong> strong dependency <strong>of</strong> <strong>the</strong> samples
surface and <strong>the</strong>ir dimensions. Brazilian Test is an indirect measure <strong>of</strong> <strong>the</strong> tensile strength and <strong>the</strong> resistance
to uniaxial tensile loads without yielding or fracture <strong>of</strong> brittle materials. The equipment comprises:
A loading frame, 25 kN capacity, having a base and a cross head joined toge<strong>the</strong>r with two solid
pillars with nuts. At <strong>the</strong> top, <strong>the</strong> pillars have long threads for height adjustment. On <strong>the</strong> base, a 25
kN hydraulic jack is controlled by a computer. This jack has an integral pumping unit and oil
reservoir. A 25 kN capacity pressure gauge is fixed to <strong>the</strong> jack for indicating <strong>the</strong> load on <strong>the</strong>
specimen (cf. Figure 3.17).
Figure 3.17: H25KS Brazilian testing equipment.
A Brazilian specimen, cylinder with approximately thickness half <strong>the</strong> diameter or at least 2 mm.
The sample was clamped into two jaws <strong>of</strong> <strong>the</strong> machine.
Fairhurst [1964] and Wijk [1978] looked at <strong>the</strong> validity <strong>of</strong> <strong>the</strong> method from a <strong>the</strong>oretical
perspective and favoured this method to that <strong>of</strong> <strong>the</strong> point-load test. Clarke [1992] found that <strong>the</strong> crack
initiates in <strong>the</strong> centre <strong>of</strong> <strong>the</strong> specimen and that stress concentrations built up around <strong>the</strong> loading plates
effectively hindering crack propagation in that area. Yu et al. [2006] have investigated <strong>the</strong> method both
practically and <strong>the</strong>oretically and have concluded that results given by <strong>the</strong> two methods are comparable. The
method <strong>of</strong> breakage is well documented and has <strong>the</strong> term ‘hourglasses’ associated with it.
This leads to <strong>the</strong> special advantages, summarized as follows:
Simple sample geometry low effort, cost reduction.
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