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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

Relative volumetric

Relative volumetric compression c iso ( ) Rel. volumetric compression c iso 0.6 0.5 0.4 0.3 0.2 0.1 FATO TOPC10 0.0 0.1 1 10 100 Isostatic pressure P (MPa) iso Isostatic pressure P iso /MPa Figure 4.35 Isostatic compression of the TOPC10 and FATO preforms. The TOPC10 preform with the lowest compression strength σc in the uniaxial test (0.7 MPa) started to compress significantly in the isostatic test at a pressure of 1 MPa. At the maximum load, the compression reached 0.34 and after pressure release to ambient, a constant compression of 0.25 was measured. Isostatic pressure P (MPa) iso iso /MPa 12 10 8 6 4 2 0 0.0 0.1 0.2 0.3 Relative Rel. volumetric compression c ciso() iso 129 AOPC20 AGPC15 TOPC10 TOPC20 MOPC20 FATO Figure 4.36 Isostatic pressure as a function of the compression in the range of 0.1 MPa to 10 MPa.

The volumetric stiffness Eiso of the preforms in the isostatic compression mode was evaluated as the slope of the linear region in the pressure range of 0.1 to 10 MPa, Figure 4.36. Table 4.3 Characteristic parameters of isostatic compression test of preforms. Volumetric stiffness E iso MPa Compression at 100 MPa c iso,100 130 Maximum compression c iso,max Permanent compression c iso,per AOPC20 68 0.30 0.34 0.27 AGPC15 261 0.28 0.34 0.24 TOPC10 92 0.29 0.34 0.25 TOPC20 71 0.26 0.32 0.27 MOPC20 921 0.28 0.36 0.29 FATO 31 0.40 0.46 0.42 The slopes of the curves were calculated and the values are presented in Table 4.3. The lowest value was that of FATO (31 MPa) whereas MOPC20 exhibited a stiffness of 921 MPa. That of TOPC20 and AOPC20 were similar to each other and are between the stiffness of TOPC10 and FATO. The values of the compression ciso,max reached at the maximum isostatic pressure of 212 MPa are listed in Table 4.3. The permanent compressions after pressure release (ciso,per) and the compressions at 100 MPa (ciso,100) are reported. The pressure of 100 MPa was the maximum isostatic melt pressure applied in the constant flux metal melt infiltration experiments. 4.6.4 Preform permeability The permeability of the preforms was measured by passing pressurized water through them and the influence of water pressure assessed by varying the pressure in the range of 0.05 MPa to 0.25 MPa. The maximum deviation of a series of 3 measurements at each pressure point was ± 5%. The test at the highest pressure (0.25 MPa) resulted in fracture of the TOPC10 preforms, indicating that the maximum shear strength of the wet sample had been reached.

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