M.Sc Student | Eitan Nadav |
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Subject | Effect of Grain Morphology on Mechanical failure of Pressed Material |

Department | Department of Mechanical Engineering |

Supervisor | Professor Emeritus Eli Altus |

Full Thesis text - in Hebrew |

The aim of this study is to understand, predict and improve the mechanical properties of pressed materials by controlling pressure profile parameters and grain size.

Effect of grains morphology of HV-10 on the mechanical properties such as Maximum Stress and its Strain, and maximum stiffness was studied by using Brazilian Test Specimens in four aggregate size ranges: 1700?2300 , 850?1700 , 300?850 , and 150?300 ?m . and three bi-modal mixings using the two extreme groups with ratios of 1:1, 1:3, and 3:1. The free density of the powder from each group was measured. Furthermore, Final density of specimens was measured.

Disc like specimens (Ø20x8mm) were cut from the crude material. Several specimens were polished and some grains and disks were binder dissolved to obtain better microscopic images. Some grains were taken for analysis using the Image Analyzer (IA) in order to calculate statistical parameters from the 2D images.

Basic 2D geometries were studies to understand the Aspect Ratio distribution results from the IA. In addition, a grain shape reconstruction was made from the 2D images.

It was found that every grain geometry has a unique projected length distribution function, and the area under the projected length distribution graph is equal to the grain perimeter.

Density probabilities of 3D shapes were extracted using unique Matlab Codes. It was found that some grain properties can be extracted from the probability density graphs like grain ratios and grain shape.

By using the BT different crosshead speeds, Failure properties such as Maximum Stress, Strain, and stiffness were calculated. It was found that (1) the modulus as a function of grain size can be described by a simple polynomial approximation; (2) the macro-elastic modulus as a function of crosshead speed (CHS) can be described by a simple power law; (3) The failure properties (Max Stress, Strain and fracture energy) were found to be better for grain size less than 300?m, and (4) The macro properties like modulus are not affected by the grain size, due to the pressing procedure which 'erases’ the differences.

In summary, (1) Regardless to Grain Ratio, a synergy affect
was found using the bi-modal material, and also (2) there was no correlation
between the grain size and the fracture toughness.^{ }