Macroscopic and Microscopic Residual Stresses in Ceramics Due to Contact Loading
The paper deals with microplastic deformation and macroscopic residual stresses in silicon nitride ceramics due to contact loading and their effect on the near-surface strength. Depth-resolving X-ray residual stress measurements on shot peened samples detect high microplastic deformation and macroscopic compressive residual stresses up to 1.3 GPa at the surface decreasing to zero within 10 pm. These high compressive stresses enhance the load bearing capacity in the ball-on plate test up to 50 % compared to polished samples.
Strength Properties of Surface-Machined Components of Structural Ceramics
The high quality required for special components of structural ceramics can only be achieved by an additional fine-machining. Since processes like lapping or grinding strongly influence the service behaviour of the components and in addition cause a considerable part of the manufacturing costs there is a need for parameter studies in order to optimize the resulting quality and reduce the costs of the machining process. Therefore, the strength-controlling surface effects have been investigated using a newly developed method for the determination of micro-strains and residual stresses by x-ray diffraction techniques. The resulting information on the defect situation in the surface layer can be modeled by assuming hypothetical cracks. When the additional information on the distribution of the residual stresses caused by machining and the strength properties obtained from bending tests are taken, as a consequence, the effects of damage processes and residual stresses on the strength of ceramics can be quantified by the methods of fracture mechanics. Typical case studies will be discussed in which different grinding and lapping procedures are applied to specimens of silicon nitride and alumina.
PRECISION FARMING APPROACHES TO SMALL-FARM AGRICULTRUE
Precision farming implies a management strategy to increase productivity and economic returns with a reduced impact on the environment. It is based on the application of information technology to a description of variability in the field, variable-rate operations and the decisionmaking system. There are three technology levels and three strategies in the development of precision farming. Precision farming practices can be used on small farms as well as big ones, and they play a core role in rural development programs which are integrated with industry. A real-time soil spectrophotometer was developed to describe soil variability in farmers' fields, to be used in precision farming.