A calorimetric study of wildland fuels

The burning of two species of pine needles: Pinus halepensis and Pinus pinaster, was studied to characterize the behavior of the forest floor in wildland fires. These fuels are representative of the Mediterranean ecosystem and have very different shapes and surface-to-volume ratios. Calorimetry was performed using the FM-global fire propagation apparatus (FPA). To better understand the effects of transport in the fuel beds, the standard sample holder was replaced by a holder that allowed for the porous properties of the fuel to be studied in a systematic manner. These holders were designed with holes on the surface to allow for different air flow rates to pass through the holder and into the fuel sample. These characteristics created different internal fuel bed conditions and were the first such tests that could be identified that examined transport on this level in these types of wildland fuels. Tests were conducted under natural convection and forced flow. The test series results were analyzed with respect to the direct values of the measured variables and calculated values of heat release rate. Discrete variables of time to ignition, duration of flaming combustion and peak heat release rate were compared using an analysis of variance method. As the experiments were conducted under well-ventilated conditions, the heat release rate calculated by calorimetry was compared to mass loss rate and heat of combustion. CO concentration in time proved to be a good indicator of the combustion dynamics in the fuel bed. Heat release rate, time to ignition and time to reach peak heat release rate indicated a strong dependence on flow conditions and on fuel specie. It was shown that the transport processes in the fuel beds had a significant effect on the burning characteristics

Transformation kinetics of alloys under non-isothermal conditions

The overall solid-to-solid phase transformation kinetics under non-isothermal conditions has been modeled by means of a differential equation method. The method requires provisions for expressions of the fraction of the transformed phase in equilibrium condition and the relaxation time for transition as functions of temperature. The thermal history is an input to the model. We have used the method to calculate the time/temperature variation of the volume fraction of the favored phase in the alpha-to-beta transition in a zirconium alloy under heating and cooling, in agreement with experimental results. We also present a formulation that accounts for both additive and non-additive phase transformation processes. Moreover, a method based on the concept of path integral, which considers all the possible paths in thermal histories to reach the final state, is suggested.Comment: 16 pages, 7 figures. To appear in Modelling Simul. Mater. Sci. En

Uniaxial compressive strengths of rocks drilled at Gale crater, Mars

Measuring the physical properties of geological materials is important for understanding geologic history. Yet there has never been an instrument with the purpose of measuring mechanical properties of rocks sent to another planet. The Mars Science Laboratory (MSL) rover employs the Powder Acquisition Drill System (PADS), which provides direct mechanical interaction with Martian outcrops. While the objective of the drill system is not to make scientific measurements, the drill's performance is directly influenced by the mechanical properties of the rocks it drills into. We have developed a methodology that uses the drill to indicate the uniaxial compressive strengths of rocks through comparison with performance of an identically assembled drill system in terrestrial samples of comparable sedimentary class. During this investigation, we utilize engineering data collected on Mars to calculate the percussive energy needed to maintain a prescribed rate of penetration and correlate that to rock strength