Mechanical model of hollow-external-screw drill rod for lunar soil particle vertical conveying
This paper presents a mechanical model of drilling rod in lunar soil deep drilling process by expanding the theory of vertical screw conveyor. Space systems on lunar surface need to adapt to extremely bad environment and a drilling system would represent the fittest tool to collect soil sample to be analyzed in lunar exploration. Hollow-external-screw drill rod is a kind of most commonly used and reliable drill rod configuration which is one of the core executive components of lunar drilling- sampling mechanism. Drilling cuttings at the bottom of the hole are continuously sent to the lunar surface and the interaction between the drilling rod and the soil is difficult to model by numerical tools. Solid vertical transport theory in vertical screw conveyor and a soil-transporting mechanical model of long earth boring auger are applied to model the aforementioned interaction. In this force analysis of the mechanical model, not only the spiral angle variation is considered, but also the radial distribution and soil pressure in the particle vertical conveying. All these make the theoretical analysis more comprehensive than traditional methods. This paper also provides mathematical simulation of the soil-transporting process and the validation of the theoretical model mentioned above will be confirmed by the numerical and physical experiments.
Flame-Retardant Mechanism of EVA Modified with Expandable Graphite and Ammonium Polyphosphate
Ammonium polyphosphate(APP) and expandable graphite(EG) have been used to improve flame retardancy of poly(ethylene-co-vinyl acetate)(EVA).The flame-retardant mechanism of EVA/APP/EG system has been investigated by TGA,SEM,FTIR and XPS.SEM is used to observe the structures of the intumescent charred layers.EG expands into a worm-like char structure when exposed to heat,and this kind of char structure can block the mass and heat transfer,and protect the underlying EVA from combustion.The chars generated at different temperatures have been studied by FT-IR and XPS,respectively.The residues contain ammonium salt,unsaturated compounds,polyaromatics,phosphoric and ployphosphoric acids,and some EVA that is not burned completely.Based upon all the results mentioned above,a possible flame-retardant mechanism has been proposed.
Timber, its nature and behaviour
Preface. Acknowledgements. Chapter 1 - Structure of Timber. Chapter 2 - Appearance of Timber in Relation to its Structure. Chapter 3 - Mass Volume Relationships. Chapter 4 - Movement in Timber. Chapter 5 - Flow in Timber. Chapter 6 - Deformation Under Load. Chapter 7 - Strength and Failure in Timber. Chapter 8 - Durability of Timber. Chapter 9 - Processing of Timber. Index.