A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Agricultural Engineering, School of Environment, Resources and Development

Thesis (Ph.D.) - Asian Institute of Technology, 2006

The soil-tool adhesion creates an undue liability on power source to exert extra effort, at the cost of increased fuel consumption. Out of the various means of reducing soil-tool adhesion, biomimetic surface design modifications have recently exhibited an attractive bio inspired solution. Learning the tribological characteristics of soil-burrowing animals and copying their surface morphology on to tillage machinery with anti-adhesion objectives is the core theme of this research. With dung beetles as the role model, ultra high molecular weight polyethylene (UHMW-PE) was coupled to the concept of Mounting embossed array of protuberances on plough mouldboard - thus creating a hydrophobic (low surface-energy) non-smooth bionic tool surface. In an attempt to investigate suitable geometry of such construction units, this research comprised five shapes (flat, semi-spherical, semi-oblate, semi short-prolate and semi long-prolate) - resulting from the combination of dimensional factors (base diameter and protrusion height). To incorporate both shape and size, a dimensionless ratio of height to diameter (HDR) was introduced and used to characterize the effect of construction unit's physique. Experiments were conducted to evaluate the- influence of various geometrical shapes and sizes of such UI-IN'IW-PE protuberances (base diameter: 20-50 mm: protrusion height: 0-50 nun) on their relative effectiveness of lowering ploughing resistance of mouldboard plough in Bangkok clay soil at dry (21.8% d.b.), sticky (37.2% d.b.), wet (49.1% d.b.) and flooded (64.3% d.b.) soil-moisture conditions and 1, 3 and 5 km h"i three forward speeds. Percent reduction in ploughing resistance of bionic mouldboard plough in prevailing soil conditions with I-IDR = 0: 1-6% (dry), 16-22% (sticky), 14-20% (wet), 8-12% (flooded); with HDR = 0.25: 2-7% (dry), 18-36% (sticky), 17-33% (wet), 15-28% (flooded); and with HDR = 0.5: 10-16% (sticky), 617% (wet) and 12-26% (flooded). Whereas, HDR>0.5 increased the ploughing resistance by 7-29%. In addition, circular bionic plates were tested in dry (19.8% d.b.), sticky (36.9% d.b.) and flooded (60.1% d.b.) soil conditions for sliding resistance and normal adhesion. Soil at sticky limit exhibited the highest sliding resistance (77.8 N) and normal adhesion (3-7 kPa), whereas these values were 61.7 N and <0.2 kPa in dry, and 53.7 N and 0.5-1.5 kPa in flooded soil condition. Protuberances with HDR <- 0.5 lowered sliding resistance by 10-30% and the same reduced normal adhesion by 1060%. This research, in general, revealed the UHMW-PE protuberances with HDR <_ 0.5 were effective in lowering soil-tool adhesion. Protuberances with HDR > 0.5, on the other hand, were not found suitable for macro-morphological surface modification for bionic tools