An Ergonomic Evaluation of a Wrist Brace for Canadian Tree Planters

Tree planting is one of the most physically demanding occupations in Canada and as a result, tree planters are at an elevated risk of injury, specifically at the wrist. Wrist injuries develop on account of the highly repetitive nature of the job, as well as other musculoskeletal risk factors including non-neutral wrist postures and high impact forces sustained at the wrist during shovel-ground impact. As a result, wrist brace use has become common among planters, in an effort to limit deviated wrist postures while also providing enhanced stability at the wrist. The external stability provided by a wrist brace is thought to reduce the muscular effort required to provide stiffness at the wrist during shovel-ground impact. Since these prospective benefits have not been formally investigated, the purpose of this study was to determine the effect of a wrist brace on wrist posture, muscle activity, and joint rotational stiffness about the wrist joint (for two degrees of freedom: flexion/extension and ulnar/radial deviation). We hypothesized that the brace would promote more neutrally aligned wrist angles, and that muscle activity and joint rotational stiffness would also decrease when participants wore the brace. Fourteen tree planters with at least one season of experience were recruited to complete two planting conditions in a laboratory setting: one condition while wearing the brace (with brace, WB) and one condition without the brace (no brace, NB). The results from this study showed that at shovel-ground impact muscle activity trended towards increasing in three muscles when participants wore the brace. Additionally, wrist angles improved about the flexion/extension axis of rotation while increasing in deviation about the ulnar/radial axis of rotation when participants wore the brace. Joint rotational stiffness increased when participants wore the wrist brace. Participants from this study indicated difficulty gripping the shovel due to the bulk of the wrist brace, and this feature is discussed with possible suggestions for future iterations of design. In addition to grip diameter this analysis also prompts the suggestion that hand length and experience should also be considered in the design of tree planting tools, specifically an ergonomic aid such as a wrist brace.

THE MICROSTRUCTURES OF ZR-EXCEL ALLOY: EFFECTS OF HEAVY ION IRRADIATION, PLASTIC DEFORMATION, THERMAL TREATMENT AND IN-SITU HEATING

Zr-Excel alloy (Zr-3.5Sn-0.8Nb-0.8Mo) is a dual phase (α + β) alloy in the as-received pressure tube condition. It has been proposed to be the pressure tube candidate material for the Generation-IV CANDU-Supercritical Water Reactor (CANDU-SCWR). In this dissertation, the effects of heavy ion irradiation, deformation and heat treatment on the microstructures of the alloy were investigated to enable us to have a better understanding of the potential in-reactor performance of this alloy. In-situ heavy ion (1 MeV) irradiation was performed to study the nucleation and evolution of dislocation loops in both α- and β-Zr. Small and dense type dislocation loops form under irradiation between 80 and 450 °C. The number density tends to saturate at ~ 0.1 dpa. Compared with the α-Zr, the defect yield is much lower in β-Zr. The stabilities of the metastable phases (β-Zr and ω-Zr) and the thermal-dynamically equilibrium phase, fcc Zr(Mo, Nb)2, under irradiation were also studied at different temperatures. Chemi-STEM elemental mapping was carried out to study the elemental redistribution caused by irradiation. The stability of these phases and the elemental redistribution are strongly dependent on irradiation temperature. In-situ time-of-flight neutron diffraction tensile and compressive tests were carried out at different temperatures to monitor lattice strain evolutions of individual grain families during these tests. The β-Zr is the strengthening phase in this alloy in the as-received plate material. Load is transferred to the β-Zr after yielding of the α-Zr grains. The temperature dependence of static strain aging and the yielding sequence of the individual grain families were discussed. Strong tensile/compressive asymmetry was observed in the {0002} grain family at room temperature. The microstructures of the sample deformed at 400 °C and the samples only subjected to heat treatment at the same temperature were characterized with TEM. Concentration of β phase stabilizers in the β grain and the morphology of β grain have significant effect on the stability of β- and ω-Zr under thermal treatment. Applied stress/strain enhances the decomposition of isothermal ω phase but suppresses α precipitation inside the β grains at high temperature. An α → ω/ZrO phase transformation was observed in the thin foils of Zr-Excel alloy and pure Zr during in-situ heating at 700 °C in TEM.