Browsing by Author "Smith, Frederick W., advisor"
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Item Open Access Effect of interpass temperature on the structure and properties of multipass weldments in high performance nickel alloys(Colorado State University. Libraries, 2011) Petro, John S., author; Smith, Frederick W., advisor; Sampath, Walajabad S., committee member; James, Susan P., committee member; DuChateau, Paul C., committee member; Klarstrom, Dwaine, committee memberNickel alloys comprise an important group of engineering materials which are used primarily for their exceptional resistance to corrosion and their ability to maintain good mechanical strength over a wide temperature range, (both low and high) in demanding industrial applications. Welding is a primary fabrication process for these alloys. It has been a generally accepted practice to maintain a maximum interpass temperature of 200°F or lower when multipass welding many nickel alloys to prevent defects such as cracking or loss of corrosion resistance. This practice has been based on recommendations by many of the nickel alloy producers. A low maximum interpass temperature can increase the welding time which increases fabrication costs. According to the author's industry contacts and based upon the author's industrial experience as well as the author's examination of the literature, there has been little or no systematic research on the effect of interpass temperature for multipass welding of nickel alloys. In fact, the same is true for the establishment of the basic robotic welding parameters using the new generation of digital power supplies for these alloys. This dissertation presents research on the effect of interpass temperature on two nickel alloys; HASTELLOY® C-2000® and HASTELLOY® B-3®. Welding parameters were also developed for these alloys and also for HAYNES® 230® alloy using Gas Metal Arc Welding, GMAW, as a single process for both the root and fill weld passes. Weldments were made at 5 different interpass temperatures, 100°F - 500°F, in 100°F increments, for these alloys in thicknesses of 0.25 inch and 0.5 inch. Transverse weld specimens were then tested according to AWS B4.0:2007 using tensile, bend, and hardness tests. Transverse weld specimens were corrosion tested according to ASTM G28A for the HASTELLOY C-2000 alloy and the HASTELLOY B-3 alloy was subjected to 20% HCl at 149°C for 96 hours in an autoclave. The specimens were also examined using optical light microscopy for intergranular corrosion attack, weld fusion, cracking, and heat affected zone (HAZ) microstructure effects. (HASTELLOY, HAYNES, C-2000, B-3, and 230 are registered trademarks of Haynes International, Inc.) No significant loss of tensile strength was found at any of the higher interpass temperatures. All ultimate tensile strengths for both alloys were above the ASME Boiler and Pressure Vessel Code Section IX minimum. All samples passed 2T transverse face bend tests. Some lack of fusion was observed at the root of some samples at random interpass temperatures. No noticeable change in the HAZ microstructure or cracking was observed at the highest interpass temperature for both the HASTELLOY C-2000 and the HASTELLOY B-3 alloys. No significant corrosion attack was found along the weld, face or root sides, for both alloys at the higher interpass temperature of 500°F. It was concluded that a higher interpass temperature could be specified for these alloys without any appreciable loss of strength, weld soundness, loss of corrosion resistance, or detrimental effect to microstructure. It was also shown that the GMAW process could be used as a sole welding process but more development is needed to decrease process variability in the root pass and to develop a complete welding procedure specification.Item Open Access Effects of mountain pine beetle on forest structure and fuel load 25-30 years after an outbreak in western Colorado(Colorado State University. Libraries, 2011) Pelz, Kristen A., author; Smith, Frederick W., advisor; Jacobi, William R., committee member; Martin, Patrick H., committee memberMortality of lodgepole pine (Pinus contorta (Dougl. Ex. Loud.) caused by mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) has caused concern about long-term forest structure and wildfire hazard changes. In 2010, I identified and sampled areas affected by a 1980s MPB outbreak to quantify forest changes in the 25-30 years following mortality. Stands in Eagle County, Colorado with >30% 1980s lodgepole pine mortality were identified using USDA Forest Service aerial survey maps and inventory data. Stands fell into two forest type groups: lodgepole pine and mixed conifer. I sampled 20 stands to measure forest species and size structure and down woody fuel accumulations. I compared 1980s inventory data to 2010 data to find differences between forest type groups in their post-outbreak changes. Lodgepole pine stands recovered to pre-outbreak overstory total basal area, density, and species composition by 2010, while in mixed conifer stands basal area and density were significantly less in 2010 than before the outbreak. In mixed conifer stands, lodgepole pine overstory basal area was reduced from 66% of total in the 1980s to 51% in 2010.Understory tree density increased roughly six-fold in both forest types between the 1980s and 2010. The overall increase in understory density was due to a ten-fold increase in seedling/sapling (trees 0.6 m tall to 3.8 cm dbh) numbers. In lodgepole pine stands, the most abundant species in the 1980s understory was subalpine fir, followed by lodgepole pine. By 2010, lodgepole pine and subalpine fir were the majority of larger understory trees; aspen and subalpine fir were most abundant among smaller understory trees. In mixed conifer stands, subalpine fir and Engelmann spruce consistently dominated all understory size classes in the 1980s and 2010. Total down woody fuel load averaged 71 Mg ha-1 and did not differ between forest type groups. Overall, my results suggest that long-term forest recovery trajectories are dependent on pre-outbreak species composition, though understory densities are likely to increase regardless of non-host species abundances. These shifts in species and size composition by 25-30 years after outbreak likely have substantial impacts on forest health, potential fire behavior and ecosystem processes. We speculate that forest recovery following the current MPB outbreak will be similar to observed changes following the 1980s outbreak in these areas.Item Open Access Forest regeneration and future stand trajectories following mountain pine beetle-caused lodgepole pine mortality(Colorado State University. Libraries, 2014) Pelz, Kristen A., author; Smith, Frederick W., advisor; Dickinson, Yvette L., committee member; Martin, Patrick H., committee member; Rhoades, Charles C., committee memberA mountain pine beetle (MPB) (Dendroctonus ponderosae) outbreak that began in the late 1990s has killed lodgepole pine (Pinus contorta var. latifolia) on up to 10 million hectares in western North America. Over one million hectares have been affected in northern Colorado and southern Wyoming. The large footprint of this disturbance has prompted widespread concern about the composition, structure, and function of forests as they develop following MPB. In this dissertation, I ask how variation in species composition and mortality level will affect the future forest in the Southern Rockies. I used forest growth models to predict forest structure and fuel loads during the century after MPB outbreak. I compared three lodgepole pine-dominated forest types (all > 80 % lodgepole by basal area) and the simulated effects of no-action and fuel reduction treatments. Forest with Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa var. lasiocarpa) became much more dominated by these species, resulting in highly hazardous canopy fuels. In contrast, stands of lodgepole and aspen (Populus tremuloides) did not shift composition and did not show a marked increase in fire hazard. The effects of management were also differed: hazardous fuels were best mitigated in the forest types with spruce and fir, but treatment had few positive effects in the stands of only lodgepole and aspen due to their lower hazard without treatment. The results show management of lodgepole-dominated forests must consider even subtle variation in composition to be effective. I also examined post-outbreak regeneration in these forests. In mixed lodgepole pine and aspen stands, I asked if regeneration is sufficient to reforest areas affected by MPB. Both species excel in high light environments that are created by overstory mortality, but lodgepole pine is thought to require ground disturbance to regenerate. Aspen regeneration can be prevented by browsing. I found lodgepole regeneration is occurring in 85% of stands, and all stands had aspen sucker density above 1000 stems ha-1. Many suckers are damaged by browsing, but my results suggest that sufficient quantities of down lodgepole pine may protect suckers and allow them to recruit to the overstory. Overall, I conclude aspen and lodgepole forests are regenerating successfully and that these areas will remain mixed forests of both species in the future. Finally, I measured the effects of mortality level on regeneration. I compared regeneration density and growth of lodgepole, spruce, and fir in high (85% of basal area) and moderate (40% of basal area) mortality forest. Lodgepole pine regeneration density and growth was high where outbreak was most severe, though all species grew faster in high mortality than moderate mortality. All three species will likely be important to future forest in areas with high mortality, and lodgepole pine will play a substantial role. In contrast, in moderate mortality areas lodgepole pine regeneration is nearly absent and spruce and fir are growing fastest. Here the forest understory will be made up of shade tolerant species, and the forest will become progressively more dominated by these species as this stratum develops.Item Open Access Long-term forest recovery processes following a large, mixed severity fire in ponderosa pine ecosystems of the Black Hills, South Dakota, USA(Colorado State University. Libraries, 2011) Wudtke, Benjamin J., author; Smith, Frederick W., advisor; Battaglia, Mike A., committee member; Vaske, Jerry J., committee memberUnderstanding the pattern and timing of ecological recovery following wildfires in western forests has become critical as the area burned has dramatically increased in the past decade. This is especially important in ponderosa pine forests, where mixed severity fires lead to a complicated landscape mosaic of initial fire effects and patterns of recovery. I compared forest structural change in relation to initial fire severity, 10-years following the Jasper Fire of 2000 in ponderosa pine forests of the Black Hills of South Dakota. The Jasper Fire burned ~34,000 ha as a mixed severity fire with 25% low, 48% moderate and 27% high severity. I measured 43 sites within and adjacent to the Jasper fire perimeter which represented unburned areas and areas burned at low, moderate and high severity. These sites were established in 2001, immediately following the Jasper fire, and were measured annually for the first 5 years. My work constitutes the 10-year re-measurement of these sites. I assessed forest recovery as accumulation of forest floor biomass, seedling regeneration, snag dynamics, tree survivorship and growth of surviving trees. Stand density has remained constant for unburned sites at ~25 m2 ha-1 since the fire, but has continued to decline in low and moderate sites which were at 18 and 9 m2 ha-1. After 10 years, high severity sites had 63 Mg ha-1 of forest floor woody debris and were significantly greater than other burned sites and unburned sites where biomass was ~14 Mg ha-1. Approximately 80% of forest floor biomass on high severity sites was coarse woody material (>7.6 cm). There was no difference in fine material (<2.5 cm) between burned and unburned sites. The difference in coarse woody debris was due to the near complete fall of snags on high severity sites where 87% of fire-killed trees have now fallen. Litter on low severity sites was similar to unburned sites but is still significantly lower on moderate and high severity sites. Duff remains ~85 to 99% less on burned sites compared to unburned sites. Regeneration was substantial on unburned, low, and moderate severity sites. Unburned sites averaged ~6,000 seedlings ha-1, while low and moderate severity sites averaged ~1,200 seedlings ha-1. Regeneration was sparse on high severity sites and averaged 28 seedlings ha-1, likely attributed to factors limiting seed availability. Regeneration in the first 4-5 years was low on burned sites, when the Palmer Drought Severity index averaged. Since 2007, the amount of surviving seedlings substantially increased, when the drought index averaged 3.5. Tree growth measured as basal area increment for the 50 largest diameter trees per severity was significantly reduced on sites for 2001 through 2006 compared to five-year pre-fire growth. The only significant difference between severities during that time was in 2002 when moderate severity sites had higher relative growth. Growth for all sites increased in 2007 through 2010 and tree growth on moderate severity sites was significantly greater than unburned and low severity. The persistent drought from 2001 - 2006 had a more pronounced effect on tree growth than any fire effects. Forest recovery following mixed severity wildfire is strongly influenced by initial fire effects and postfire climate. Low severity areas are similar to unburned areas in nearly all aspects of stand structure. Overstory density was substantially reduced in moderate severity areas but had increased tree growth and seedling regeneration produced a new cohort of trees that will likely lead to the development of a multi-aged forest. Regeneration in high severity areas continued to be slow, and the persistence of a sparsely treed woodland forest, or cover type conversion in some instances, is likely. Importantly, many processes of recovery have accelerated in the past 3 years, as the persistent severe drought conditions of 2001 - 2007 have subsided.Item Open Access Maintaining fuel treatments with prescribed fire in ponderosa pine forests of the Black Hills, South Dakota(Colorado State University. Libraries, 2007) Battaglia, Michael A., author; Smith, Frederick W., advisor; Shepperd, Wayne D., advisorRecent wildfires in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests have increased efforts to create forest structures that reduce the risk of crown fire. In the Black Hills, these fuel-reduction treatments often result in a new cohort of ponderosa pine regeneration. If no action is taken, the efficacy of these fuel treatments eventually diminishes as the regeneration grows and creates a ladder fuel complex. In this dissertation, I examine the utility of using prescribed fire to control this regeneration. I also explore if restoration of historical forest structure would result in reduced crown fire risk.