This study investigated the influence of material properties on fatigue life through laboratory fatigue testing of eleven Superpave hot mix asphalt (HMA) mixtures in use at the Virginia Smart Road. Mixtures were sampled from the plant and produced in the laboratory to investigate the influence of production method. Specimens were cut from the in-situ pavement and compacted in the laboratory to evaluate the influence of compaction method. Third point beam fatigue testing was performed at 25ºC and 10Hz. Additional testing at frequencies of 1 Hz and 5Hz, and at 10 Hz including rest periods of 0.4sec and 0.9sec were performed for one mixture to explore the impact of frequency and rest periods. Analyses were performed on the strain-life relationships and predicted endurance strain limits for the mixtures. Investigation of strain-life relationships for several mixtures indicated that small differences in mixture volumetrics due to the production method have minimal impact on the laboratory fatigue performance of HMA. Comparisons of expected fatigue performance for one mixture indicated that shorter fatigue lives (under the same strain conditions) may be expected for laboratory-compacted specimens when compared to field-compacted specimens, despite visual observation of damage (surface cracking) in the field-compacted specimens. Testing performed on one mixture to determine the influence of different loading frequencies showed that fatigue life was independent of the requencies tested. Investigation of rest period inclusion indicated no differences in fatigue life for loading conducted at 10 Hz frequency and no rest period, 0.4sec rest period, or 0.9sec rest period. The evaluation of specimens cut from the in-situ pavement indicated that location within the lane and orientation did not significantly affect laboratory fatigue performance. The effect of aggregate size was considered; however, results were inconclusive. Using predictive strain-life fatigue equations, the benefits of polymer-modification of binders and use of SMA were shown for mixtures produced in the laboratory according to the job mix formula and to match the plant-produced volumetrics. Evaluation of the predicted fatigue strain endurance limit was performed using an energy-based and an empirical method. The energy method was shown to estimate significantly higher endurance limit strains for mixtures. / Ph. D.

Permeability of hot mix asphalt (HMA) is a property that is important to the pavement's durability. Measuring permeability along with density will give a better indication of a pavement's durability than density alone. The presence of water for extended periods of time in the pavement is directly linked to early deterioration. The first goal of this research is to study the anisotropic nature of hot mix asphalt permeability within the lab, which required the development of a horizontal permeameter. This method is inexpensive and suitable for a lab technician to use and analyze. A series of samples with different air void contents were used to observe how the ratio of vertical to horizontal permeability changes with air void content. The second goal was to develop a modified field permeameter to study the water-pavement contact area effect on field permeability. A reliable sealing system was created that is consistent and is not detrimental to the pavement surface. The results of the study show that larger contact areas yield increasing influence of vertical flow, which represents the one dimensional assumption of Darcy's Law falling head method. The third goal was to validate the results by simulating the field permeability test with a finite element model. A number of simulations with different permeability values and anisotropic permeability ratios were conducted. The horizontal and vertical flows were observed within the test area to analyze the flow pattern and influence of the directional permeability. The results matched the trends found in the field permeability study. / Master of Science

Call number: LD2668 .T4 1978 R52 / Master of Science

SAMMANFATTNING Bakgrund Arbetsplatser som bedriver hälso- och sjukvård är de verksamheter där flest arbetsskador och sjukdomar anmäls till följd av hot och våld. Sjuksköterskors arbetsmiljö påverkas av hot och våld då våldshandlingar sker i samband med det patientnära arbetet. Personcentrerad omvårdnad är en del av omvårdnaden som kan leda till vårdrelationer baserade på tillit och trygghet. Vårdrelationer kan skapa möjlighet för sjuksköterskor att få förståelse för patienters behov och resurser. Syfte Att beskriva hur hot och våld kan påverka sjuksköterskan i vårdrelationen med patienter inom hälso- och sjukvård. Metod Metoden som valdes var litteraturöversikt. Sökningar efter artiklar gjordes i databaserna PubMed, Medline och CINAHL. Resultatet baseras på 20 vetenskapliga artiklar som klassificerades, värderades och sammanställdes i en matris. Resultat Sjuksköterskor påverkades psykiskt och fysiskt av hot och våld. Konsekvenserna manifesterades genom att sjuksköterskor agerade utifrån ett undvikande beteende där försämrad kommunikation var ett återkommande problem. Strategier för att etablera och upprätthålla vårdrelationer med patienter visade sig vara sjuksköterskors förmåga att ge uttryck för lyhördhet och förståelse. Slutsats Kunskap kring hur vårdrelationen mellan sjuksköterskor och patienter kunde påverka förutsättningar för personcentrerad omvårdnad var nödvändig vid omvårdnad av hotfulla och våldsamma patienter. Otrygga arbetsplatser försämrade förutsättningarna för sjuksköterskor att erbjuda personcentrerad omvårdnad och vårdrelationer baserat på tillit och trygghet.

published_or_final_version / abstract / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

The retrogression-reaging (RRA) and hot forming behavior of AA7075 were studied. AA7075 is a high-strength alloy used in applications where weight is of particular importance, such as in automobiles. Like many of the high-strength aluminum alloys, AA7075 requires elevated temperature forming to achieve ductility comparable to steels at room temperature. Since AA7075 is a precipitation hardening alloy, heat treatments during forming and production need to be closely controlled to limit any loss of strength due to changes in the microstructure. Two new forming concepts are introduced to explore the feasibility of forming AA7075 in manners compatible with current automotive manufacturing processes. They are RRA forming and solution forming. These concepts seek to improve upon the room-temperature formability of AA7075-T6 and incorporate the paint-bake cycle (PBC) into the heat treatment process. The PBC is a mandatory heat treatment used to cure the paint applied to automobiles during production. Currently, the PBC is conducted at 180 °C for 30 minutes. RRA behavior was studied with molten salt bath treatments between 200 and 350 °C. The PBC was used in lieu of the standard 24 hour reaging treatment conducted at 121 °C. It was determined that retrogression treating below 250 °C was acceptable for RRA forming, with retrogressing at 200 °C producing the hardest material after reaging by the PBC. The formability of AA7075-T6 during RRA forming was evaluated by tensile testing at 200 and 225 °C. Ductility of AA7075-T6 at RRA forming temperatures was double compared to those produced at room temperature. RRA forming was demonstrated to achieve this improved ductility and a final material hardness after the PBC of only slightly less than the peak-aged condition. In addition, solution forming behavior was studied at 480 °C. Solution forming can increase ductility compared to RRA forming, but it requires aging at 121 °C prior to the PBC to produce peak-aged hardness. / text

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