Study on the Mechanical Properties of Stay Cable HDPE Sheathing Fatigue in Dynamic Bridge Environments
As the main force-bearing component of a cable-stayed bridge, a durable stay cable is paramount to the safety and durability of the entire bridge. High-density polyethylene (HDPE) sheathing is the main protective component of a stay cable and is the key to insuring cable durability. To address the issue of HDPE sheathing fracture on service, strain level data for in-service, HDPE bridge cable sheathing was used in this study as the basis for HDPE material aging and fatigue testing. A fatigue yield phenomenon with a yield platform on the hysteresis curve of the fatigue cycles is observed by the fatigue test. The parameters to describe this phenomenon are proposed and defined in this paper. A preliminary examination of the relationship between these parameters and the factors, such as the number of cycles, the strain amplitude, and strain rate, are presented. Based on the results obtained, it is suggested that the condition of fatigue yield of HDPE sheathing be defined as the fatigue durability limit state for the purposes of durability design, assessment, and protection of cable-stayed bridges.
Machining Optimization of HDPE Pipe Using the Taguchi Method and Grey Relational Analysis
Abstract The demand for the machining and cutting of plastic parts is in continuous increase. The present study is intended to investigate the optimization of high density polyethylene (HDPE-100) orthogonal turning operation using the Grey Relational Analysis (GRA). Accordingly, experimental tests based on Taguchi method are performed to establish a correlation between cutting parameters on one hand and machining force, specific cutting force and roughness of machined surface on the other hand. An optimal parameters combination for the turning process is obtained. In addition to regression models deduction, the analysis of variance (ANOVA) is applied to identify the most significant factors. It is found that the order of the importance of controllable factors to the tangential cutting force (Ft) is feed rate (f), depth of cut (ap) and cutting speed (Vc). However, when considering the importance with respect to specific cutting force (Ks), the order becomes (Vc), (ap) and (f). Finally, the order of cutting parameters according to mean roughness criteria, represented by (Ra), (Rz) and (Rt), shifts to (f), (Vc) and (ap). The optimized cutting regime ensuring minimization of roughness and cutting forces is well described by Vc = 188 m/min, f = 0.14 mm/rev and ap = 3 mm. This study unveiled new approaches based on combined GRA and ANOVA for machining other polymers such as tough reinforced polymers and composites used as human prosthesis.
Using Activity Theory in Developing Instructial Tools for Project Management Studies
Competence and skills of the project manager are significant to project success. The skills needed in project managersâ work cannot be learned only by reading the books or a lecture hall; one learns them by practice. Therefore, an important challenge for educational institutions is to develop pedagogical practices that allow students to participate in working life projects and to confront real-life problems. Project-based learning (PBL) offers a model that enables students to practice the skills and competences needed in working life projects by utilizing real-world work assignments in time-limited projects. Using PBL method alone does not necessarily guarantee learning result. In order to be successful, PBL method requires effective and competent supervision and guidance of students as well as appropriate tools for instruction. In this study the concepts from activity theory (AT) are applied to development tools for supervising project-based learning.