Designing an injection molded plastic part requires optimizing the part with respect to various stakeholders’ needs throughout its life cycle. The conditions in which a product is operating in service are often inadequately understood or specified, resulting in wrong material selection, which in turn leads to failure when the product is used. Many aspects interrelate with the initial part design and the essential rules of each should be taken into account to ensure a well-functioning plastic product. Regardless, a part design often passes sequentially from concept development to the manufacturing phase with features that unnecessarily complicate production, add costs and weaken the intended embodiment of the product. Therefore, a checklist was developed to ensure that oversights do not happen and verify that a design fulfills the requirements set for it. The commissioning company in the project was the design office Sytyte Oy. The aim of this thesis work was to investigate the effects of design decisions on the product’s feasibility and performance in service. The study focused on the underlying reasons for failures in plastic products, failure phenomena and ways of preventing them. The project started with literature research. To support the theoretical review, a small-scale survey was conducted among operators in plastic industry in Finland to strengthen the outcome of the project. The findings from the research were compiled into a checklist. The approach into the list was adopted from the FMEA method aiming to create a stripped-down version of it. The result offers a tool for anticipating and spotting possible failures by bringing up the influences that most frequently affect the part performance. It contributes to preventing delays in processing and premature failures in service. The checklist was verified by specialist consultation to receive suggestions and requirements for improvements and to ensure its reliability.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references. / vii, 49 leaves, bound ill. 29 cm

<p> A research programme is presented for assessing the capability of Hollow Structural Sections in Plastic Design. This investigation attempts to relate the flange slenderness and yield stress to the rotation capacity of Hollow Structural Sections subjected to both constant moment regions and to moment gradients. </p> <p> An experimental programme was performed on 31 different cross sections to evaluate the moment-curvature relationship which is of fundamental importance in Plastic Methods. The occurrence of local buckling for some sections in the compression flange and the consequent reduction in moment resistance is the critical factor which separates members into compact and non compact categories. </p> <p> The moment-curvature relations from tests are compared with analytical predictions. The plastic hinge rotations delivered by the present test sections are compared with the maximum practical requirements for plastically designed continuous beams. Theoretical elastic and inelastic buckling solutions of plate elements are also presented to relate to possible local buckling of the flats of square and rectangular hollow structural sections. </p> <p> Plate ratios of compression flanges are then selected for use in plastic design of hollow structural sections. Such a separation permits segregation into compact and non compact categories and can be used in working stress or elastic design methods. </p> / Thesis / Master of Engineering (ME)

The aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections (RHS) for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A large number of finite element analyses was also carried out on models of RHS beams. The conclusion is that cold- formed RHS can be used in plastic design, but stricter element slenderness (b/t) limits and consideration of the connections, are required. Further research, particularly into the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised. Bending tests were performed on cold-formed RHS to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design. The major conclusions of the beam tests were: (i) Some sections which are classified as Compact or Class 1 by current steel design specifications do not maintain plastic rotations considered sufficient for plastic design. (ii) The current design philosophy, in which flange and web slenderness limits are independent, is inappropriate. An interaction formula is required, and simple formulations are proposed for RHS. Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints, and welded and bolted internal sleeve knee joints, for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated. The most important finding of the joint tests was the unexpected fracture of the cold-formed welded connections under opening moment before significant plastic rotations occurred. The use of an internal sleeve moved the plastic hinge in the connection away from the connection centre- line thus eliminating the need for the weld between the RHS, or the RHS and the stiffening plate, to carry the majority of the load. The internal sleeve connections were capable of sustaining the plastic moment for large rotations considered suitable for plastic design. Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and horizontal wind loads. Two grades of steel were used for comparison. The aims of the tests were to examine if a plastic collapse mechanism could form in a cold-formed RHS frame, and to investigate if plastic design was suitable for such frames. In each frame, two regions of highly concentrated curvature were observed before the onset of local buckling, which indicated the formation of plastic hinges and a plastic collapse mechanism. An advanced plastic zone structural analysis which accounted for second order effects, material non-linearity and member imperfections slightly overestimated the strength of the frames. The analysis slightly underestimated the deflections, and hence the magnitude of the second order effects. A second order plastic zone analysis, which did not account for the effects of structural imperfections, provided the best estimates of the strengths of the frames, but also underestimated the deflections. While cold-formed RHS did not satisfy the material ductility requirements specified for plastic design in some current steel design standards, plastic hinges and plastic collapse mechanisms formed. This suggests that the restriction on plastic design for cold-formed RHS based on insufficient material ductility is unnecessary, provided that the connections are suitable for plastic hinge formation, if required. A large number of finite element analyses were performed to simulate the bending tests summarised above, and to examine various parameters not studied in the experimental investigation. To simulate the experimental rotation capacity of the RHS beams, a sinusoidally varying longitudinal local imperfection was prescribed. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity depended on both the web slenderness and flange slenderness, and that for a given section aspect ratio, the relationship between web slenderness and rotation capacity was non-linear. The main finding of the finite element study was that the size of the imperfections had an unexpectedly large influence on the rotation capacity. Larger imperfections were required in the more slender sections to simulate the experimental results. There should be further investigation into the effect of varying material properties on rotation capacity.

The aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections (RHS) for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A large number of finite element analyses was also carried out on models of RHS beams. The conclusion is that cold- formed RHS can be used in plastic design, but stricter element slenderness (b/t) limits and consideration of the connections, are required. Further research, particularly into the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised. Bending tests were performed on cold-formed RHS to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design. The major conclusions of the beam tests were: (i) Some sections which are classified as Compact or Class 1 by current steel design specifications do not maintain plastic rotations considered sufficient for plastic design. (ii) The current design philosophy, in which flange and web slenderness limits are independent, is inappropriate. An interaction formula is required, and simple formulations are proposed for RHS. Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints, and welded and bolted internal sleeve knee joints, for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated. The most important finding of the joint tests was the unexpected fracture of the cold-formed welded connections under opening moment before significant plastic rotations occurred. The use of an internal sleeve moved the plastic hinge in the connection away from the connection centre- line thus eliminating the need for the weld between the RHS, or the RHS and the stiffening plate, to carry the majority of the load. The internal sleeve connections were capable of sustaining the plastic moment for large rotations considered suitable for plastic design. Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and horizontal wind loads. Two grades of steel were used for comparison. The aims of the tests were to examine if a plastic collapse mechanism could form in a cold-formed RHS frame, and to investigate if plastic design was suitable for such frames. In each frame, two regions of highly concentrated curvature were observed before the onset of local buckling, which indicated the formation of plastic hinges and a plastic collapse mechanism. An advanced plastic zone structural analysis which accounted for second order effects, material non-linearity and member imperfections slightly overestimated the strength of the frames. The analysis slightly underestimated the deflections, and hence the magnitude of the second order effects. A second order plastic zone analysis, which did not account for the effects of structural imperfections, provided the best estimates of the strengths of the frames, but also underestimated the deflections. While cold-formed RHS did not satisfy the material ductility requirements specified for plastic design in some current steel design standards, plastic hinges and plastic collapse mechanisms formed. This suggests that the restriction on plastic design for cold-formed RHS based on insufficient material ductility is unnecessary, provided that the connections are suitable for plastic hinge formation, if required. A large number of finite element analyses were performed to simulate the bending tests summarised above, and to examine various parameters not studied in the experimental investigation. To simulate the experimental rotation capacity of the RHS beams, a sinusoidally varying longitudinal local imperfection was prescribed. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity depended on both the web slenderness and flange slenderness, and that for a given section aspect ratio, the relationship between web slenderness and rotation capacity was non-linear. The main finding of the finite element study was that the size of the imperfections had an unexpectedly large influence on the rotation capacity. Larger imperfections were required in the more slender sections to simulate the experimental results. There should be further investigation into the effect of varying material properties on rotation capacity.