Papers by Keyword: Bending

Abstract: Anisotropic conductive film (ACF) is frequently used in the packaging manufacture for fine-pitch conductivity and interconnection, maintaining the electrical and mechanical connections between micro-electrodes. A key determinant of good conductivity is the deformation, fatigue, and breakage of conductive particles within the ACF packaging. This study aims to measure the resistance changes of specific conductive channels and observe the microscopic fatigue damage of compressed ACF conductive particles through the fabrication of Flex Printed Circuits (FPC) / Indium Tin Oxide-coated Polycarbonate (ITO-coated PC) specimens and the setup of bending experiments. The results show that the deformation, fatigue, and breakage of conductive particles will quantitatively affect electrical conductivity performance. By microscopically observing the breakage morphology of conductive particles before and after bending, it can be found that bending in the ACF packaging area further exacerbates the previously compressed and broken conductive particles, with cracks continuing to grow and shatter.

Abstract: This study explored the capability of sheet forming of JIS ADC12 aluminum alloy, commonly used for die casting. Despite the poor ductility of ADC12, we attempted to improve this property by applying rapid solidification through an unequal diameter twin roll caster. A strip with a thickness of 3.7 mm was cast at a speed of 20 m/min. The as-cast strip was then cold rolled and annealed to investigate its sheet-formability by deep drawing, three-roll bending and V-bending. This research also investigated the elements of ADC12 that contribute to poor ductility, with a focus on the impact of Mg, Cu, Fe, and Zn during the deep drawing process.

Abstract: LVD Company NV and Kawasaki Heavy Industries, ltd. developed the cutting-edge, high performance CNC press brake [1] for high accuracy/precision bending of approx.10m (L) by 2.5m (W) size aircraft skins. Those skin sheets have complex shapes which include mainly machine milled thickness reduction area called pockets, thickness tapers, cutouts for the windows and doors. Due to those characters, the materials have large thickness variation between less than 2 mm and more than 11 mm in a single skin sheet. Here in this paper, the overview of this intelligence press brake equipment and its forming process are described. The materials with complex shapes described above can be bent accurately including material edges with the features of the press brake which are the synchronized material handling system, 210 numbers of variable punches, the special die suitable for the variable punches, the curvature measurement devices, and an automated bending mechanism with curvature feedback /feedforward. In addition, cardboard-like-filler jigs which are used to make thickness variations flat in a traditional bending process and shims to adjust regional press strokes can be eliminated, which reduce significant process time and product quality without worker’s superior skills. As a result, full automation of accurate bending process of aircraft skins have been achieved.

Abstract: In the current paper, composites with both thin and thick plies are designed to meet specific criteria and tested under both in plane and out of plan critical loading conditions. The tests adopted are bolted joint, drop-weight impact, compression after impact, Charpy impact, bending, and bending after thermal aging. The results of the proposed design are compared with that of the traditional composites and show higher improvement in most of the load cases by using thin plies inside the lamination process with the traditional ones. The results showed that the two proposed alternatives with thin plies are of higher advantage for the bolted joints problem. On the other hand, the alternative with thin plies distributes to be surrounding each traditional ply is of high advantages for both the impact and the bending problems. The alternative with a core of thin plies at the middle of the laminate is of high advantage for the compression after impact.

Abstract: Since the material properties of paperboard depend on the processing strain rate and the temperature elevation of the paperboard, the mechanical conditions of the scoring tool (creasing knife) are important for precisely and stably folding the scored zone of the paperboard. When the temperature and the indentation velocity of the creasing knife are changed irregularly during the scoring process, the permanent-indented (residually scored) depth of the paperboard seems to be affected by the temperature and the indentation time of the creasing knife. Although the temperature-dependent and time-dependent behavior of several thin paperboards have been known in the past, their combined behavior was not sufficiently discussed regarding the crease bending characteristics of the paperboard. In this work, the time-dependent and temperature-dependent scoring, and the corresponded bending characteristics of liquid-container-purpose paperboard of basis weight 313g/m² (thickness of t = 0.47mm) were experimentally investigated using a bending (folding) tester, when varying the holding time and the temperature of a flat-edge creasing knife at two levels of the normalized indentation depth d/t = 0.68 and 1.02. As the results, the first peak bending moment M_p1, the first stiffness C₁ (the gradient of bending moment resistance by the folding angle at an angle of 0—4 degrees), and the rating bending moment resistance at the right-angle M_90,1(0) were characterized with the holding time and the temperature elevation of the creasing knife at the pre-stage (scoring) process. Also, some explicit expressions of C₁, M_p1, M_90,1(0) with the permanent scored depth were revealed as a static relationship. It is concluded that the temperature variation and the holding time of the creasing knife are important parameters which must be controlled in the manufacturing process of liquid package.

Abstract: This paper reports on the mechanical properties in relation to the microstructure of the Mg-rich aluminium alloy joints fabricated through friction stir welding (FSW) and tungsten inert gas (TIG) welding techniques. The microstructure, tensile, and bending tests were conducted on friction stir, and TIG welded joints. Most coarse grains (27.81mm) dominated the joint produced using the TIG welding technique, while the refined grains (11.26 mm) mostly dominated the joint made through the FSW technique. The ultimate tensile strength (UTS) of the joint fabricated using the FSW technique was higher (379 MPa) compared to the TIG-welded joint (260 MPa). However, the inverse behaviour was observed when looking at the tensile elongation of the very same joints. The bending results correlated with UTS results, and this phenomenon was attributed to the microstructural grain size.

Abstract: Instability is one of the factors causing damage and injury that results in permanent disability. To increase the stable load-carrying capacity, a simplified and efficient computational method for determining the first critical load is necessary for the structure's structural design, application and safety. This study aims to determine the characteristics of the critical bending moment M_bcr and the critical torsion moment M_Tcr due to geometric size variations in the square, diamond, and circle cross-sectional hollow pipes so that consideration of the selection of hollow pipe size and cross-sectional shape is obtained under pure bending and pure torsion to minimize the occurrence of instability of the structure. The geometric size variation is carried out by changing the value of a/t in the quadrilateral pipe, the value of D/t in the circular pipe, and the length of the pipe L in each cross-sectional shape. This research was conducted using Finite Element Analysis-based software with linear and nonlinear buckling analyses. The moment load is given at the centre point of the model end, and the boundary conditions are set to see the deformation on the mid-span section of the pipe. The results showed that M_bcr and M_Tcr were inversely proportional to the values of a/t, D/t, and . The largest value of M_bcr belongs to the circular pipe. The value of M_bcr in the diamond pipe is greater than the square pipe but getting closer to the same as the value of L increases the M_Tcr value of both cross-sections is the same. The M_Tcr curve in the cross-section of the circle has a higher degree of steepness than the square and diamond cross-section. At the same value, the more the value of a/t and D/t increases thickness change has more compared to the circular pipe. At the same L, the greater the value of a/t and D/t, the difference in the M_bcr between the cross-section of the circle and the quadrilateral is smaller, but the difference in M_Tcr tends to be the same. At the same value of a/t and D/t, the oval deformation value and angle of twist will get bigger, but the M_bcr and M_Tcr values are getting smaller and will be constant at a given pipe length.

Abstract: This paper considers the softening and flattening treatment of Schizostachyum Lumampao Bamboo as part of a process in its preparation for utilization. Bamboo half-culm samples with thicknesses of either 5.00 mm or 6.00 mm was soaked in palm oil at either of two temperatures (100°C or 160°C) with an application of 50 N load to simulate the flattening process for a period of either 2700 sec. (45 mins.) or 3600 sec. (60 mins.). By measuring the height of the bamboo half-culm before and after the thermal treatment, a relationship was derived between the total heat transferred into the bamboo culms and the flattening behavior. Furthermore, after the flattening, the bending strength of the culms exhibited an exponentially decaying trend and the fracture strength a bi-modal behavior which is confirmed by other studies. This study reports a derived parameter designated as the thermodynamic bending stiffness of about 4 MPa for the flattening process.

Abstract: Multilayer sheets or films have many potential applications in micro-nanoelectromechanical systems. When surface and scale effects are not considered, the bending of multilayer film systems can theoretically be discussed by the classical Stoney formula or Timoshenko formula. When the system has anisotropic surface stress or mismatch strain, the four-parameter bending model proposed by Narsu et al. can be used. However, if the thickness of the film is several nanometers and the bending radius of curvature is less than 1micron, the existing theoretical model is no longer applicable. For this reason, a bending formulation for the nanomulti-layer film system is derived and the structure of the multilayer film is optimized in this paper.

Abstract: This paper introduces a generalized viscoplastic model and describes its application in treating the longitudinal fracture of inhomogeneous beam structures. The model is a combination of an arbitrary number of parallel units. Each unit is obtained by two springs and a dashpot. Besides, a frictional slider is placed parallel with one of the springs in each unit of the model in order to treat the plastic strains. The time-dependent constitutive law of the model obtained by considering strains, stresses and equilibrium of the model components is used in deriving solution of the strain energy release rate for the longitudinal crack in the viscoplastic beam.