Showing papers on "Deflection (engineering) published in 2018"

Determination of the effect of scan strategy on residual stress in laser powder bed fusion additive manufacturing

Abstract: Any literature investigation of Laser Powder Bed Fusion (L-PBF) manufacturing of metal parts would reveal that the development of internal stresses is a serious limitation in the application of this technology Researchers have used a variety of different methods to quantify this stress and investigate scanning strategies aimed at reducing or distributing this stress more evenly in the part The most common methods used to assess the levels of stress in parts are deflection based These techniques provide a rapid method to give a quantitative comparison of scan strategies and parameters Although studies have calculated the levels of stress relieved by the measured deflection, these studies often neglect the stresses that remain in the part after release This study shows that these stresses can still be considerable Non-destructive diffraction based methods can be used to calculate the profile of stress in a part but these are often prohibitively expensive or difficult to use on a large scale This study presents a methodology which combines deflection based methods with either the hole drilling or contour methods Results show that these experiments can be completed in a cost effective manner, with standard lab based equipment to generate a through thickness measurement of residual stress

Deflection of light by rotating regular black holes using the Gauss-Bonnet theorem

Abstract: In this paper, we study the weak gravitational lensing in the spacetime of rotating regular black hole geometries such as Ayon-Beato-Garc\'{\i}a (ABG), Bardeen, and Hayward black holes. We calculate the deflection angle of light using the Gauss-Bonnet theorem (GBT) and show that the deflection of light can be viewed as a partially topological effect in which the deflection angle can be calculated by considering a domain outside of the light ray applied to the black hole optical geometries. Then, we demonstrate also the deflection angle via the geodesics formalism for these black holes to verify our results and explore the differences with the Kerr solution. These black holes have, in addition to the total mass and rotation parameter, different parameters of electric charge, magnetic charge, and deviation parameter. We find that the deflection of light has correction terms coming from these parameters, which generalizes the Kerr deflection angle.

Modeling Large Deflections of Initially Curved Beams in Compliant Mechanisms Using Chained Beam-Constraint-Model

Abstract: Understanding and analyzing large and nonlinear deflections are the major challenges of designing compliant mechanisms. Initially, curved beams can offer potential advantages to designers of compliant mechanisms and provide useful alternatives to initially straight beams. However, the literature on analysis and design using such beams is rather limited. This paper presents a general and accurate method for modeling large planar deflections of initially curved beams of uniform cross section, which can be easily adapted to curved beams of various shapes. This method discretizes a curved beam into a few elements and models each element as a circular-arc beam using the beam constraint model (BCM), which is termed as the chained BCM (CBCM). Two different discretization schemes are provided for the method, among which the equal discretization is suitable for circular-arc beams and the unequal discretization is for curved beams of other shapes. Compliant mechanisms utilizing initially curved beams of circular-arc, cosine and parabola shapes are modeled to demonstrate the effectiveness of CBCM for initially curved beams of various shapes. The method is also accurate enough to capture the relevant nonlinear load-deflection characteristics.

Blast resistance and parametric study of sandwich structure consisting of honeycomb core filled with circular metallic tubes

Abstract: Hierarchical sandwich structures have been popularly investigated due to its promotion in structural stress and stiffness. A composite Honeycomb structure Filled with Circular Tubes (short as HFCT) was proposed in the previous study. In this paper, the blast resistance performances of sandwich plate filled with HFCT core (short as SP-HFCT) are investigated numerically by considering plastic dissipation energy, deflection of back face-sheet and deformation modes. The comparisons of performance between the general honeycomb sandwich plate (short as GHP) and the SP-HFCT illustrate that the composited filling mode can effectively improve blast resistant capacity by reducing the maximum deflection of the back plate and improving the ratio of plastic energy dissipated by cellular core to the total plastic energy dissipated by sandwich plate. Parametric analyses are performed to evaluate the influence of matching effect between container and filler, filling mode and blast loading on the resistance performance of SP-HFCT. The results show that a stronger honeycomb container filled with weaker circular tubes is a more favorable configuration of HFCT core. Meanwhile, by filling circular tubes into a buckling area, a considerable mass efficiency improvement with respect to deflection resistance can be obtained. With the increasing of stand-off distance, the effectiveness of SP-HFCT against blast loads will be boosted.

Polymer Optical Fiber for Angle and Torque Measurements of a Series Elastic Actuator's Spring

Abstract: Series elastic actuators (SEAs) can provide low output impedance, bandwidth close to the human movement, and direct measurement of torque through the spring deflection. These advantages enable the application of SEAs in human active orthosis and exoskeletons. However, conventional technologies to measure the spring deflection are bulky, inhibit natural pattern of movement or are sensitive to misalignments. This paper presents the application of polymer optical fiber (POF) as a sensor to measure the spring deflection to overcome some of the issues of conventional technologies, since it is compact, lightweight, and have electromagnetic immunity. Furthermore, the spring is employed to validate a torque sensor based on POF stress-optic effects. Results show high linearity of both sensors and mean squared errors below the encoder resolution employed as a reference on dynamic measurements.

Correlation-Based Estimation Method for Cable-Stayed Bridge Girder Deflection Variability under Thermal Action

Abstract: Thermal actions have a great influence on the girder deflection variability of long-span cable-stayed bridges. The main objective of this study is to investigate the variability of the brid...

Modeling and mechanical analysis of multiscale fiber-reinforced graphene composites: Nonlinear bending, thermal post-buckling and large amplitude vibration

Abstract: In this paper, a mathematical model was developed to predict the effective material properties of graphene nanoplatelets/fiber/polymer multiscale composites (GFPMC). The large deflection, post-buckling and free nonlinear vibration of graphene nanoplatelets-reinforced multiscale composite beams were studied through a theoretical study. The governing equations of laminated nanocomposite beams were derived from the Euler–Bernoulli beam theory with von Karman geometric nonlinearity. Halpin–Tsai equations and fiber micromechanics were used in hierarchy to predict the bulk material properties of the multiscale composite. Graphene nanoplatelets (GNPs) were assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. A semi-analytical approach was used to calculate the large static deflection and critical buckling temperature of multiscale multifunctional nanocomposite beams. A perturbation scheme was also employed to determine the nonlinear dynamic response and the nonlinear natural frequencies of the beams with clamped–clamped, and hinged–hinged boundary conditions. The effects of weight percentage of graphene nanoplatelets, volume fraction of fibers, and boundary conditions on the static deflection, thermal buckling and post-buckling and linear and nonlinear natural frequencies of the GFPMC beams were investigated in detail. The numerical results showed that the central deflection and natural frequency were significantly improved by a small percentage of GNPs. However, addition of GNPs led to a lower critical buckling temperature.

Evaluating mechanical performance of GFRP pipes subjected to transverse loading

Abstract: The main objective of this research is to investigate the damage progression and the failure mechanism of Glass-Fiber Reinforced-Plastic (GFRP) pipes subjected to compressive transverse loading. An experimental study is performed to observe the level of diametric deflection where failure takes place under transverse loading and also to monitor experienced failure mode. Then, conducted experimental study is simulated in commercial finite element software taking into account both interlaminar and intralaminar failure modes, simultaneously. The degree to which the pipe can withstand diametric deflection without experiencing any failure mode is extracted. Then, appropriate in-plane failure criteria are chosen for identifying the onset of in-plane failure mode while cohesive approach is employed for identifying the initiation of delamination as the out-of-plane failure mode. Results of numerical simulation reveal that the liner is debonded from its adjacent hoop layer at 27% diametric deflection which is in a reasonable agreement with experimentally observed 31%. Moreover, the magnitude of the reaction force at 5% diametric deflection is obtained as 1242 N which is in a good agreement with experimentally measured 1225 N. Therefore, a satisfactory level of accuracy is achieved in constructed model implying on the appropriate modeling of damage progression. Finally, a parametric study is conducted to investigate the influence of various effective parameters on the pipe resistance level against transverse loading wherein neither in-plane nor out-of-plane failure is experienced.

An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

Abstract: . A model for Quick Load Analysis of Floating wind turbines (QuLAF) is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: floater surge, heave, pitch and first tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are pre-computed in WAMIT and FAST, respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower base is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real time.

Flexural performance of hybrid GFRP-Steel reinforced concrete continuous beams

Abstract: This paper presents the experimental results of five large-scale hybrid glass fiber reinforced polymer (GFRP)-steel reinforced concrete continuous beams compared with two concrete continuous beams reinforced with either steel or GFRP bars as reference beams In addition, two simply supported concrete beams reinforced with hybrid GFRP/steel were tested The amount of longitudinal GFRP, steel reinforcements and area of steel bars to GFRP bars were the main investigated parameter in this study The experimental results showed that increasing the GFRP reinforcement ratio simultaneously at the sagging and hogging zones resulted in an increase in the load capacity, however, less ductile behaviour On the other hand, increasing the steel reinforcement ratio at critical sections resulted in more ductile behaviour, however, less load capacity increase after yielding of steel The test results were compared with code equations and available theoretical models for predicting the beam load capacity and load-deflection response It was concluded that Yoon's model reasonably predicted the deflection of the hybrid beams tested, whereas, the ACI4401R-15 equation underestimated the hybrid beam deflections It was also shown that the load capacity prediction for hybrid reinforced concrete continuous beams based on a collapse mechanism with plastic hinges at mid-span and central support sections was reasonably close to the experimental failure load