Advances in Experimental Mechanics

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Authors: Steve Haake
Abstract: This paper aims to define sports engineering through the use of historical and contemporary examples. The historical development of the technology in the sprint and in the javelin are discussed, from their introduction to the Olympics over two and a half thousand years ago to the current day. The rules pertaining to tennis racquets are described and the ways in which manufacturers and researchers attempt to maximize performance using technology are examined. Two models for a tennis racquet are shown, one in which the racquet is modelled as a rigid body and one in which it is modelled as a flexible beam. Use of the models shows that further advances in racquet technology using stiffer and lighter materials are unlikely to speed the game up. It was concluded that technology can be used by athletes and manufacturers to enhance performance. Equally, the ruling bodies of sport can also use technology to limit performance, leading to a delicate balance between technology and tradition.
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Authors: Takashi Yokoyama
Abstract: Compressive stress-strain characteristics of carbon/epoxy laminated composites in the through-thickness direction at strain rates of over 1000/s were evaluated using the standard split Hopkinson pressure bar. Three carbon/epoxy laminated composites (i.e., unidirectional, cross-ply and woven) with almost the same thickness were tested at room temperature. Small solid cylindrical specimens were machined such that the direction of the compression loading was perpendicular to the fiber direction of the laminates. The effects of strain rate and reinforcement geometry on the secant modulus at 1% strain, ultimate compressive strength and strain, and total strain energy to failure were examined in detail.
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Authors: Peter Stanley
Abstract: The paper provides a picture of the changes and advances in the field of strain measurement, as represented by the contents of the journal “strain”, from its inception in 1965 to the present day.
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Authors: Thomas H. Hyde, W. Sun
Abstract: This paper describes some recent work on the stress analyses and failure prediction of some typical pressurised high temperature components under creep conditions, including plain pipes, pipe bends, branch connections and welds etc, in the main steam pipework of power plant. The materials used are typically low alloy ferritic CrMoV steels. Experimental creep testing methods, and the procedures used for generating the material properties in creep and damage constitutive equations, are briefly described. Some typical numerical results are presented to illustrate the main characteristics of the behaviour of these components and to demonstrate the effects of geometry, material properties and loading modes on stress distributions and failure life predictions. The emphasis of the paper is on welded components.
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Authors: R.H. Cornish, M. Srai, P. Cowen, M. Welch, Mike Daniels
Abstract: This paper reports results from a stress, acoustics and vibration investigation of the ride and driveline components of a new 2-seater sports car. The work was aimed at giving design assurance information to designers and vehicle engineers working to compressed timescales. The paper focuses on two particular areas: design of the power train for NVH refinement, and design analysis of a suspension wishbone. In the first case, a dynamic model of drive shaft torsion effects was created to understand design relationships needed for high power, high torque performance car. In the second case, an investigation was made into the integrity of a suspension wishbone component when gauge thickness was reduced from 3 mm to 2 mm. The work described was carried out in a joint industry academic venture sponsored by Knowledge Transfer Partnership (KTP). It is from this background that the authors give some perspectives on vehicle development.
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Authors: Alan MacBeath, Andrea Cardoni, Lorna Smith, Margaret Lucas
Abstract: The design of high power ultrasonic cutting devices is based on tuning a blade to a longitudinal mode of vibration at a low ultrasonic frequency, usually in the range 20-100 kHz. To achieve the required cutting amplitude, gain is designed into the blade via profiling. It is expected that the use of higher-gain blades could enable longitudinal-mode guillotine-type cutting of a range of materials traditionally difficult to cut using this technology. Using a conventional high-gain blade, a feasibility study of ultrasonic cutting of bone is conducted using compact tension specimens of bovine femur. Finite element (FE) models are created, based on the assumption that the ultrasonic blade causes a crack to propagate in a controlled mode 1 opening. The models are compared with the experimental data collected from ultrasonic bone cutting experiments. Although the proposed cutting mechanism is supported by the data, the blade gain is insufficient to enable through cutting of long bone or other difficult to cut materials. Consequently, the paper examines the relationship between gain, profile, stress and nodal position for a range of ultrasonic cutting blades with increased gain.
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Authors: José Manoel Balthazar, Reyolando Manoel Lopes Rabelo da Fonseca Brasil, F.J. Garzeri
Abstract: We present measurements of the non-linear oscillations of a portal frame foundation for a non-ideal motor. We consider a three-time redundant structure with two columns, clamped in their bases and a horizontal beam. An electrical unbalanced motor is mounted at mid span of the beam. Two non-linear phenomena are studied: a) mode saturation and energy transfer between modes; b)interaction between high amplitude motions of the structure and the rotation regime of a real limited power motor. The dynamic characteristics of the structure were chosen to have one-to-two internal resonance between the anti-symmetrical mode (sway motions) and the first symmetrical mode natural frequencies. As the excitation frequency reaches near resonance conditions with the 2nd natural frequency, the amplitude of this mode grows up to a certain level and then it saturates. The surplus energy pumped into the system is transferred to the sway mode, which experiences a sudden increase in its amplitude. Energy is transformed from low amplitude high frequency motion into high amplitude low frequency motion. Such a transformation is potentially dangerous. We consider the fact that real motors, such as the one used in this study, have limited power output. In this case, this energy source is said to be non-ideal, in contrast to the ideal source whose amplitude and frequency are independent of the motion of the structure. Our experimental research detected the Sommerfeld Effect: as the motor accelerates to reach near resonant conditions, a considerable part of its output energy is consumed to generate large amplitude motions of the structure and not to increase its own angular speed. For certain parameters of the system, the motor can get stuck at resonance not having enough power to reach higher rotation regimes. If some more power is available, jump phenomena may occur from near resonance to considerably higher motor speed regimes, no stable motions being possible between these two.
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Authors: M.F. Harper, M. Thompson
Abstract: Noise from a source such as an engine or gearbox can travel through a surrounding structure by many routes. It can be very difficult to reduce noise transmission to the environment or to operators or passengers, because many paths contribute to the transmission and it may not be clear which need to be treated. In order to apply effective control measures, it is very helpful to start with knowledge of the relative importance of the various possible paths. We report on a method that allows the strengths of the different paths to be quantified and ranked in order of importance, without having to dismantle or disconnect the system. Having measured these, and then having measured the levels of noise being injected into each path by the engine or gearbox, the contribution of each path to transmitted noise can then be estimated. Finally the noise reduction obtained by treating any desired combination of paths can be predicted. We refer to the method as “Transmission Path Audit” (TPA). The method was applied to an operating wind turbine that was giving noise problems. A TPA was carried out: it indicated that the problem was due to the turbine blades and tower, which between them radiated the bulk of the noise at three different tonal frequencies. Based on these results, damping treatments were applied to the blades and tower, and noise radiation was reduced to acceptable levels. The TPA method has very general applicability, and can be used to characterise noise transmission through a wide range of structures. It is likely to be particularly useful in tracing transmission paths through vehicles, from the power plant to the passenger space. Its novelty lies in its being entirely non-intrusive.
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Authors: Irina Trendafilova, M. Imbabi
Abstract: This research considers the problem for vibration based damage diagnosis in reinforced concrete slabs. It suggests the analysis of the time domain measured accelerations for the purposes of fault detection and quantification. The measured accelerations from different damage states of the slab are first subjected to initial transforms to bring them to vectors with reasonable component number. These vectors are further transformed using principal components analysis (PCA), which brings their coordinates down to two. In addition to reducing the number of measured acceleration points, PCA clusters the new vectors making distinguishable the different damage states. The results from the application of the suggested method convincingly demonstrate that the method can be applied for fault detection as well as for estimating the damage extent.
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Authors: Din Geng Li, Ji Guang Cao, Jun Wen Wang, Chuan Yao Chen
Abstract: In this paper, a new type of vibration structure (i.e. swing frame) of vertical dynamic balancing machine is designed, which is based on the analysis of traditional double-plane vertical dynamic balancing machine’s swing frame. The static unbalance and couple unbalance can be separated effectively by using the new dynamic balancing machine with the new swing frame. The modal and harmonic responses are analyzed by using the ANSYS7.0. By comparing the finite element modal analysis with the experimental modal analysis, the natural frequencies and vibration modes are found out, which can provide the dynamics direction for designing vertical dynamic balancing machine. The new dynamic balancing machine can measure static unbalance and couple unbalance directly, and the influence between them is faint. The practical result indicates that the new vertical dynamic balancing machine is suitable for inertial measurement of flying objects, and can overcome the shortcomings of traditional double-plane vertical dynamic balancing machines, in which the effect of plane-separation is inferior. The vertical dynamic balancing machine with the new vibration structure can be widely used in the future application.
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