This paper presents a fractional drift-diffusion (Fr-DD) model to characterize the transconductance characteristics of a 6,13-bis(triisopropylsilylethynyl)pentacene TIPS-pentacene based organic field effect transistor (OFET) when bending effects are taken into account. The Fr-DD model is proposed by fractionalizing the diffusive current density in the carrier continuity equations of the conventional drift-diffusion (DD) model. Gummel’s iteration is utilized to decouple the governing equations of the Fr-DD model. The solved hole concentration and electrostatic potentials on the metal-semiconductor interface are employed to approximate the terminal current flow and generate the transconductance characteristics of the OFET. Compared to the conventional DD model, the Fr-DD model does not need to consider the density of trap states (DoS) since its fractional derivative order in relation to material type, boundary conditions and bending radius can be obtained directly by fitting limited experimental data. In addition, a comparison with experimental data reveals that the Fr-DD model can result in much more accurate predictions on transconductance characteristics than the conventional DD model, especially in the subthreshold and low gate-source voltage regions of the OFET.

Within industrial manufacturing most processing steps are accompanied by transporting and positioning of workpieces. The active interfaces between handling system and workpiece are industrial grippers, which often are driven by pneumatics, especially in small scale areas. On the way to higher energy efficiency and digital factories, companies are looking for new actuation technologies with more sensor integration and better efficiencies. Commonly used actuators like solenoids and electric engines are in many cases too heavy and large for direct integration into the gripping system. Due to their high energy density shape memory alloys (SMA) are suited to overcome those drawbacks of conventional actuators. Additionally, they feature self-sensing abilities that lead to sensor-less monitoring and control of the actuation system. Another drawback of conventional grippers is their design, which is based on moving parts with linear guides and bearings. These parts are prone to wear, especially in abrasive environments. This can be overcome by a compliant gripper design that is based on flexure hinges and thus dispenses with joints, bearings and guides. In the presented work, the development process of a functional prototype for a compliant gripper driven by a bistable SMA actuation unit for industrial applications is outlined. The focus lies on the development of the SMA actuator, while the first design approach for the compliant gripper mechanism with solid state joints is proposed. The result is a working gripper-prototype which is mainly made of 3D-printed parts. First results of validation experiments are discussed.

Fibre-reinforced polymer (FRP) composite materials are limited in high temperature applications by the matrix glass transition temperature, T g . At and above this temperature, significant mechanical performance is lost, and degradation processes accelerated. This research explores the use of internal passages, or vascules, within the laminate to carry a coolant fluid, absorbing heat energy and cooling the material. A custom thermal chamber and four-point flexural test fixture were developed to perform in-situ thermo-mechanical testing. Vascular and non-vascular carbon/epoxy specimens were manufactured, containing arrays of four 1.1 mm diameter vascules. Specimens were exposed to temperatures from ambient to 170 °C (T g = 200 °C). Flexural modulus varied little with temperature across all tests. Non-vascular specimens at 170 °C showed a reduction in ultimate strength of 21 % compared to under ambient conditions. The presence of vascules caused a small improvement in flexural modulus and strength, due to displacement of a small number of 0° fibre tows further from the neutral axis as a result of the manufacturing process. At 15 L·min −1 coolant flow, vascular specimens showed full retention of strength compared to non-vascular specimens at ambient, demonstrating the potential mechanical performance benefits.

In this paper the design of a linear long-stroke quasi-constant force compliant mechanism (CM) is presented and discussed. Starting from a flexure-based slider-crank mechanism, providing the required constant force within a rather limited deflection range, the paper reports about the shape optimization carried out with the specific aim of extending the available CM operative range. The proposed device is suitable in several precision manipulation systems, which require to maintain a constant-force at their contact interface with the manipulated object. Force regulation is generally achieved by means of complex control algorithms and related sensory apparatus, resulting in a flexible behavior but also in high costs. A valid alternative may be the use of a purposely designed CM, namely a purely mechanical system whose shape and dimensions are optimized so as to provide a force-deflection behavior characterized by zero stiffness. In the first design step, the Pseudo-Rigid Body (PRB) method is exploited to synthesize the sub-optimal compliant configuration, i.e. the one characterized by lumped compliance. Secondly, an improved design alternative is evaluated resorting to an integrated software framework, comprising Matlab and ANSYS APDL, and capable of performing non-linear structural optimizations. The new embodiment makes use of a variable thickness beam, whose shape and dimensions have been optimized so as to provide a constant reaction force in an extended range. Finally, a physical prototype of the beam-based configuration is produced and tested, experimentally validating the proposed design method.

Functionally graded compliant mechanisms can be fabricated with additive manufacturing technology by engineering the microstructural and compositional gradients at selected locations resulting in compositionally graded zones of higher and lower flexibility. The local compliance depends on the geometry of the structure as well as the material property in the selected region. As Nitinol (NiTi) is well suited for applications requiring compliance, the critical transformation stress and the superelastic modulus of elasticity are crucial parameters for defining the local compliance. To understand the behavior at the interface between two different material compositions, three models of gradient change between the alloys are analyzed: step change, linear and polynomial gradients. In addition to localize the deformation in the interface, three different flexure designs in the interface are analyzed. This paper will address a methodology for modeling and parametrization of material properties and transition at the interface, for different flexure designs. The combined effort in the interface of the functional grading and the geometry will be used for the design of monolithic self-deployable structures, initially folded in compact shape. The design motivation comes from the self-deploying mechanisms inspired by insects’ wings.

Large loads due to fluid-structure interaction can lead to high bending stresses and fatigue failure in wings and wind turbine blades. A solution for the mentioned problem is using a bistable composite laminate for load alleviation. A bistable composite laminate is capable of attaining two statically stable shapes, and it can be designed to alleviate a critical load, such as wind gust, by snapping from one stable position to the other. Piezocomposite actuators can be used to reverse the snap-through and bring back the structure to its original optimal aerodynamic shape, after the gust load is alleviated. However, there will always be a limit on the size of the piezocomposite actuator used; hence, severe force and energy constraints exist to achieve the snap-through. In this context, this paper focuses on the minimum required actuation energy for performing snap-through of a bistable structure. The paper shows how the required energy for cross-well transfer varies as a function of damping ratio and frequency ratio at specific harmonic force amplitude when the system is externally disturbed with a band-limited noise signal. A band-limited noise signal is chosen to model external/ambient disturbances. This paper uses the Duffing-Holmes equation as a one-degree-of-freedom representative model of a bistable structure. This equation is numerically solved to calculate the required energy for cross-well oscillation under different system and forcing conditions. Various non-dimensional parameters are used to highlight interesting phenomena. It is found that the domain of low energy regions decreases by increasing the level of noise.

We present a symmetric five-bar compliant mechanism for the displacement amplification of mechanical vibration. When the proposed mechanism is connected to an energy harvester, amplification of the input excitation vibration amplitude leads to an increase in the harvested power. Displacements in the compliant mechanism are caused by deflections in its flexure hinges. The flexure hinges we use are either of the right-circular, or the corner-filleted types. The mechanism is analyzed using energy methods. The displacement amplification was verified analytically and numerically using a finite element model. Through our model we present relations governing the displacement amplification in terms of the design parameters, such as the geometry of the mechanism, the flexure hinges dimensions, in addition to the load caused by the harvester. The effects of the flexure hinge dimensions on displacement amplification, are also presented.

Flexible needles that can be steered within soft tissues are a promising approach to precisely reach target locations, thereby can significantly benefit needle based surgical procedures such as brachytherapy and biopsy. Several design approaches have been suggested to increase needle flexibility that include bevel-tip needles, kinked needles and flexure-based needles. These needles when inserted into a soft materials takes a curved path. This curved path can be controlled while inserting by rotating the needle at its base. In this work another approach to control the curved path was explored. Here the needle body was attached with a shape memory alloy (SMA) actuator close the needle tip that when actuated bends the needle and thereby leads to a curved path inside soft tissue. A prototype of the SMA actuated needle was developed and the working principle was demonstrated in air, tissue-mimicking gel, and pig liver. Moreover, the effect of actuator wire diameter on the needle behavior were studied.

This paper presents an initial experimental and computational investigation of a flow-induced vibration energy harvester with a compliant flexure mechanism. This energy harvester utilizes the aeroelastic flutter phenomenon to convert the flow energy to vibrational energy which can be converted into useful electrical power using piezoelectric transducers. However, unlike previous flutter-based flow energy harvesters [1] which require assembling multiple components to create the necessary aeroelastic arrangement, the device described here utilizes a monolithic, compact design to achieve the same. In this paper, we propose a flexure design for this device and model it using analytic methods and finite element simulations. A proof of concept energy harvester incorporating this flexure design has been fabricated and experimentally investigated in wind tunnel testing.

Alfenol (Fe x Al 100−x ) is an alloy similar to Galfenol (Fe-Ga alloys) in crystal lattice structure and magnetostriction trend (peaking at ∼20% composition). Although single-crystal Fe 80 Al 20 exhibits lower magnetostriction (∼184 ppm, about half of Fe 80 Ga 20 ), its magneto-elastic coupling coefficient is on par with that of Fe-Ga. In addition, characteristics such as machinability and rollability are superior to that of Galfenol, making it possible to achieve textured sheets (thickness∼200 μm) which, while having a high elastic modulus, are very flexible. Furthermore, Aluminum is non toxic, cheap (∼1% the cost of Ga) and is available in abundance. These attributes make Alfenol an ideal candidate for a bio-inspired whisker-like tactile sensor (mimicking mystacial vibrissae of cats, sea lions, etc.). This work deals with the design and development of an accurate, cost efficient, real-time, and non-invasive sensor prototype that tracks displacements, vibrations and scour on bridge piers with minimal signal conditioning. Making such a sensor is possible thanks to Alfenol’s linear response to strain in the presence of appropriate bias magnets. The change in its magnetic state due to inverse magnetostriction from applied bending stresses will be observed using Hall Effect sensors to derive deflection information. A protocol to manufacture rolled and textured Alfenol whisker samples will be presented in this research. The effect of bias conditions on sensor performance will be studied empirically and by using multi-physics simulations. Optimization of the sensor by varying the dimensions of the whisker, and its correlation to flux leakage will also be examined followed by an effort to understand the micro-magnetic response of Alfenol to mechanical stimulation. Finally, results from using this biomimetic sensor to measure displacements and vibrations, and its viability to be used as a flow sensor will be discussed. The robustness of this sensor has been exploited to develop a novel real-life application to provide an early warning system for bridge pier scour due to soil transportation during a weather event. The effectiveness of these sensors for scour detection in riverbeds will subsequently be simulated in a water flume and analyzed.

Shape Memory Alloy (SMA) actuator wires are often discussed in the context of multi-functional materials. This is because the temperature-induced phase transformation causes a significant (∼4%) contraction and a corresponding change in resistance. When a restoring force such as a pre-stretched spring is placed in series with an SMA wire, the contraction creates a repeatable actuation force, and the resistance provides measurement of the strain the wire, or structural (spring) deflection. Work has already been presented to demonstrate the stress, strain, and resistance characteristics of a single SMA actuator wire in series with a spring flexure under different pre-stresses and heating power input frequencies. Also, a method has been presented to linearly approximate the resistance vs strain characteristic, thus providing a direct mapping from SMA wire resistance to flexure deflection. This mapping method has been tested in the context of a simple PID controller used to position a flexure in series with a single SMA. This paper expands previous work by characterizing a system consisting of a spring flexure in series with two opposing SMA wires. Such an opposing SMA configuration is relevant to embedded SMA applications and gives the potential to increase cycling frequency by providing an active restoring force. The characterization results show that coupling SMA wires introduces alters the resistance vs strain characteristics of both wires because the second SMA wire essentially becomes a non-linear, hysteretic spring in series with the first. However, knowledge of the physics behind the complicated behavior enables sensible calibration schemes to be developed to accurately map resistance to strain for simultaneous sensing and actuating applications.

A novel Lewis acid-catalysed self-healing system is investigated for implementation in epoxy-based fibre reinforced polymer (FRP) composite materials. The catalyst, scandium(III) triflate, is selected using a qualitative approach and subsequently embedded with pre-synthesised epoxy-solvent loaded microcapsules, into an epoxy resin. Healing is initiated when microcapsules are ruptured at the onset of crack propagation. The epoxy monomer healing agent contained within, actively undergoes ring-opening polymerisation (ROP) on contact with the locally placed catalyst, forming a new polymer to bridge the two fractured crack surfaces. Self-healing performance is quantified using tapered double cantilever beam (TDCB) epoxy resin test specimens and the effects of microcapsule loading, microcapsule content and healing temperature are all independently considered. As an initial proof of concept study, results show that a material recovery value of greater than 80% fracture strength is achieved for this novel Lewis acid-catalysed self-healing epoxy resin. The same self-healing agent system was subsequently demonstrated in a larger scale FRP component by incorporating both a microcapsule and hollow glass fibre (HGF) delivery system within an FRP laminate using a End-Notched Flexure (ENF) test configuration.

Piezoelectric-based positioners are incorporated into stereotaxic devices for microsurgery, scanning tunneling microscopes for the manipulation of atomic and molecular-scale structures, nanomanipulator systems for cell microinjection and machine tools for semiconductor-based manufacturing. This wide range of applications requires the design and development of large load capacity, long stroke and compact positioning stages without compromising high speed and precision. Although several precision positioning systems have been developed for planar motion, most are neither suitable nor readily lend themselves to provide long travel range with large load capacity in vertical axis because of their weights, size, design and embedded actuators. To address the limitations of the traditional technologies, a novel positioner is being developed specifically for vertical axis motion based on a piezoworm arrangement in flexure frames. Analytical calculations and finite element analysis are used to optimize the design of the lifting platform to provide maximum thrust force while maintaining a compact size. To make a stage frame more compact, the actuator is integrated into the stage body which mainly consists of a moveable component outside a rigid frame. The clamps are designed such that no power is needed to maintain a fixed vertical position, holding the payload against the force of gravity.

In the present work, apart from developing a processing method for multi-scale laminates, characterization efforts are focused on finding longitudinal, transverse and in-plane shear modulus using flexure and in-plane shear testing of unidirectional, [0°] 10 , and multidirectional, [±45°] 2s , laminates. A comparison of the above mentioned macroscale properties is presented for three types of composites, i.e., composites embedded with functionalized nanotubes, un-functionalized or pristine nanotubes and base composite without nanotubes. Classical laminate theory is used to model a representative laminate system. Transverse and longitudinal properties are presented and compared with experimental observations. Transmission and scanning electron microscopy is performed to study the nanotube dispersion and the morphology of fracture surfaces at different length scales.