• Laser Surface Treatment of a Polymeric Biomaterial: Wettability Characteristics and Osteoblast Cell Response Modulation

      Waugh, David G.; Lawrence, Jonathan; University of Chester (Old City Publishing, 2014)
      Biotechnology has the potential to improve people's quality of life and holds the key to-many unmet clinical needs. In the UK alone the biotechnology market is worth £4.5 billion and estimates of future growth ranks from 10 to 15%. This growth can only be driven by the increased use of inexpensive and easy to manufacture polymeric biomaterials. Although polymer science is a rapidly developing area of research, it remains that one of the most intractable problems encountered in biotechnology is that the performance of polymeric biomaterials depends both upon the bulk and surface properties. In this book the authors describe Their work using lasers to modify the wettability characteristics of nylon 6,6 (as wetting often is the primary factor dictating the adhesion and bonding potential of materials) as a route to enhancing the area in terms of in vitro osteoblast cell response. What is more, modifying wettability characteristics in this way is shown to be a highly attractive means of estimating the biofunctionality of a polymer. The book demonstrates and explains how the generation of a biomimetic polymers and is surface using laser beams provides an in vitro platform on which to deposit and grow cells for either the development of implants or to reconstitute functional tissue. The correlative trends and generic characteristics which are identified are in the book between the laser treatment, wettability characteristics and osteoblast cell response of the nylon 6,6 provide a means to estimate the osteoblast cell response in vivo. The book shows clearly that laser surface modification of polymeric materials has tremendous potential for application within the field of regenerative medicine.
    • Laser surface treatment of polyamide and NiTi alloy and the effects on mesenchymal stem cell response

      Waugh, David G.; Lawrence, Jonathan; Shukla, Pratik; Chan, Chi-Wai; Hussain, Issam; Man, Hau-Chung; Smith, Graham C.; University of Chester ; University of Chester ; University of Chester ; Queen's University, Belfast ; University of Lincoln ; Hong Kong Polytechnic University ; University of Chester (2015-03-18)
      Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, surface treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare laser surface treatment of polyamide (Polyamide 6,6), using a 60 W CO2 laser, and NiTi alloy, using a 100 W fiber laser, and the effects of these treatments on mesenchymal stem cell response. The surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the laser surface treated samples, when compared to as-received samples, is evidenced in this work.
    • Lateral crushing and bending responses of CFRP square tube filled with aluminum honeycomb

      Liu, Qiang; Xu, Xiyu; Ma, Jingbo; Wang, Jinsha; Shi, Yu; Hui, David; Sun Yat-Sen University; Hunan University; University of Chester; University of New Orleans (Elsevier, 2017-03-18)
      This paper aims to investigate the lateral planar crushing and bending responses of carbon fiber reinforced plastic (CFRP) square tube filled with aluminum honeycomb. The various failure modes and mechanical characteristics of filled tube were experimentally captured and numerically predicted by commercial finite element (FE) package LS-DYNA, comparing to the hollow tubes. The filled aluminum honeycomb effectively improved the stability of progressive collapse during crushing, leading to both hinges symmetrically occurred along the vertical side. The experimental results showed that energy absorbed (EA) and specific energy absorption (SEA) of the filled CFRP tubes could be significantly increased to 6.56 and 4 times, respectively, of those measured for the hollow tubes without fillings under lateral crushing. Although an improvement of 32% of EA and 0.9% of SEA were obtained for the lateral bending, still the design using aluminum honeycomb as filling was remarkably capable to improve the mechanical characteristics of CFRP tube structure. A good agreement was obtained between experimentally measured and numerically predicted load-displacement histories. The FE prediction was also helpful in understanding the initiation and propagation of cracks within the filled CFRP structure.
    • Low-velocity impact of composite laminates: damage evolution

      Shi, Yu; Pinna, Christophe; Soutis, Constantinos; University of Chester; University of Sheffield; University of Manchester (Woodhead Publishing, 2016-02-19)
      This chapter presents modelling procedures used to simulate damage evolution in composite laminates used in aircraft structures when subjected to low-energy-level impact (≤15 J). Damage models for both initiation and evolution are first introduced by considering the individual damage modes of composite laminates in the form of intra- and inter-laminar damage mechanisms. The implementation of these damage criteria into the user subroutine Vumat of the finite element code Abaqus is then described for the simulation of damage development during low-velocity impact tests. Finite element prediction is then compared to experimental load-time measurements and damage extent obtained using X-rays as a non-destructive technique (NDT). Further development of the model is then presented by simulating matrix cracking evolution and splitting using a fracture mechanics-based criterion approach implemented into a cohesive zone element (CZE) formulation. Results from the extended model show clear improvement in terms of the accuracy of damage prediction, with experimental observations of the damage modes operating at ply-level providing further validation of the model. This can be used at an early stage of the design process of optimising laminate configurations used in aircraft structural applications.
    • Magnetically levitated autoparametric broadband vibration energy harvesting

      Kurmann, Lukas; Jia, Yu; Manoli, Yiannos; Woias, Peter; University of Applied Sciences and Arts Northwestern Switzerland; University of Chester; University of Freiburg (IOP Publishing, 2016-12-06)
      Some of the lingering challenges within the current paradigm of vibration energy harvesting (VEH) involve narrow operational frequency range and the inevitable non-resonant response from broadband noise excitations. Such VEHs are only suitable for limited applications with fixed sinusoidal vibration, and fail to capture a large spectrum of the real world vibration. Various arraying designs, frequency tuning schemes and nonlinear vibratory approaches have only yielded modest enhancements. To fundamentally address this, the paper proposes and explores the potentials in using highly nonlinear magnetic spring force to activate an autoparametric oscillator, in order to realize an inherently broadband resonant system. Analytical and numerical modelling illustrate that high spring nonlinearity derived from magnetic levitation helps to promote the 2:1 internal frequency matching required to activate parametric resonance. At the right internal parameters, the resulting system can intrinsically exhibit semi-resonant response regardless of the bandwidth of the input vibration, including broadband white noise excitation.
    • Maximizing Output Power in a Cantilevered Piezoelectric Vibration Energy Harvester by Electrode Design

      Du, Sijun; Jia, Yu; Seshia, Ashwin A.; University of Cambridge; University of Chester (IOP Publishing, 2015-12-01)
      A resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electric charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezoelectric material and metal electrode layers covering the entire surface area of the cantilever with no consideration provided to examining the trade-off involved with respect to maximizing output power. This paper reports on the theory and experimental verification underpinning optimization of the active electrode area of a cantilevered PVEH in order to maximize output power. The analytical formulation utilizes Euler-Bernoulli beam theory to model the mechanical response of the cantilever. The expression for output power is reduced to a fifth order polynomial expression as a function of the electrode area. The maximum output power corresponds to the case when 44% area of the cantilever is covered by electrode metal. Experimental results are also provided to verify the theory.
    • Micromachined cantilevers-on-membrane topology for broadband vibration energy harvesting

      Jia, Yu; Du, Sijun; Seshia, Ashwin A.; University of Cambridge; University of Chester (IOP Publishing, 2016-10-17)
      The overwhelming majority of microelectromechanical piezoelectric vibration energy harvesting topologies have been based on cantilevers, doubly-clamped beams or basic membranes. While these conventional designs offer simplicity, their broadband responses have been limited thus far. This paper investigates the feasibility of a new integrated cantilevers-on-membrane design that explores the optimisation of piezoelectric strain distribution and improvement of the broadband power output. While a classic membrane has the potential to offer a broader resonant peak than its cantilever counterpart, the inclusion of a centred proof mass compromises its otherwise high strain energy regions. The proposed topology addresses this issue by relocating the proof mass onto subsidiary cantilevers and combines the merits of both the membrane and the cantilever designs. Numerical simulations, constructed using fitted values based on finite element models, were used to investigate the broadband response of the proposed design in contrast to a classic plain membrane. Experimentally, when subjected to a band-limited white noise excitation, the new cantilevers-on-membrane harvester exhibited nearly two fold power output enhancement when compared to a classic plain membrane harvester of a comparable size.
    • A micromachined device describing over a hundred orders of parametric resonance

      Jia, Yu; Du, Sijun; Arroyo, Emmanuelle; Seshia, Ashwin A.; University of Cambridge; University of Chester (AIP Publishing, 2018-04-24)
      Parametric resonance in mechanical oscillators can onset from the periodic modulation of at least one of the system parameters, and the behaviour of the principal (1st order) parametric resonance has long been well established. However, the theoretically predicted higher orders of parametric resonance, in excess of the first few orders, have mostly been experimentally elusive due to the fast diminishing instability intervals. A recent paper experimentally reported up to 28 orders in a micromachined membrane oscillator. This paper reports the design and characterisation of a micromachined membrane oscillator with a segmented proof mass topology, in an attempt to amplify the inherent nonlinearities within the membrane layer. The resultant oscillator device exhibited up to over a hundred orders of parametric resonance, thus experimentally validating these ultra-high orders as well as overlapping instability transitions between these higher orders. This research introduces design possibilities for the transducer and dynamic communities, by exploiting the behaviour of these previously elusive higher order resonant regimes.
    • Modelling impact damage in composite laminates: A simulation of intra- and inter-laminar cracking

      Pinna, Christophe; Soutis, Constantinos; Shi, Yu; University of Chester; University of Sheffield; University of Manchester (Elsevier, 2014-04-12)
      In this work, stress- and fracture mechanics-based criteria are developed to predict initiation and evolution, respectively, of intra- and inter-laminar cracking developed in composite laminates subjected to a relatively low energy impact (⩽15 J) with consideration of nonlinear shear behaviour. The damage model was implemented in the finite element (FE) code (Abaqus/Explicit) through a user-defined material subroutine (VUMAT). Delamination (or inter-laminar cracking) was modelled using interface cohesive elements while splitting and transverse matrix cracks (intralaminar cracking) that appeared within individual plies were also simulated by inserting cohesive elements along the fibre direction (at a crack spacing determined from experiments for computing efficiency). A good agreement is obtained when the numerically predicted results are compared to both experimentally obtained curves of impact force and absorbed energy versus time and X-ray radiography damage images, provided the interface element stiffness is carefully selected. This gives confidence to selected fracture criteria and assists to identify material fracture parameters that influence damage resistance of modern composite material systems.
    • Modelling low velocity impact induced damage in composite laminates

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (SpringerOpen, 2017-07-26)
      The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction.
    • Modelling low velocity impact induced damage in composite laminates

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (Springer, 2017-07-26)
      The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction.
    • Modelling transverse matrix cracking and splitting of cross-ply composite laminates under four point bending

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (Elsevier, 2015-11-30)
      The transverse matrix cracking and splitting in a cross-ply composite laminate has been modelled using the finite element (FE) method with the commercial code Abaqus/Explicit 6.10. The equivalent constraint model (ECM) developed by Soutis et al. has been used for the theoretical prediction of matrix cracking and results have been compared to those obtained experimentally and numerically. A stress-based traction–separation law has been used to simulate the initiation of matrix cracks and their growth under mixed-mode loading. Cohesive elements have been inserted between the interfaces of every neighbouring element along the fibre orientation for all 0° and 90° plies to predict the matrix cracking and splitting at predetermined crack spacing based on experimental observations. Good agreement is obtained between experimental and numerical crack density profiles for different 90° plies. In addition, different mechanisms of matrix cracking and growth processes were captured and splitting was also simulated in the bottom 0° ply by the numerical model.
    • Modifications of surface properties of beta Ti by laser gas diffusion nitriding

      Ng, Chi-Ho; Chan, Chi-Wai; Man, Hau-Chung; Waugh, David G.; Lawrence, Jonathan; University of Chester; Queen's University; The Hong Kong Polytechnic University (AIP Publishing, 2016-03-31)
      b-type Ti-alloy is a promising biomedical implant material as it has a low Young’s modulus and is also known to have inferior surface hardness. Various surface treatments can be applied to enhance the surface hardness. Physical vapor deposition and chemical vapor deposition are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser surface treatment is a relatively new surface modification method to enhance the surface hardness but its application is still not accepted by the industry. The major problem of this process involves surface melting which results in higher surface roughness after the laser surface treatment.This paper will report the results achieved by a 100W CW fiber laser for laser surface treatment without the surface being melted. Laser processing parameters were carefully selected so that the surface could be treated without surface melting and thus the surface finish of the component could be maintained. The surface and microstructural characteristics of the treated samples were examined using x-ray diffractometry, optical microscopy, three-dimensional surface profile and contact angle measurements, and nanoindentation test.
    • Modifications of surface properties of beta Ti by laser gas diffusion nitriding

      Ng, Chi-Ho; Lawrence, Jonathan; Waugh, David G.; Chan, Chi-Wai; Man, Hau-Chung; University of Chester (Laser Institute of America, 2015-10)
      β -type Ti-alloy is a promising biomedical implant material as it has a low Young’s modulus but is also known to have inferior surface hardness. Various surface treatments can be applied to enhance the surface hardness. Physical vapour deposition (PVD) and chemical vapour deposition (CVD) are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser surface treatment is a relatively new surface modification method to enhance the surface hardness but its application is still not accepted by the industry. The major problem of this process involves surface melting which results in higher surface roughness after the laser surface treatment. This paper will report the results achieved by a 100 W CW fiber laser for laser surface treatment without the surface being melted. Laser processing parameters were carefully selected so that the surface could be treated without surface melting and thus the surface finish of the component could be maintained. The surface and microstructural characteristics of the treated samples were examined using X-ray diffractometry (XRD), optical microscopy (OM), 3-D surface profile & contact angle measurements and nano-indentation test.
    • Modulating the wettability characteristics and bioactivity of polymeric materials using laser surface treatment

      Waugh, David G.; Lawrence, Jonathan; Shukla, Pratik; University of Chester (Laser Institute of America, 2015-10)
      It has been thoroughly demonstrated previously that lasers hold the ability to modulate surface properties of materials with the result being utilization of such lasers in both research and industry. What is more, these laser surface treatments have been shown to affect the adhesion characteristics and bio-functionality of those materials. This paper details the use of a Synrad CO2 laser marking system to surface treat nylon 6,6 and polytetrafluoroethylene (PTFE). The laser-modified surfaces were analyzed using 3D surface profilometry to ascertain an increase in surface roughness when compared to the as-received samples. The wettability characteristics were determined using the sessile drop method and showed variations in contact angle for both the nylon 6,6 and PTFE. For the PTFE it was shown that the laser surface treatment gave rise to a more hydrophobic surface with contact angles of up to 150° being achieved. For the nylon 6,6, it was observed that the contact angle was modulated approximately ±10° for different samples which could be attributed to a likely mixed state wetting regime. The effects of the laser surface treatment on osteoblast cell and stem cell growth is discussed showing an overall enhancement of biomimetic properties, especially for the nylon 6,6. This work investigates the potential governing parameters which drives the wettability/adhesion characteristics and bioactivity of the laser surface treated polymeric materials.
    • Modulating the wettability characteristics and bioactivity of polymeric materials using laser surface treatment

      Waugh, David G.; Lawrence, Jonathan; Shukla, Pratik; University of Chester (AIP Publishing, 2016-03-31)
      It has been thoroughly demonstrated previously that lasers hold the ability to modulate surface properties of materials with the result being utilization of such lasers in both research and industry. What is more, these laser surface treatments have been shown to affect the adhesion characteristics and bio-functionality of those materials. This paper details the use of a Synrad CO2 laser marking system to surface treat nylon 6,6 and polytetrafluoroethylene (PTFE). The laser-modified surfaces were analyzed using 3D surface profilometry to ascertain an increase in surface roughness when compared to the as-received samples. The wettability characteristics were determined using the sessile drop method and showed variations in contact angle for both the nylon 6,6 and PTFE. For the PTFE it was shown that the laser surface treatment gave rise to a more hydrophobic surface with contact angles of up to 150° being achieved. For the nylon 6,6, it was observed that the contact angle was modulated approximately ±10° for different samples which could be attributed to a likely mixed state wetting regime. The effects of the laser surface treatment on osteoblast cell and stem cell growth is discussed showing an overall enhancement of biomimetic properties, especially for the nylon 6,6. This work investigates the potential governing parameters which drives the wettability/adhesion characteristics and bioactivity of the laser surface treated polymeric materials.
    • Multimodal Shear Wave Deicing Using Fibre Piezoelectric Actuator on Composite for Aircraft Wings

      Shi, Yu; Jia, Yu; University of Chester
      The formation and accretion of ice on aircraft wings during flight can be potentially disastrous and existing in-flight deicing methods are either bulky or power consuming. This paper investigates the use of shear wave deicing driven by a macro fibre piezoelectric composite actuator on a composite plate typically used for aircraft wings. While the few existing research on this novel deicing approach focused on either theoretical studies or single frequency mode optimization that required high-excitation amplitudes, this study revealed that the use of multimodal excitation through broadband frequency sweeps has the potential to promote the chance of shear stress induced deicing at a relatively small excitation amplitude. The results reported here form the foundation for a pathway towards low power and lightweight deicing mechanism for in-flight aircraft wings.
    • Multiphysics vibration FE model of piezoelectric macro fibre composite on carbon fibre composite structures

      Jia, Yu; Wei, Xueyong; Xu, Liu; Wang, Congsi; Lian, Peiyuan; Xue, Song; Alsaadi, Ahmed; Shi, Yu; University of Chester; Xi'an Jiaotong University; Xidian University (Elsevier, 2018-12-21)
      This paper presents a finite element (FE) model developed using commercial FE software COMSOL to simulate the multiphysical process of pieozoelectric vibration energy harvesting (PVEH), involving the dynamic mechanical and electrical behaviours of piezoelectric macro fibre composite (MFC) on carbon fibre composite structures. The integration of MFC enables energy harvesting, sensing and actuation capabilities, with applications found in aerospace, automotive and renewable energy. There is an existing gap in the literature on modelling the dynamic response of PVEH in relation to real-world vibration data. Most simulations were either semi-analytical MATLAB models that are geometry unspecific, or basic FE simulations limited to sinusoidal analysis. However, the use of representative environment vibration data is crucial to predict practical behaviour for industrial development. Piezoelectric device physics involving solid mechanics and electrostatics were combined with electrical circuit defined in this FE model. The structure was dynamically excited by interpolated vibration data files, while orthotropic material properties for MFC and carbon fibre composite were individually defined for accuracy. The simulation results were validated by experiments with <10﹪ deviation, providing confidence for the proposed multiphysical FE model to design and optimise PVEH smart composite structures.
    • A New Electrode Design Method in Piezoelectric Vibration Energy Harvesters to Maximize Output Power

      Du, Sijun; Jia, Yu; Chen, Shao-Tuan; Zhao, Chun; Sun, Boqian; Arroyo, Emmanuelle; Seshia, Ashwin A.; University of Cambridge; University of Chester (Elsevier, 2017-07-19)
      A resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electrical charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezoelectric materials and metal electrode layers covering the entire surface area of the cantilever with no consideration provided to examine the trade-off involved with respect to maximize output power. This paper reports on the theory and experimental verification underpinning optimization of the active electrode area in order to maximize output power. The calculations show that, in order to maximize the output power of a PVEH, the electrode should cover the piezoelectric layer from the peak strain area to a position, where the strain is a half of the average strain in all the previously covered area. With the proposed electrode design, the output power can be improved by 145% and 126% for a cantilever and a clamped-clamped beam, respectively. MEMS piezoelectric harvesters are fabricated to experimentally validate the theory.
    • A Numerical Feasibility Study of Kinetic Energy Harvesting from Lower Limb Prosthetics

      Jia, Yu; Wei, Xueyong; Pu, Jie; Xie, Pengheng; Wen, Tao; Wang, Congsi; Lian, Peiyuan; Xue, Song; Shi, Yu; Aston University; University of Chester; Xidian University; Xi'an Jiaotong University (MDPI, 2019-10-10)
      With the advancement trend of lower limb prosthetics headed towards bionics (active ankle and knee) and smart prosthetics (gait and condition monitoring), there is an increasing integration of various sensors (micro-electromechanical system (MEMS) accelerometers, gyroscopes, magnetometers, strain gauges, pressure sensors, etc.), microcontrollers and wireless systems, and power drives including motors and actuators. All of these active elements require electrical power. However, inclusion of a heavy and bulky battery risks to undo the lightweight advancements achieved by the strong and flexible composite materials in the past decades. Kinetic energy harvesting holds the promise to recharge a small on-board battery in order to sustain the active systems without sacrificing weight and size. However, careful design is required in order not to over-burden the user from parasitic effects. This paper presents a feasibility study using measured gait data and numerical simulation in order to predict the available recoverable power. The numerical simulations suggest that, depending on the axis, up to 10s mW average electrical power is recoverable for a walking gait and up to 100s mW average electrical power is achievable during a running gait. This takes into account parasitic losses and only capturing a fraction of the gait cycle to not adversely burden the user. The predicted recoverable power levels are ample to self-sustain wireless communication and smart sensing functionalities to support smart prosthetics, as well as extend the battery life for active actuators in bionic systems. The results here serve as a theoretical foundation to design and develop towards regenerative smart bionic prosthetics.