• A finite element analysis of impact damage in composite laminates

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (Cambridge University Press, 2012-12-01)
      In this work, stress-based and fracture mechanics criteria were developed to predict initiation and evolution, respectively, of intra- and inter-laminar cracking developed in composite laminates subjected to low velocity impact. The Soutis shear stress-strain semi-empirical model was used to describe the nonlinear shear behaviour of the composite. The damage model was implemented in the finite element (FE) code (Abaqus/Explicit) by a user-defined material subroutine (VUMAT). Delamination (or inter-laminar cracking) was modelled using interface cohesive elements and the splitting and transverse matrix cracks that appeared within individual plies were also simulated by inserting cohesive elements between neighbouring elements parallel to the fibre direction in each single layer. A good agreement was obtained when compared the numerically predicted results to experimentally obtained curves of impact force and absorbed energy versus time. A non-destructive technique (NDT), penetrant enhanced X-ray radiography, was used to observe the various damage mechanisms induced by impact. It has been shown that the proposed damage model can successfully capture the internal damage pattern and the extent to which it was developed in these carbon fibre/epoxy composite laminates.
    • Gradient-based optimization method for producing a contoured beam with single-fed reflector antenna

      Lian, Peiyuan; Wang, Congsi; Xiang, Binbin; Shi, Yu; Xue, Song; Xidian University; University of Chester; Chinese Academy of Sciences (IEEE, 2019-03-07)
      A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics (PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States (CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.
    • High speed CO2 laser surface modification of iron/cobalt co-doped boroaluminosilicate glass

      Hodgson, Simon D.; Waugh, David G.; Gillett, Alice R.; Lawrence, Jonathan; University of Chester (IOP Publishing, 2016-06-10)
      A preliminary study into the impact of high speed laser processing on the surface of iron and cobalt co-doped glass substrates using a 60 W continuous wave (cw) CO2 laser. Two types of processing, termed fill-processing and line-processing, were trialled. In fill-processed samples the surface roughness of the glass was found to increase linearly with laser power from an Sa value of 20.8 nm–2.1 μm at a processing power of 54 W. With line processing, a more exponential-like increase was observed with a roughness of 4 μm at 54 W. The change in surface properties of the glass, such as gloss and wettability, have also been measured. The contact angle of water was found to increase after laser processing by up to 64°. The surface gloss was varied between 45 and 100 gloss units (GUs).
    • High temperature performance of a piezoelectric micro cantilever for vibration energy harvesting

      Arroyo, Emmanuelle; Jia, Yu; Du, Sijun; Chen, Shao-Tuan; Seshia, Ashwin A. (IOP Publishing, 2016-12-06)
      Energy harvesters withstanding high temperatures could provide potentially unlimited energy to sensor nodes placed in harsh environments, where manual maintenance is difficult and costly. Experimental results on a classical microcantilever show a 67% drop of the maximum power when the temperature is increased up to 160 °C. This decrease is investigated using a lumped-parameters model which takes into account variations in material parameters with temperature, damping increase and thermal stresses induced by mismatched thermal coefficients in a composite cantilever. The model allows a description of the maximum power evolution as a function of temperature and input acceleration. Simulation results further show that an increase in damping and the apparition of thermal stresses are contributing to the power drop at 59% and 13% respectively.
    • Impact Damage Characteristics of Carbon Fibre Metal Laminates: Experiments and Simulation

      Shi, Yu; Soutis, Constantinos; Pinna, Christophe; University of Chester; The University of Sheffield; The University of Manchester
      In this work, the impact response of carbon fibre metal laminates (FMLs) was experimentally and numerically studied with an improved design of the fibre composite lay-up for optimal mechanical properties and damage resistance. Two different stacking sequences (Carall 3–3/2–0.5 and Carall 5–3/2–0.5) were designed and characterised. Damage at relatively low energy impact energies (≤30 J) was investigated using Ultrasonic C-scanning and X–ray Computed Tomography (X-RCT). A 3D finite element model was developed to simulate the impact induced damage in both metal and composite layers using Abaqus/Explicit. Cohesive zone elements were introduced to capture delamination occurring between carbon fibre/epoxy plies and debonding at the interfaces between aluminium and the composite layers. Carall 5–3/2–0.5 was found to absorb more energy elastically, which indicates better resistance to damage. A good agreement is obtained between the numerically predicted results and experimental measurements in terms of force and absorbed energy during impact where the damage modes such as delamination was well simulated when compared to non-destructive techniques (NDT).
    • In situ fabrication of carbon fibre–reinforced polymer composites with embedded piezoelectrics for inspection and energy harvesting applications

      Yan, Xue; Courtney, Charles; Bowen, Chris; Gathercole, Nicholas; Wen, Tao; Jia, Yu; Shi, Yu; Aerospace Research Institute of Material and Processing Technology; University of Bath; University of Chester
      Current in situ damage detection of fibre-reinforced composites typically uses sensors which are attached to the structure. This may make periodic inspection difficult for complex part geometries or in locations which are difficult to reach. To overcome these limitations, we examine the use of piezoelectric materials in the form of macro-fibre composites that are embedded into carbon fibre–reinforced polymer composites. Such a multi-material system can provide an in situ ability for damage detection, sensing or energy harvesting. In this work, the piezoelectric devices are embedded between the carbon fibre prepreg, and heat treated at elevated temperatures, enabling complete integration of the piezoelectric element into the structure. The impact of processing temperature on the properties of the macro-fibre composites are assessed, in particular with respect to the Curie temperature of the embedded ferroelectric. The mechanical properties of the carbon fibre–reinforced polymer composites are evaluated to assess the impact of the piezoelectric on tensile strength. The performance of the embedded piezoelectric devices to transmit and receive ultrasonic signals is evaluated, along with the potential to harvest power from mechanical strain for self-powered systems. Such an approach provides a route to create multi-functional materials.
    • In vitro mesenchymal stem cell response to a CO2 laser modified polymeric material

      Waugh, David G.; Hussain, Issam; Lawrence, Jonathan; Smith, Graham C.; Toccaceli, Christina; University of Chester; University of Lincoln (Elsevier, 2016-05-16)
      With an ageing world population it is becoming significantly apparent that there is a need to produce implants and platforms to manipulate stem cell growth on a pharmaceutical scale. This is needed to meet the socio-economic demands of many countries worldwide. This paper details one of the first ever studies in to the manipulation of stem cell growth on CO2 laser surface treated nylon 6,6 highlighting its potential as an inexpensive platform to manipulate stem cell growth on a pharmaceutical scale. Through CO2 laser surface treatment discrete changes to the surfaces were made. That is, the surface roughness of the nylon 6,6 was increased by up to 4.3 µm, the contact angle was modulated by up to 5° and the surface oxygen content increased by up to 1 atom%. Following mesenchymal stem cell growth on the laser treated samples, it was identified that CO2 laser surface treatment gave rise to an enhanced response with an increase in viable cell count of up to 60,000 cells/ml when compared to the as-received sample. The effect of surface parameters modified by the CO2 laser surface treatment on the mesenchymal stem cell response is also discussed along with potential trends that could be identified to govern the mesenchymal stem cell response.
    • Influencing the attachment of bacteria through laser surface engineering

      Gillett, Alice R.; Waugh, David G.; Lawrence, Jonathan; University of Chester (Laser Institute of America, 2015-10-31)
      Bacteria have evolved to become proficient at adapting to both extracellular and environmental conditions, which has made it possible for them to attach and subsequently form biofilms on varying surfaces. This has resulted in major health concerns and economic burden in both hospital and industrial environments. Surfaces which prevent this bacterial fouling through their physical structure represent a key area of research for the development of antibacterial surfaces for many different environments. Laser surface treatment provides a potential candidate for the production of anti-biofouling surfaces for wide ranging surface applications within healthcare and industrial disciplines. In the present study, a KrF 248 nm Excimer laser was utilized to surface pattern Polyethylene terephthalate (PET). The surface topography and roughness were determined with the use of a Micromeasure 2, 3D profiler. Escherichia coli (E. coli) growth was analysed at high shear flow using a CDC Biofilm reactor for 48 hours, scanning electron microscopy was used to determine morphology and total viable counts were made. Through this work it has been shown that the surface modification significantly influenced the distribution and morphology of the attached E. coli cells. What is more, it has been evidenced that the laser-modified PET has been shown to prevent E. coli cells from attaching themselves within the laser-induced micro-surface-features.
    • Integration and Characterisation of Piezoelectric Macro-Fibre Composite on Carbon Fibre Composite for Vibration Energy Harvesting

      Shi, Yu; Piao, Chenghe; Fadlaoui, Dounia; Alsaadi, Ahmed; Jia, Yu; University of Chester (IOPScience, 2019-11-01)
      Carbon fibre composite is a strong and a lightweight structural material with applications in automotive, aerospace, medical and industrial applications. The integration of piezoelectric transducer films onto the composite stack can add vibration energy harvesting capabilities to enable net-zero-power autonomous sensing for an otherwise purely mechanical structure. A PZT macro-fibre composite is co-cured with a carbon/epoxy pre-preg in order to manufacture the multi-functional composite plate. Without noticeably increasing profile, adding weight or compromising mechanical integrity, the resultant mechanical plate can recover power from vibrational excitations. With a volume of 13.5 cm3, a peak average power of 9.25 mW was recorded at 2.66 ms −2 . The normalised power density of 97 µW cm −3 m −2 s4 is comparable to some of the state-of-the-art PZT generators reported in the literature.
    • Interface Cohesive Elements to Model Matrix Crack Evolution in Composite Laminates

      Shi, Yu; Pinna, Christophe; Soutis, Constantinos; University of Chester; University of Sheffield; University of Manchester (Springer, 2013-10-02)
      In this paper, the transverse matrix (resin) cracking developed in multidirectional composite laminates loaded in tension was numerically investigated by a finite element (FE) model implemented in the commercially available software Abaqus/Explicit 6.10. A theoretical solution using the equivalent constraint model (ECM) of the damaged laminate developed by Soutis et al. was employed to describe matrix cracking evolution and compared to the proposed numerical approach. In the numerical model, interface cohesive elements were inserted between neighbouring finite elements that run parallel to fibre orientation in each lamina to simulate matrix cracking with the assumption of equally spaced cracks (based on experimental measurements and observations). The stress based traction-separation law was introduced to simulate initiation of matrix cracking and propagation under mixed-mode loading. The numerically predicted crack density was found to depend on the mesh size of the model and the material fracture parameters defined for the cohesive elements. Numerical predictions of matrix crack density as a function of applied stress are in a good agreement to experimentally measured and theoretically (ECM) obtained values, but some further refinement will be required in near future work.
    • Laser melting of NiTi and its effects on in-vitro mesenchymal stem cell responses

      Waugh, David G.; Lawrence, Jonathan; Chan, Chi-Wai; Hussain, Issam; Man, Hau-Chung; University of Chester ; University of Chester ; University of Lincoln ; University of Lincoln ; Hong Kong Polytechnic University (Woodhead Publishing, 2014-10-14)
    • Laser sealing of HDLPE film to PP substrate

      Shukla, Pratik; Lawrence, Jonathan; Waugh, David G.; University of Chester (2015-01)
    • Laser surface engineering of polymeric materials and the effects on wettability characteristics

      Waugh, David G.; Avdic, Dalila; Woodham, K. J.; Lawrence, Jonathan; University of Lincoln (Scrivener/John Wiley & Sons., 2014-12-23)
      Wettability characteristics are believed by many to be the driving force in applications relating to adhesion. So, gaining an in-depth understanding of the wettability characteristics of materials before and after surface treatments is crucial in developing materials with enhanced adhesion properties. This chapter details some of the main competing techniques to laser surface engineering followed by a review of current cutting edge laser surface engineering techniques which are used for wettability and adhesion modulation. A study is provided in detail for laser surface treatment (using IR and UV lasers) of polymeric materials. Sessile drop analysis was used to determine the wettability characteristics of each laser surface treated sample and as-received sample, revealing the presence of a mixed-state wetting regime on some samples. Although this outcome does not follow current and accepted wetting theory, through numerical analysis, generic equations to predict this mixed state wetting regime and the corresponding contact angle are discussed.
    • Laser surface engineering: Processes and applications

      Waugh, David G.; Lawrence, Jonathan; University of Chester (Woodhead Publishing, 2014-10-14)
      Lasers can alter the surface composition and properties of materials in a highly controllable way, which makes them efficient and cost-effective tools for surface engineering. This book provides an overview of the different techniques, the laser-material interactions and the advantages and disadvantages for different applications.
    • Laser surface induced roughening of polymeric materials and the effects on Wettability characteristics

      Waugh, David G.; Lawrence, Jonathan; Shukla, Pratik; University of Chester (2015-01-15)
      It has been thoroughly demonstrated previously that lasers hold the ability to modulate surface properties of polymers with the result being utilization of such lasers in both research and industry. With increased applications of wettability techniques within industries there is greater need of predicting related characteristics, post laser processing, since such work evaluates the effectiveness of these surface treatments. This paper details the use of a Synrad CO2 laser marking system to surface roughen polymeric materials, namely: nylon 6,6; nylon 12, polytetrafluoroethylene (PTFE) and polyethylene (PE). These laser-modified surfaces have been analyzed using 3D surface profilometry to ascertain the surface roughness with the wettability characteristics obtained using a wettability goniometer. From the surface roughness results, for each of the samples, generic wettability characteristics arising from laser surface roughening is discussed.
    • Laser surface modification of polymeric materials for microbiological applications

      Gillett, Alice R.; Waugh, David G.; Lawrence, Jonathan; University of Chester (Elsevier, 2016-04-15)
    • Laser surface structuring of ceramics, metals and polymers for biological applications: A review

      Shukla, Pratik; Waugh, David G.; Lawrence, Jonathan; University of Chester (Elsevier, 2014-10-14)
    • 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.