CERES :: Browsing by Author "Khan, Muhammad Ali"

Browsing by Author "Khan, Muhammad Ali"

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Open Access
3-3 piezoelectric metamaterial with negative and zero Poisson's ratio for hydrophones applications
(Elsevier, 2018-12-18) Khan, Kamran Ahmed; Khan, Muhammad Ali
This study presents the electromechanical properties of the 3-3 piezoelectric metamaterial based on variants of honeycomb (HC) structure. Three kinds of three-dimensional (3D) elastically anisotropic and piezoelectrically active HC structures were introduced, namely, conventional HC (3D-CHC), a re-entrant HC (3D-RE) and a semi-re-entrant HC (3D-SRE). Highly porous 3D finite element models of the mentioned three kinds of metamaterials were developed and the role of ligament orientation on their effective elastic, piezoelectric and dielectric properties was completely characterized. The intrinsic symmetry of HC structure was utilized and simplified mixed boundary conditions equivalent to periodic boundary conditions were recognized. In comparison to their bulk constituent, all the 3-3 type piezoelectric HC networks exhibited an enhanced response, especially for the longitudinal poling. The normalized figures of merit show a mild dependence on the angle θ and the underlying deformation mechanisms associated with the zero, positive and negative Poisson’s ratios. Figures of merit such as hydrostatic strain coefficient (dh" role="presentation">), the hydrostatic figure of merit (dh.gh" role="presentation">) and the acoustic impedance (Z" role="presentation">) reached their best values at small angles, i.e., θ = 30°. Longitudinally poled networks exhibited four order of magnitude increase in their hydrostatic figure of merit (foam to solid ratio >10,000) and one order of magnitude decrease in the acoustic impedance indicating their applicability for the design of hydrophones.
Open Access
Analysis of the self-healing capability of thermoplastic elastomer capsules in a polymeric beam structure based on strain energy release behaviour during crack growth
(MDPI, 2023-08-12) Almutairi, Mohammed Dukhi; He, Feiyang; Alshammari, Yousef Lafi; Alnahdi, Sultan Saleh; Khan, Muhammad Ali
The objective of this study was to investigate the elastic and plastic responses of 3D-printed thermoplastic elastomer (TPE) beams under various bending loads. The study also aimed to develop a self-healing mechanism using origami TPE capsules embedded within an ABS structure. These cross-shaped capsules have the ability to be either folded or elastically deformed. When a crack occurs in the ABS structure, the strain is released, causing the TPE capsule to unfold along the crack direction, thereby enhancing the crack resistance of the ABS structure. The enhanced ability to resist cracks was confirmed through a delamination test on a double cantilever specimen subjected to quasi-static load conditions. Consistent test outcomes highlighted how the self-healing process influenced the development of structural cracks. These results indicate that the suggested self-healing mechanism has the potential to be a unique addition to current methods, which mostly rely on external healing agents.
Open Access
Analytical review of cybersecurity for embedded systems
(IEEE, 2020-12-21) Aloseel, Abdulmohsan; He, Hongmei; Shaw, Carl; Khan, Muhammad Ali
To identify the key factors and create the landscape of cybersecurity for embedded systems (CSES), an analytical review of the existing research on CSES has been conducted. The common properties of embedded systems, such as mobility, small size, low cost, independence, and limited power consumption when compared to traditional computer systems, have caused many challenges in CSES. The conflict between cybersecurity requirements and the computing capabilities of embedded systems makes it critical to implement sophisticated security countermeasures against cyber-attacks in an embedded system with limited resources, without draining those resources. In this study, twelve factors influencing CSES have been identified: (1) the components; (2) the characteristics; (3) the implementation; (4) the technical domain; (5) the security requirements; (6) the security problems; (7) the connectivity protocols; (8) the attack surfaces; (9) the impact of the cyber-attacks; (10) the security challenges of the ESs; (11) the security solutions; and (12) the players (manufacturers, legislators, operators, and users). A Multiple Layers Feedback Framework of Embedded System Cybersecurity (MuLFESC) with nine layers of protection is proposed, with new metrics of risk assessment. This will enable cybersecurity practitioners to conduct an assessment of their systems with regard to twelve identified cybersecurity aspects. In MuLFESC, the feedback from the system-components layer to the system-operations layer could help implement ‘‘Security by Design’’ in the design stage at the bottom layer. The study provides a clear landscape of CSES and, therefore, could help to find better comprehensive solutions for CSES.
Open Access
Dynamic response of 3d-printed acrylonitrile butadiene styrene (abs) damaged structure under thermo-mechanical loads.
(Cranfield University, 2021-09) He, Feiyang; Starr, Andrew; Khan, Muhammad Ali
Fused deposition modelling (FDM), as the most widely used additive manufacturing (AM) process, has great potential for various applications. The structures manufactured with the FDM technique has the potential to be used in a variety of complex working environments, such as the coupled thermo- mechanical loads. The coupled thermo-mechanical loads can likely lead to fatigue cracking swiftly in structures till the catastrophic failure. Therefore, it is critical to research the fatigue crack behaviour in FDM structures. This behaviour is mainly responsible for the change of structural stiffness and hence can influence the dynamic response of the structure under the mentioned loads. The measurement of the structural dynamic response can give us an idea of the severity due to crack growth in an in-situ manner. This thesis mainly aims to investigate the dynamic response of the cracked FDM structures under thermo- mechanical loads. The relationship between the coupled loads, crack propagation and dynamic response is developed analytically and later validated experimentally. This research has improved the existing torsional spring model, which can represent the crack depth more accurately and hence estimated the fundamental frequency of the selected structure with an up to around 20% to 120% reduced error in the case of deep cracks. Furthermore, the analytical relationship between the structural displacement amplitude and crack depth and location was modelled for the very first time in the presence of the crack breathing effect. Extensive experimentation is performed to validate the developed analytical relationship and its related theory. The fatigue crack growth of FDM ABS beams under thermo-mechanical loads with varying printing parameters is also investigated. The optimal printing parameters combination (X raster orientaion, 0.8 mm nozzle size, 0.15 mm layer thickness) is determined. The underlying reasons behind the experimental data are analysed. The outcome of this optimisation can help manufacturers to print long-life and crack resistant printed structures.
Open Access
Effect of carbon fiber winding layer on torsional characteristics of filament wound composite shafts
(Springer Verlag, 2018-03-21) Tariq, Mateen; Nisar, Salman; Shah, Aqueel; Mairaj, Tariq; Akbar, Sohaib; Khan, Muhammad Ali; Khan, Sohaib Zia
Composite materials are promising candidates as structural materials and substituting metals in extensive applications. Shafts are used in aerospace and automotive structures and hence replacing conventional shafts with composite material shafts is a viable option. Hollow shafts can be manufactured using filament winding technology employing hoop and helix winding layers. Filament winding technology offers several advantages such as continuous filaments through structure and capability for continuous manufacturing. Previously researchers have investigated composite shafts; however, this research elaborates the significance of type of winding layer on torsional characteristics. This paper reports the effects of carbon fiber winding layer on torsional characteristics of filament wound composite hollow shafts. Shafts were manufactured using filament winding technology with continuous carbon fiber roving and epoxy matrix material and tested using the torsional testing machine. The finite element (FE) simulations have been carried out with a general purpose commercial FE code, ABAQUS, to demonstrate shafts in torsional loading. The results revealed that values from torsional test correlate with developed finite element model. It was concluded that helix winding layer offers high hardness and more resistance to torsional forces as compared to hoop winding layer in filament wound composite shafts.
Open Access
Effect of hybrid reinforcement on the performance of filament wound hollow shaft
(Elsevier, 2017-09-06) Tariq, Mateen; Nisar, Salman; Shah, Aqueel; Akbar, Sohaib; Khan, Muhammad Ali; Khan, Sohaib Zia
Previous studies have shown that composite materials can replace metals as the material of construction in shafts. Composite material shafts are normally made up of polymer matrix composites as they are easy to design and economical to manufacture. This paper investigates the effect of hybrid reinforcement on the performance of filament wound hollow shaft. The hybrid shafts are composed of hybrid filaments including a combination of carbon, glass and aramid fibers. The initial stage involved development and verification of FEA model in order to establish grounds for further experimentation. Afterwards, a design of experiments model was established and experiments were performed using FEA. After the design phase, the shafts were manufactured using filament winding processing technique employing suitable matrix and reinforcement systems. Lastly, the shafts were tested for torsional characteristics, hardness, density and chemical reactivity. The results showed that carbon fiber reinforcement shows best results in terms of torsional characteristics. In terms of chemical reactivity, carbon-glass hybrid reinforcement exhibited minimum degradation. Furthermore, it was also found that hybrid reinforcements containing carbon-aramid fibers showed better results in terms of density and surface hardness.
Open Access
Experimental and numerical study of the effect of silica filler on the tensile strength of a 3D-printed particulate nanocomposite
(Elsevier, 2019-09-03) Asif, Muhammad Usman; Ramezani, Maziar; Khan, Kamran Ahmed; Khan, Muhammad Ali; Aw, Kean Chin
Polymers are commonly found to have low mechanical properties, e.g., low stiffness and low strength. To improve the mechanical properties of polymers, various types of fillers have been added. These fillers can be either micro- or nano-sized; however; nano-sized fillers are found to be more efficient in improving the mechanical properties than micro-sized fillers. In this research, we have analysed the mechanical behaviour of silica reinforced nanocomposites printed by using a new 5-axis photopolymer extrusion 3D printing technique. The printer has 3 translational axes and 2 rotational axes, which enables it to print free-standing objects. Since this is a new technique and in order to characterise the mechanical properties of the nanocomposites manufactured using this new technique, we carried out experimental and numerical analyses. We added a nano-sized silica filler to enhance the properties of a 3D printed photopolymer. Different concentrations of the filler were added and their effects on mechanical properties were studied by conducting uniaxial tensile tests. We observed an improvement in mechanical properties following the addition of the nano-sized filler. In order to observe the tensile strength, dog-bone samples using a new photopolymer extrusion printing technique were prepared. A viscoelastic model was developed and stress relaxation tests were conducted on the photopolymer in order to calibrate the viscoelastic parameters. The developed computational model of nano reinforced polymer composite takes into account the nanostructure and the dispersion of the nanoparticles. Hyper and viscoelastic phenomena was considered to validate and analyse the stress–strain relationship in the cases of filler concentrations of 8%, 9%, and 10%. In order to represent the nanostructure, a 3D representative volume element (RVE) was utilized and subsequent simulations were run in the commercial finite element package ABAQUS. The results acquired in this study could lead to a better understanding of the mechanical characteristics of the nanoparticle reinforced composite, manufactured using a new photopolymer extrusion 5-axis 3D printing technique.
Open Access
Fracture life estimation of Al-1050 thin beams using empirical data and a numerical approach
(British Institute of Non-destructive Testing, 2018-07-01) Khan, Muhammad Ali; Khan, Kamran Ahmed; Nisar, Salman; Starr, Andrew
A technique based on empirical data and finite element (FE) analysis to predict the fracture life of Al-1050 beams with the help of its fundamental mode is presented in this study. Experiments were performed on a non-prismatic beam vibrating with a constant value of the amplitude at the fixed end until the complete fracture of the specimen was achieved. The beam was vibrating at its fundamental mode to achieve fracture in less time. A power law model was used to acquire the possible trends between the values of natural frequencies and the number of cycles recorded during these experiments. These trends were further compared with a numerically modelled specimen but with artificial cracks. FE modal analysis was used for this comparison. An error of less than 1% was observed in the estimated number of total cycles obtained through the power law model before fracture, compared to those obtained using the numerical approach. Using this approach, the fracture life was also predicted for specimens of different lengths.
Open Access
Gear misalignment diagnosis using statistical features of vibration and airborne sound spectrums
(Elsevier, 2019-05-31) Khan, Muhammad Ali; Shahid, Muhammad Atayyab; Ahmed, Syed Adil; Khan, Sohaib Zia; Khan, Kamran Ahmed; Ali, Syed Asad; Tariq, Muhammad
Failure in gears, transmission shafts and drivetrains is very critical in machineries such as aircrafts and helicopters. Real time condition monitoring of these components, using predictive maintenance techniques is hence a proactive task. For effective power transmission and maximum service life, gears are required to remain in prefect alignment but this task is just beyond the bounds of possibility. These components are flexible, thus even if perfect alignment is achieved, random dynamic forces can cause shafts to bend causing gear misalignments. This paper investigates the change in energy levels and statistical parameters including Kurtosis and Skewness of gear mesh vibration and airborne sound signals when subjected to lateral and angular shaft misalignments. Novel regression models are proposed after validation that can be used to predict the degree and type of shaft misalignment, provided the relative change in signal RMS from an aligned condition to any misaligned condition is known.
Open Access
Investigation of the strain-rate-dependent mechanical behavior of a photopolymer matrix composite with fumed nano-silica filler
(Wiley, 2019-06-21) Asif, Muhammad; Ramezani, Maziar; Khan, Kamran Ahmed; Khan, Muhammad Ali; Aw, Kean Chin
With the evolution of additive manufacturing, there is an increasing demand to produce high strength and stiffness polymers. Photopolymers are very commonly used in stereolithography and fused deposition modeling processes, but their application is limited due to their low strength and stiffness values. Nano‐sized fibers or particles are generally embedded in the polymer matrix to enhance their properties. In this study, we have studied the effect of fumed nano‐sized silica filler on the elastic and viscoelastic properties of the photopolymer. The uniaxial testing coupons with different concentrations of silica filler have been fabricated via casting. We observed improvement in mechanical properties by the addition of the nano‐sized filler. As polymers exhibit time‐dependent mechanical response, we have conducted tensile tests at different strain rates as it is one of the most common modes of deformation, and is commonly used to characterize the parameters of the rate‐dependent material. We noticed significant dependence of the mechanical properties on the strain rate. quasi‐linear viscoelastic (QLV) model, which combines hyperelastic and viscoelastic phenomena, has been employed to capture the response of the material at different strain rates. We found out that the QLV model with Yeoh strain energy density function adequately describes the rate‐dependent behavior of the material and has reasonable agreement with the experimental results.
Open Access
Micromechanical modeling of architected piezoelectric foam with simplified boundary conditions for hydrophone applications
(SAGE, 2021-01-05) Khan, Kamran Ahmed; Alarafati, Hamad K.; Khan, Muhammad Ali
Architected piezoelectric materials with controlled porosity are of interest for applications such as hydrophones, miniature accelerometers, vibratory sensors, and contact microphones. Current analytical modeling approach cannot be readily applied to design architected periodic piezoelectric foams with tunable properties while exhibiting elastic anisotropy and piezoelectric activity. This study presents micromechanical-finite element (FE) models to characterize the electromechanical properties of architected piezoelectric foams. The microstructure with zero-dimension (3-0 foam, spherical porosity) and one-dimensional (3-1 foam, cylindrical porosity) connectivity were considered to analyze the effect of porosity connectivity on the performance of piezoelectric foam. 3D FE models of the 3-0 and 3-1 foams were developed and using the intrinsic symmetry of porous structures simplified mixed boundary conditions (MBCs) equivalent to periodic boundary conditions (PBC) were proposed. The proposed approach is simple and eliminates the need of tedious mesh generation process on opposite boundary faces on the micromechanical model of porous microstructures with PBCs. The results obtained from the proposed micromechanics-FE models were compared with those obtained by means of the analytical models based on micromechanics theories, and FE models with PBCs reported in the literature for both 3-0 and 3-1 type foams. An excellent agreement was observed. The computed effective elastic, piezoelectric and dielectric properties and corresponding figure of merit (FOM) revealed that piezoelectric foams with 3-0 connectivity exhibit enhanced hydrostatic FOM as compared to piezoelectric foams with 3-1 connectivity. It is concluded that spherical porosity is more suitable to hydrophone applications.
Open Access
A novel twofold symmetry architected metamaterials with high compressibility and negative Poisson's ratio
(Wiley, 2021-02-28) Khan, Kamran Ahmed; Alshaer, Mohammad H.; Khan, Muhammad Ali
This study presents the compression response of additively manufactured novel soft porous structures with architected microstructure. Six porous additively manufactured architected periodic structures with two‐fold and four‐fold symmetry were considered. The effect of pore shape and fold symmetry of microstructure on the non‐linear response of a square array of architected pores in a soft polymeric matrix is experimentally investigated. The digital image correlation (DIC) is used for investigating the evolution of strains and deformation during uniaxial tensile tests and compression tests of porous structures. Compression induced instability lead to negative Poisson's ratio, and compaction of porous structures, which is found to depend not only on the shape of the architecture but also the fold symmetry exists in the microstructure's unit cell. Unique architectures with multiple buckling modes and shape transformation are also observed. Two‐fold symmetry structures are found to buckle at lower strains compared to the four‐fold symmetric structure at the same porosity level and produced high compaction and negative Poisson's ratio. The results showed that in addition to pore shape, the fold symmetry could be used effectively to design a new class of soft, active, and reconfigurable devices over a wide range of length scales with desired characteristics.
Open Access
Physics-based modelling of cyclic deformation and microstructure-sensitive fatigue crack propagation from shallow scribes
(Cranfield University, 2020-12) Ashraf, Farhan; Castelluccio, Gustavo M.; Khan, Muhammad Ali
Face-centered cubic (FCC) metals with low to medium stacking fault energy (SFE) develop similar mesoscale substructures under cyclic loading. The formation of these substructures is controlled by dislocation interactions and loading conditions. For instance, cross slip facilitates cell formation and Hirth locks define the labyrinth structure. In the case of aluminium (high SFE metal), cross slip is easily activated and a cell structure is often observed. However, it is not always recognised that aluminium can also form PSBs at low temperatures. This highlights that the underlying mechanism controlling the cyclic response in aluminium is not different from other FCC metals. This work proposes the role of mesoscale substructure as a material-invariant among FCC metals to predict the cyclic response of aluminium. The effect of number of cycles on modelling dislocation substructures is explored, which is found to trigger a change in dislocation structures in aluminium at 298K. A crystal plasticity framework based on mesoscale substructures is developed to study the cyclic response of aluminium under different crystal orientations, strain amplitudes, number of cycles, and temperatures. Finally, this work implemented the crystal plasticity model to study the microstructure-sensitive crack propagation from shallow scribes in pure aluminium. The gradient of fatigue indicator parameters (FIPs) is estimated as crack extends inside a grain with explicit microstructure simulations, which followed the same decaying trend predicted by experiments. Thereby, an engineering solution is proposed to couple microstructural and geometric gradients at the crack tip independently. The model predicted the transgranular fatigue life with independently coupled gradients that agree well with experiments.
Open Access
Predicting the effect of voids on mechanical properties of woven composites
(IOP, 2018-09-21) Choudhry, R. S.; Sharif, Tahir; Khan, Kamran Ahmed; Khan, Sohaib Z.; Hassan, Abid; Khan, Muhammad Ali
An accurate yet easy to use methodology for determining the effective mechanical properties of woven fabric reinforced composites is presented. The approach involves generating a representative unit cell geometry based on randomly selected 2D orthogonal slices from a 3D X-ray micro-tomographic scan. Thereafter, the finite element mesh is generated from this geometry. Analytical and statistical micromechanics equations are then used to calculate effective input material properties for the yarn and resin regions within the FE mesh. These analytical expressions account for the effect of resin volume fraction within the yarn (due to infiltration during curing) as well as the presence of voids within the composite. The unit cell model is then used to evaluate the effective properties of the composite.
Open Access
A projected finite element update method for inverse identification of material constitutive parameters in transversely isotropic laminates
(Springer, 2017-03-09) Siddiqui, Muhammad Zeeshan; Khan, Sohaib Zia; Khan, Muhammad Ali; Khan, Kamran Ahmed; Shahzad, Majid; Nisar, Salman; Noman, Danish
In this paper, a novel application of Finite Element Update Method (FEUM) is proposed for the inverse identification of material constitutive parameters in transversely isotropic laminates. Two-dimensional Digital Image Correlation (2D–DIC) is used for full-field measurements which is required for the identification process. Instead of measuring the in-plane displacements, which is a well-known application of 2D–DIC, we seek to measure the pseudo-displacements resulting from out-of-plane (towards camera) deflection of plate under a point load. These pseudo-displacements are basically the perspective projection of the three dimensional displacement fields on the image-plane of the image acquisition system. The cost function in this method is defined in terms of these projections instead of the true displacements – and hence the name Projected Finite Element Update Method (PFEUM). In this article, identification of in-plane elastic moduli of Carbon Fiber Reinforced Plastic (CFRP) plate has been performed using plate bending experiments which show pre-dominantly out-of-plane deflection with little contribution from the in-plane displacements. Identification results are validated by direct experimental measurements of the unknown elastic constants as well as theoretical estimates based on volume ratio of constituents. The results show good conformance between estimated and target values for at least three material parameters namely E1, E2 and G12. Effects of experimental noise on parameter estimates has also been evaluated to explain the observed deviation in estimated parameters with current test configuration.
Open Access
Realizing surface amphiphobicity using 3D printing techniques: A critical move towards manufacturing low-cost reentrant geometries
(Elsevier, 2021-01-06) Shams, Hamza; Basit, Kanza; Khan, Muhammad Ali; Saleem, Sajid; Mansoor, Asif
Amphiphobic surfaces are obtained by lowering the surface energy through changes in surface geometry. These changes can be designed on the surface, thereby altering its wettability, and in turn rendering it amphiphobic. The main geometrical entities behind this phenomenon are reentrant geometries which prevent the solid-liquid interface tension from breaking, thereby resulting in contact angles greater than 90°. The science behind modelling and manufacturing of these reentrant geometries is well established apart from manufacturing them via extrusion-based 3-Dimensional printing processes. This review paper in identifying this gap summarizes various characterization parameters for surface wettability followed by identifying the role of surface reentrant geometries to introduce superamphiphobicity in polymers. The focus of the paper then moves towards achieving amphiphobicity using 3D printing processes where the current state of research is discussed in terms of reentrant profiles and achievement of high static contact angles. Role of the most common yet rarely reported Fused Deposition Modelling technique is discussed in more detail and a preliminary investigation based on characteristics flow and printing parameters used in Fused Deposition Modelling has been presented. The surface amphiphobicity is achieved in a one-step process characterized by high static contact angles with low and high surface tension liquids owing to air entrapment in characteristic layer-by-layer deposition features obtained in Fused Deposition Modelling.
Open Access
Revitalization of the embroidery industry using advanced technology in Saudi Arabia
(Cranfield University, 2020-02) Algamdy, Hind Mosfeer; Khan, Muhammad Ali; Aria, Indrat
The purpose of this study was to revitalize the traditional embroidery industry of the Hejaz region of the Kingdom of Saudi Arabia (KSA) by evaluating the possibility of using advanced technology, such as three-dimensional printing (3DP), in its manufacturing process. A mixed method methodology underpins this research in terms of collecting, processing and testing the data. An initial literature review revealed that factors such as an inability to meet current fashion trends, threats from global brands, lack of support from government and insufficient consumer interest are key challenges facing the traditional embroidery industry. Further qualitative evaluation pinpointed a lack of development in the manufacturing techniques of traditional embroidered clothing in the KSA as a key threat. An evaluation of existing technologies revealed that embroidery sewing machines attached to computer-aided design (CAD) software is the technology currently in use in the industry. However, due to inflexibility in adjusting to the demands of customization, it has not been able to mark any significant change. To this end, the current study proposed the use of the 3DP technique in the manufacturing process of traditional embroidered clothing but found that although 3DP has been used in the fashion industry, its use has been questioned because of wearability and quality concerns. An evaluation of responses collected from 16 manufacturers attending the Souq Okaz Festival in the city of Taif, along with 45 responses from customers of traditional embroidered clothing in three different universities in the KSA, found that both sets of stakeholders showed concerns regarding the wearability of 3DP garments. The manufacturers also shared their concerns regarding the ease of use of the technology. As a backdrop to these findings, two experiments were conducted: a washing test and a peel tensile test. The washing test revealed that 3DP embroidery designed and printed on silk, cotton and organza showed no impact from washing upon their brightness, roughness, shape or edge. However, the peel test revealed that, due to its irregular texture and shape, organza showed inconsistent adhesion of 3DP material comparative to cotton and silk. This led to the conclusion that 3DP embroidery objects present good long-term wearability, as long as the printing parameters are set up to meet the fabric architecture. Suitability, acceptability and feasibility in relation to the financial, human resource (ease of use) and supply chain aspects of 3DP embroidery clothing were also substantiated.
Open Access
Scalable wear resistant 3D printed slippery liquid infused porous surfaces (SLIPS)
(Elsevier, 2021-10-02) Shams, Hamza; Basit, Kanza; Khan, Muhammad Ali; Mansoor, Asif; Saleem, Sajid
Surface wettability is a measure of adhesion and repulsion of liquids on a material’s surface, where surface wettability may be altered by creating a new interfacial surface between the base material and the target liquid on top. Where the interface comprises of a liquid that is locked in the pores or ridges of the base material, it is then termed as liquid infused surface (LIS). LIS alters the wettability due to the distinctive properties of the interfacial liquid which now forms the new surface. If the interfacial liquid is repellent towards polar (hydrophobic) and non-polar (oleophobic) liquids, the overall surface becomes slippery (amphiphobic) and prevents any new target liquids from adhering. This phenomenon leads to the definition of slippery liquid infused porous surfaces (SLIPS), where this term not only describes its role but also its fabrication route. Here a two-step facile method is presented to quickly transform any 3D printable polymeric material into robust SLIPS, irrespective of the wettability properties of the original polymer. The complex geometrical porosity required for locking the interfacial liquid is achieved using Fused Deposition Modelling (FDM) setup. Surface wettability characteristics of the 3D printed porous structure are then enhanced by increasing the liquid-adsorption sites where the locking of the infused interfacial (repellent) liquid takes place. The SLIPS demonstrate low rolling-off (sliding) angles with both polar and non-polar solvents of up to 2 degrees with high resistance to mechanical abrasion undergoing sliding frictional wear. The robust SLIPS as produced can be quickly scaled up using existing processes used in the laboratory.
Open Access
Simulation of blended nonlinear hydrodynamics forces using radial basis function in uniform moving frame
(Elsevier, 2020-02-01) Khalid, Muhammed S.; Nisar, Salman; Khan, Sohaib Zia; Khan, Muhammad Ali; Troesch, Armin W.
This study focuses on the development of a blended technique in moving frame which encompasses nonlinearities and real time simulation of the vital early design parameters using combined exact nonlinear and quasi-nonlinear forcing terms. Generally, a full three-dimensional problem needs to be solved for the precise forward speed correction. However, in this paper the forward speed end corrections are calculated by converting the two dimensional velocity potential into a three dimensional mathematical function using radial basis function then partial differentiation is performed with respect to the longitudinal direction. The difference between the forward speed correction used for time simulation in the blended method and the strip-theory in the frequency domain has been explained. The use of radial basis functions for the estimation of quasi-nonlinear combined radiation and diffraction pressures in moving frame and their conversion between two and three dimensions has been demonstrated and validated experimentally.
Open Access
Structural dynamics and crack propagation behaviour under uniform and non-uniform temperature conditions.
(Cranfield University, 2022-02) Kamei, Khangamlung; Khan, Muhammad Ali; Starr, Andrew
The robustness and stability of machinery depend on structural integrity. This stability is, however, compromised by aging, wear and tear, overloads, and environmental factors. A study of vibration and fatigue crack growth for structural health monitoring is one of the core research areas in recent times. The research is yet to input sufficient explanations about the dynamic behaviour of the structure under distributed temperature. The structural dynamics can be influenced by material microstructure, temperature distribution, and duration of exposure to the thermal environment. The applied temperature can cause significant variations in the modal response. The existing studies are limited concerning temperature change and compel extensive investigation in a crack and uncracked condition. In this research, the structural dynamics and fatigue crack propagation behaviour when subjected to thermal and mechanical loads have been studied. It investigates the modal parameters of uncracked and various cracked specimens under uniform and non-uniform temperature conditions. An analytical model considering the effective length of the beam is developed to analyse the modal response of the beam. Then, the model is modified to enumerate the modal behaviour of the beam in the presence of crack. The model is validated by experimental and numerical approaches. The experimental evaluation is conducted by considering three heating rates to attain the required temperatures. In the first case, ramping at 2°C/min is assumed as a slow heating rate. While ramping at 5°C/min and 8°C/min are assumed as moderate and rapid heating rates respectively. The heating rates are considered to compare the structural response changes. A small variation on modal parameters is noticed for different heating rates and when the applied uniform temperatures are changed to non-uniform temperatures, especially at elevated temperatures. This signifies heating at different rates has a slight effect while measuring the dynamic response of any mechanical system. The results showed that changes in modal parameters of the beam are associated with the change in temperatures and heating rate. Furthermore, this research substantiates the fatigue crack propagation behaviour of pre-seeded cracks. The propagated crack depths are measured based on pixels contains in the crack. It is found that propagated crack depends on applied temperatures and associated mass. The appearance of double crack fronts and multiple cracks are observed. The multiple crack appearance seems due to the selection of pre-seeded crack shapes. Hence, the real crack and pre- seeded crack are distinct and need careful consideration in crack propagation evaluation.