Saeid Lotfian - Academia.edu (original) (raw)

Papers by Saeid Lotfian

International Journal of Biological Macromolecules

MRS Advances, Jan 30, 2017

Advances in Materials and Processing Technologies, Dec 18, 2015

Acta Materialia, Jul 1, 2013

The effect of the temperature on the compressive stress-strain behavior of Al/SiC nanoscale multi... more The effect of the temperature on the compressive stress-strain behavior of Al/SiC nanoscale multilayers was studied by means of micropillar compression tests at 23 °C and 100 °C. The multilayers (composed of alternating layers of 60 nm in thickness of nanocrystalline A1 and amorphous SiC) showed a very large hardening rate at 23 °C, which led to a flow stress of 3.1 ± 0.2 GPa at 8% strain. However, the flow stress (and the hardening rate) was reduced by 50% at 100 °C. Plastic deformation of the A1 layers was the dominant deformation mechanism at both temperatures, but the A1 layers were extruded out of the micropillar at 100 °C, while A1 plastic flow was constrained by the SiC elastic layers at 23 °C. Finite element simulations of the micropillar compression test indicated the role played by different factors (flow stress of Al, interface strength and friction coefficient) on the mechanical behavior and were able to rationalize the differences in the stress-strain curves between 23 °C and 100 °C.

Physics of Fluids

The use of flexible materials for primary mover and power takeoff of wave energy converters (WECs... more The use of flexible materials for primary mover and power takeoff of wave energy converters (WECs) has attracted considerable attention in recent years, owing to their potential to enhance the reliability, survivability, and wave energy conversion efficiency. Although some reduced order models have been used to study the fluid–structure interaction (FSI) responses of flexible wave energy converters (fWECs), they are somehow inappropriate due to their limited accuracy and applicability span. To gain a deeper understanding of the physical mechanisms in fWECs, a high-fidelity approach is required. In this work, we build up a fluid–structure interaction analysis framework based on computational fluid dynamics and a finite element analysis method. The incompressible viscous flow is resolved by solving three-dimensional unsteady Navier–Stokes equations with a finite volume approach. The structure dynamics are solved by a finite element method, taking the nonlinear behavior of flexible mat...

Functional Composite Materials

Epoxy is widely used material, but epoxy has limitations in terms of brittleness in failure, and ... more Epoxy is widely used material, but epoxy has limitations in terms of brittleness in failure, and thus researchers explore toughening and strengthening options such as adding a second phase or using electromagnetic fields to tailor toughness and strength, on demand and nearly instantaneously. Such approach falls into the category of active toughening but has not been extensively investigated. In this research, Si-BaTiO3 nanoparticles were used to modify the electro-mechanical properties of a high-performance aerospace-grade epoxy so as to study its response to electric fields, specifically low field strengths. To promote uniform dispersion and distribution, the Si-BaTiO3 nanoparticles were functionalised with silane coupling agents and mixed in the epoxy Araldite LY1564 at different content loads (1, 5, 10 wt%), which was then associated with its curing agent Aradur 3487. Real-time measurements were conducted using Raman spectroscopy while applying electric fields to the nanocomposit...

Current Opinion in Green and Sustainable Chemistry

Epoxy is an important class of thermosetting material which have been used in many fields such as... more Epoxy is an important class of thermosetting material which have been used in many fields such as aerospace, automobile, and energy sectors. Cured epoxy, however, exhibits poor resistance to crack initiation and growth, thus exhibiting low toughness and brittleness at failure. To improve the mechanical properties, epoxy matrix in polymer composites has been modified by various techniques such as the inclusion of a second phase (e.g., core-shell rubber, thermoplastics or nanofillers) which has demonstrated improved toughness and impact resistance. Very few studies have focused on offering an ‘active toughening’ mechanism in which an increase in toughness and strength is achieved via remote field stimulation such as magnetic, electric or electromagnetic forces. In this study, aerospace grade epoxy resin modified with tetragonal barium titanate (BaTiO3) nanoparticles has been prepared, and its mechanical response has been studied under electric field stimulations. The BaTiO3 nanopartic...

Energies

The main obstacle against the penetration of wind power into the power grid is its high variabili... more The main obstacle against the penetration of wind power into the power grid is its high variability in terms of wind speed fluctuations. Accurate power forecasting, while making maintenance more efficient, leads to the profit maximisation of power traders, whether for a wind turbine or a wind farm. Machine learning (ML) models are recognised as an accurate and fast method of wind power prediction, but their accuracy depends on the selection of the correct hyperparameters. The incorrect choice of hyperparameters will make it impossible to extract the maximum performance of the ML models, which is attributed to the weakness of the forecasting models. This paper uses a novel optimisation algorithm to tune the long short-term memory (LSTM) model for short-term wind power forecasting. The proposed method improves the power prediction accuracy and accelerates the optimisation process. Historical power data of an offshore wind turbine in Scotland is utilised to validate the proposed method...

Metals

In this study, combustion synthesis involving mechanical milling and subsequent sintering process... more In this study, combustion synthesis involving mechanical milling and subsequent sintering process was utilised to fabricate Cu/AlxCuy/Al2O3 in-situ composite through the aluminothermic reduction of CuO powders. First, CuO and Al powders were mixed, and ball milled for 30–150 min to facilitate self-propagating high-temperature synthesis (SHS). Then, mechanically activated Al-CuO powders were mixed with elemental Cu powders and experienced subsequent cold compaction and sintering processes. The reactions during synthesis were studied utilising differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Densification and hardness of green and sintered bodies were also obtained. The results indicated that despite the negative free energy of the aluminothermic reaction, an initial activation energy supply is required, and mixed Al-CuO powders did not show significant progress in the combustion synthesis method. The aluminothermic reaction became ...

Fatigue & Fracture of Engineering Materials & Structures

A study has been conducted to evaluate the mechanical and fatigue crack propagation properties of... more A study has been conducted to evaluate the mechanical and fatigue crack propagation properties of wire + arc additively manufactured ER70S‐6 components. A parallel‐built deposition strategy was employed to fabricate the additively manufactured wall. The hardness values were slightly higher at the bottom and top of the wall due to the presence of Widmanstätten ferrite and carbides. The characterization of mechanical properties in both orientations; parallel and perpendicular to the deposition direction showed a marginal difference in yield strength and ultimate tensile strength. The crack growth rates were correlated with linear elastic fracture mechanics parameter ΔK and compared with an oscillation‐built deposition strategy from the literature. The crack growth rates of both deposition strategies were found to be very similar to each other. Furthermore, it has been demonstrated that the variability in the crack growth histories can be reasonably well captured by using the NASGRO cr...

Metals, 2021

Progress in sustainable manufacturing is a crucial element to minimise negative environmental imp... more Progress in sustainable manufacturing is a crucial element to minimise negative environmental impacts. The conventional fusion weld process used to join aluminium alloys resulted in coarse grain structure, inevitable defects, and severe joint softening. Friction stir processing (FSP) has the potential to modify the microstructure of materials in joint structure and improve the mechanical properties. In this investigation, the effect of friction stir post–processing was evaluated to study the microstructural characteristics and mechanical properties of GTAW (gas tungsten arc welding) welds in the aluminium 5052 alloy. During FSP, the grains’ dendritic microstructure was destroyed, and the dynamic recrystallisation resulted in a very fine and equiaxed grains structure in the fusion zone. The hardness of the friction-stir-processed welds significantly improved because of microstructure grain refinement. The processed joint demonstrated higher ultimate tensile and yield strength (~275 M...

Gels, 2022

Bone marrow-derived mesenchymal stem cells (MSCs) offer a promising therapeutic method for cardia... more Bone marrow-derived mesenchymal stem cells (MSCs) offer a promising therapeutic method for cardiac tissue regeneration. However, to monitor the fate of MSCs for tissue repair, a better stem cell delivery carrier is needed. Developing a unique injectable and shear-thinning dual cross-linked hybrid hydrogel for MSC delivery for cardiac tissue engineering is highly desirable. This hydrogel was synthesised using guest: host reaction based on alginate-cyclodextrin (Alg-CD) and adamantane-graphene oxide (Ad-GO). Here, the role of macromere concentration (10 and 12%) on the MSC function is discussed. Our hybrid hydrogels reveal a suitable oxygen pathway required for cell survival. However, this value is strongly dependent on the macromere concentrations, while the hydrogels with 12% macromere concentration (2DC12) significantly enhanced the oxygen permeability value (1.16-fold). Moreover, after two weeks of culture, rat MSCs (rMSCs) encapsulated in Alg-GO hydrogels expressed troponin T (TN...

Raw data and calculation of Mode-I fracture toughness at initiation and propagation for different... more Raw data and calculation of Mode-I fracture toughness at initiation and propagation for different densities of electrospun nanofibres embedded for toughening of composite laminates

The paper shows that the suitable addition of carbon nanomaterials to a tin-based solder material... more The paper shows that the suitable addition of carbon nanomaterials to a tin-based solder material matrix results in two fold strength of soldered joints.<br><br><br>

Emergent Materials, 2021

Weight reduction and improved strength are two common engineering goals in the joining sector to ... more Weight reduction and improved strength are two common engineering goals in the joining sector to benefit transport, aerospace, and nuclear industries amongst others. Here, in this paper, we show that the suitable addition of carbon nanomaterials to a tin-based solder material matrix (C-Solder® supplied by Cametics Ltd.) results in two-fold strength of soldered composite joints. Single-lap shear joint experiments were conducted on soldered aluminium alloy (6082 T6) substrates. The soldering material was reinforced in different mix ratios by carbon black, graphene, and single-walled carbon nanotubes (SWCNT) and benchmarked against the pristine C-solder®. The material characterisation was performed using Vickers micro-indentation, differential scanning calorimetry and nano-indentation, whereas functional testing involved mechanical shear tests using single-lap aluminium soldered joints and creep tests. The hardness was observed to improve in all cases except for the 0.01 wt.% graphene ...