Influence of rGO on the Crystallization Kinetics, Cytoxicity, and Electrical and Mechanical Properties of Poly (L-lactide-co-ε-caprolactone) Scaffolds

Biodegradable scaffolds of poly (L-lactide-co-ε-caprolactone) (PLCL) and reduced graphene oxide (rGO) were prepared by TIPS (thermally induced phase separation). The nonisothermal cold crystallization kinetics were investigated by differential scanning calorimetry (DSC) with various cooling rates. The experimental values indicate that nonisothermal crystallization improves with cooling rate, but the increasing rGO concentration delays crystallization at higher temperatures. The activation energies were calculated by the Kissinger equation; the values were very similar for PLCL and for its compounds with rGO. The electrical conductivity measurements show that the addition of rGO leads to a rapid transition from insulating to conductive scaffolds with a percolation value of ≈0.4 w/w. Mechanical compression tests show that the addition of rGO improves the mechanical properties of porous substrates. In addition, it is an anisotropic material, especially at compositions of 1% w/w of rGO. All of the samples with different rGO content up to 1% are cytotoxic for C2C12 myoblast cells.This work was supported by the University of The Basque Center. The authors acknowledge funding by Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/10.13039/501100011033 and from the Basque Government Industry Departments under the ELKARTEK program. This work has been also supported by FCT–Fundação para a Ciência e Tecnologia (FCT) under the scope of the strategic funding of UID/FIS/04650/2020 and UIDB/04469/2020 units and project PTDC/BTM-MAT/28237/2017

Analysis of Wall Thickness Eccentricity in the Rotary Tube Piercing Process Using a Strain Correlated FE Model

The wall thickness eccentricity is one of the most important weaknesses that appears in seamless tubes production, since this imperfection is subsequently transferred downstream through the manufacturing stages until the final product. For this reason, in this article a finite element model of the rotary tube piercing (RTP) process is developed aimed at analysing the wall thickness eccentricity imperfection. Experimental data extracted from the industrial process is used for the validation of the model, including operational process variables like power consumption and process velocity, and deformation variables as elongation and longitudinal torsion, originated by axial and shear strain respectively. The cause of longitudinal torsion is also analysed. The two most important conclusions derived from this study are: (I) the longitudinal torsion of the tube is a crucial parameter for the correct model validation, and (II) the combined effect between the uneven temperature distribution of the billet and the plug bending deformation is identified as the major cause of the wall thickness eccentricity flaw

Application of an Incremental Constitutive Model for the FE Analysis of Material Dynamic Restoration in the Rotary Tube Piercing Process

In the numerical simulation of hot forming processes, the correct description of material flow stress is very important for the accuracy of the results. For complex manufacturing processes, such as the rotary tube piercing (RTP), constitutive laws based on both power and exponential mathematical expressions are commonly used due to its inherent simplicity, despite the limitations that this approach involves, namely, the use of accumulated strain as a state parameter. In this paper, a constitutive model of the P91 steel derived from the evolution of dislocation density with strain, which takes into account the mechanisms of dynamic recovery (DRV) and dynamic recrystallization (DRX), is proposed for the finite element (FE) analysis of the RTP process. The material model is developed in an incremental manner to allow its implementation in the FE code FORGE®. The success of this implementation is confirmed by the good correlation between results of the simulation and experimental measurements of the manufactured tube (elongation, twist angle, mean wall thickness and eccentricity). In addition, this incremental model allows addressing how the restoring mechanisms of DRV and DRV occur during the RTP process. The analysis puts into evidence that DRV and DRX prevail over each other cyclically, following an alternating sequence during the material processing, due mainly to the effect of the strain rate on the material

The effect of temperature and strain rate on the mechanical properties and microstructure of super Cr13 martensitic stainless steel

In this study, the formability of super Cr13 martensitic stainless steel (MSS) is examined by means of hot tensile tests at different temperatures (900oC-1100oC) and t strain rates (0.01s-1-10s-1). The potential effect of strain rates and temperatures on the mechanical properties, microstructure and fracture surface of super Cr13 MSS were examined. The post-test analysis, which includes hardness measurements, X-ray diffraction (XRD), fracture analysis by scanning electron microscope (SEM), and Energy-dispersive X-ray spectroscopy (EDS), was carried out. Results show that ultimate tensile stress (UTS) decreases with temperature, this way, the highest UTS was obtained at 900oC-10s-1 (187MPa), while the lowest UTS (38MPa) was obtained in the 1100oC-0.01s-1 sample. By contrast the elongation of the material increases with strain rate, since the elongation of the sample at 900oC-10s-1 was near 16% and the elongation of the sample at 1100oC-0.01s-1 was 57%. The XRD and EDS analysis indicated that Cr23C6 and Cr2N are formed inside the microstructure of samples tested between 900oC and 1000oC, and these carbides are dissolved above 1000º C. Temperature affects also retained austenite which increases with temperature. Fractography analysis indicated that the δ-ferrite phase has a primary role in high-temperature rapture. Fracture surface evaluation of samples revealed semi-ductile fracture behaviour below 1000°C and low strain rates, while ductile fracture was detected on the tensile samples at temperatures higher than 1000°C and high strain rates. Furthermore, the ductility of super Cr13 MSS was increased by increasing strain rate.Validerad;2023;Nivå 2;2023-07-20 (sofila)</p

Analysis of Friction Stir Welding Tool Offset on the Bonding and Properties of Al–Mg–Si Alloy T-Joints

Research on T-configuration aluminum constructions effectively decreases fuel consumption, increases strength, and develops aerial structures. In this research, the effects of friction stir welding (FSW) tool offset (TO) on Al–Mg–Si alloy mixing and bonding in T-configurations is studied. The process is simulated by the computational fluid dynamic (CFD) technique to better understand the material mixing flow and the bonding between the skin and flange during FSW. According to the results, the best material flow can be only achieved at an appropriate TO. The appropriate TO generates enough material to fill the joint line and results in formation of the highest participation of the flange in the stir zone (SZ) area. The results show that, in the T-configuration, FSW joints provide raw materials from the retreating side (RS) of the flange that play a primary role in producing a sound mixing flow. The selected parameters were related to the geometric limitations of the raw sheets considered in this study. The failure point of all tensile samples was located on the flange. Surface tunneling is the primary defect in these joints, which is produced at high TOs. Among the analyzed cases, the most robust joint was made at +0.2 mm TO on the advancing side (AS), resulting in more than 60% strength of the base aluminum alloy being retained

Life Cycle Assessment of a Lithium Iron Phosphate (LFP) Electric Vehicle Battery in Second Life Application Scenarios

This paper presents a life cycle assessment (LCA) study that examines a number of scenarios that complement the primary use phase of electric vehicle (EV) batteries with a secondary application in smart buildings in Spain, as a means of extending their useful life under less demanding conditions, when they no longer meet the requirements for automotive purposes. Specifically, it considers a lithium iron phosphate (LFP) battery to analyze four second life application scenarios by combining the following cases: (i) either reuse of the EV battery or manufacturing of a new battery as energy storage unit in the building; and (ii) either use of the Spanish electricity mix or energy supply by solar photovoltaic (PV) panels. Based on the Eco-indicator 99 and IPCC 2007 GWP 20a methods, the evaluation of the scenario results shows that there is significant environmental benefit from reusing the existing EV battery in the secondary application instead of manufacturing a new battery to be used for the same purpose and time frame. Moreover, the findings of this work exemplify the dependence of the results on the energy source in the smart building application, and thus highlight the importance of PVs on the reduction of the environmental impact

Influence of rGO on the cristallization kinetics, cytoxicity, electrical and mechanical properties of PLCL scaffolds

Biodegradable scaffolds of poly (L-lactide-co-ε-caprolactone) (PLCL) and reduced graphene oxide (rGO) were prepared by TIPS (thermally induced phase separation). The nonisothermal cold crystallization kinetics were investigated by differential scanning calorimetry (DSC) with various cooling rates. The experimental values indicate that nonisothermal crystallization improves with cooling rate, but the increasing rGO concentration delays crystallization at higher temperatures. The activation energies were calculated by the Kissinger equation; the values were very similar for PLCL and for its compounds with rGO. The electrical conductivity measurements show that the addition of rGO leads to a rapid transition from insulating to conductive scaffolds with a percolation value of ≈0.4 w/w. Mechanical compression tests show that the addition of rGO improves the mechanical properties of porous substrates. In addition, it is an anisotropic material, especially at compositions of 1% w/w of rGO. All of the samples with different rGO content up to 1% are cytotoxic for C2C12 myoblast cells.This work was supported by the University of The Basque Center. The authors acknowledge funding by Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/10.13039/501100011033 and from the Basque Government Industry Departments under the ELKARTEK program. This work has been also supported by FCT-Fundacao para a Ciencia e Tecnologia (FCT) under the scope of the strategic funding of UID/FIS/04650/2020 and UIDB/04469/2020 units and project PTDC/BTM-MAT/28237/2017

An Incremental Physically-Based Model of P91 Steel Flow Behaviour for the Numerical Analysis of Hot-Working Processes

This paper is aimed at modelling the flow behaviour of P91 steel at high temperature and a wide range of strain rates for constant and also variable strain-rate deformation conditions, such as those in real hot-working processes. For this purpose, an incremental physically-based model is proposed for the P91 steel flow behavior. This formulation considers the effects of dynamic recovery (DRV) and dynamic recrystallization (DRX) on the mechanical properties of the material, using only the flow stress, strain rate and temperature as state variables and not the accumulated strain. Therefore, it reproduces accurately the flow stress, work hardening and work softening not only under constant, but also under transient deformation conditions. To accomplish this study, the material is characterised experimentally by means of uniaxial compression tests, conducted at a temperature range of 900–1270 °C and at strain rates in the range of 0.005–10 s−1. Finally, the proposed model is implemented in commercial finite element (FE) software to provide evidence of the performance of the proposed formulation. The experimental compression tests are simulated using the novel model and the well-known Hansel–Spittel formulation. In conclusion, the incremental physically-based model shows accurate results when work softening is present, especially under variable strain-rate deformation conditions. Hence, the present formulation is appropriate for the simulation of the hot-working processes typically conducted at industrial scale