Modelling the Flow Behaviour of Al Alloy Sheets at Elevated Temperatures Using a Modified Zerilli-Armstrong Model and Phenomenological-Based Constitutive Models.

The flow behaviour of AA2060 Al alloy under warm/hot deformation conditions is complicated because of its dependency on strain rates (ε˙), strain (ε), and deformation modes. Thus, it is crucial to reveal and predict the flow behaviours of this alloy at a wide range of temperatures (T) and ε˙ using different constitutive models. Firstly, the isothermal tensile tests were carried out via a Gleeble-3800 thermomechanical simulator at a T range of 100, 200, 300, 400, and 500 °C and ε˙ range of 0.01, 0.1, 1, and 10 s-1 to reveal the warm/hot flow behaviours of AA2060 alloy sheet. Consequently, three phenomenological-based constitutive models (L-MJC, S1-MJC, S2-MJC) and a modified Zerilli-Armstrong (MZA) model representing physically based constitutive models were developed to precisely predict the flow behaviour of AA2060 alloy sheet under a wide range of T and ε˙. The predictability of the developed constitutive models was assessed and compared using various statistical parameters, including the correlation coefficient (R), average absolute relative error (AARE), and root mean square error (RMSE). By comparing the results determined from these models and those obtained from experimentations, and confirmed by R, AARE, and RMSE values, it is concluded that the predicted stresses determined from the S2-MJC model align closely with the experimental stresses, demonstrating a remarkable fit compared to the S1-MJC, L-MJC, and MZA models. This is because of the linking impact between softening, the strain rate, and strain hardening in the S2-MJC model. It is widely known that the dislocation process is affected by softening and strain rates. This is attributed to the interactions that occurred between ε and ε˙ from one side and between ε, ε˙, and T from the other side using an extensive set of constants correlating the constitutive components of dynamic recovery and softening mechanisms.

Biocomposites of Poly(Lactic Acid) and Microcrystalline Cellulose: Influence of the Coupling Agent on Thermomechanical and Absorption Characteristics.

In this study, poly(lactic acid) (PLA) and microcrystalline cellulose (MCC)-based green biocomposites were developed using a solution casting technique. Essentially, the bonding between PLA and MCC is quite feeble; therefore, the current study is conducted to strengthen the bonding by incorporating a coupling agent, thereby enhancing the overall quality of the biocomposites. Thus, the present study aimed to examine the influence of combined coupling agents-maleic anhydride (MAH) and maleic acid (MA) (MAH-MA)-on the properties of polylactic acid (PLA)/microcrystalline cellulose (MCC) biocomposites. The investigation also encompassed an examination of the impact of MCC loading (2, 3, and 5% w/w) into a PLA matrix. The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) examination revealed the interfacial interaction and adhesion among MCC, PLA, and coupling agents and the formation of biocomposites. The incorporation of MAH-MA led to improved mechanical properties of the PLA/MCC biocomposites. Furthermore, the incorporation of MAH-MA into the PLA/3 wt % MCC composite exhibited enhancements in both the tensile strength and tensile modulus, accompanied by a reduced elongation at break. In addition, it is worth noting that the thermogravimetric analysis (TGA) curve of the PLA composite with 3% w/w of MCC and MAH-MA displayed a significant decrease in weight beyond a temperature threshold of 492.65 °C. The water absorption demonstrates that the incorporation of MAH-MA into the PLA/MCC composite led to advantageous water barrier characteristics. The observed improvements were attributed to the efficient dispersion of MCC at the most favorable amount of coupling agents, along with the chemical interactions involving grafting and esterification between MCC and the MAH-MA coupling agent. Furthermore, the incorporation of MAH-MA into the PLA/3% (w/w) MCC composite exhibited enhancements in both the tensile strength and tensile modulus, accompanied by a reduction in the elongation percentage at break. The experimental results about water absorption demonstrate that the incorporation of MAH-MA into the PLA/MCC composite led to advantageous water barrier characteristics. These improvements were attributed to good MCC dispersion and the chemical interactions involving grafting and esterification between the MCC and the MAH-MA coupling agent.

Modeling and Experimental Investigation of U-R Relationship of AA6061-T6 Tubes Manufactured via Free Bending Forming Process.

Forming tubes with various bending radii without changing the bending dies is much easier for the 3D free bending forming (FBF) process. In the 3D-FBF process, different bending radii were realized by adapting the eccentricities of the bending dies. The accuracy of the U-R curve is crucial for the precision forming of complex bending components. In this study, the U-R relation curve of the Al alloy tube with a specific friction coefficient, fixed geometry size, clearance between tubes, and bending die was fitted first based on the forming results of AA6061-T6 tubes under different eccentricities. Second, the U-R relationship curve based on the experiment is used to propose the U-R relationship's mathematical formula based on many hypotheses. Finally, the modified U-R mathematical formula was applied in the finite element (FE) simulation and the actual FBF experiments for the AA6061-T6 Al alloy complex shape space bending members. The U-R relationship curve's reliability was verified by comparing the simulation and experimental results. The results obtained from the modified U-R relationship align well with the FE modeling results and can be directly applied to the bending process for the intended components.

Coupling Computational Homogenization with Crystal Plasticity Modelling for Predicting the Warm Deformation Behaviour of AA2060-T8 Al-Li Alloy.

This study aimed to propose a new approach for predicting the warm deformation behaviour of AA2060-T8 sheets by coupling computational homogenization (CH) with crystal plasticity (CP) modeling. Firstly, to reveal the warm deformation behaviour of the AA2060-T8 sheet, isothermal warm tensile testing was accomplished using a Gleeble-3800 thermomechanical simulator at the temperatures and strain rates that varied from 373 to 573 K and 0.001 to 0.1 s-1. Then, a novel crystal plasticity model was proposed for describing the grains' behaviour and reflecting the crystals' actual deformation mechanism under warm forming conditions. Afterward, to clarify the in-grain deformation and link the mechanical behaviour of AA2060-T8 with its microstructural state, RVE elements were created to represent the microstructure of AA2060-T8, where several finite elements discretized every grain. A remarkable accordance was observed between the predicted results and their experimental counterparts for all testing conditions. This signifies that coupling CH with CP modelling can successfully determine the warm deformation behaviour of AA2060-T8 (polycrystalline metals) under different working conditions.

Finite Element Analysis and Experimental Study of Manufacturing Thin-Walled Five-Branched AISI 304 Stainless Steel Tubes with Different Diameters Using a Hydroforming Process.

This study aims to investigate the feasibility of hydroforming (HF) technology coupled with response surface optimization for producing high-quality five-branched AISI 304 stainless steel tubes with different diameters, addressing the shortcomings of traditional manufacturing processes. Conventional techniques often result in issues with multiple consumables, low precision, and subpar performance. The research focuses on finding optimal forming parameters for a more effective process. Initial attempts at a five-branched tube proved unfeasible. Instead, a multi-step forming approach was adopted, starting with the formation of the upper branch tube followed by the two reducing lower branch tubes, a strategy termed "first three, then five". This method, enhanced by a subsequent solid solution treatment, yielded promising results: the combined height of the upper and lower branches was 141.1 mm, with a maximum thinning rate of 26.67%, reduced to 25.33% after trimming. These outcomes met the product usage requirements. Additionally, the study involved designing and developing dies for manufacturing five-branched tubes with different diameters using servo HF equipment. The effectiveness of the multi-step forming process and parameter combinations was confirmed through experimental validation, aligning closely with the FE simulation results. The maximum thinning rate observed in the experiments was 27.60%, indicating that FE simulation and response surface methodology can effectively guide the production of high-quality parts with superior performance.

Fabrication and Thermo-Electro and Mechanical Properties Evaluation of Helical Multiwall Carbon Nanotube-Carbon Fiber/Epoxy Composite Laminates.

The development of advanced composite materials has taken center stage because of its advantages over traditional materials. Recently, carbon-based advanced additives have shown promising results in the development of advanced polymer composites. The inter- and intra-laminar fracture toughness in modes I and II, along with the thermal and electrical conductivities, were investigated. The HMWCNTs/epoxy composite was prepared using a multi-dispersion method, followed by uniform coating at the mid-layers of the CF/E prepregs interface using the spray coating technique. Analysis methods, such as double cantilever beam (DCB) and end notched flexure (ENF) tests, were carried out to study the mode I and II fracture toughness. The surface morphology of the composite was analyzed using field emission scanning electron microscopy (FESEM). The DCB test showed that the fracture toughness of the 0.2 wt.% and 0.4 wt.% HMWCNT composite laminates was improved by 39.15% and 115.05%, respectively, compared with the control sample. Furthermore, the ENF test showed that the mode II interlaminar fracture toughness for the composite laminate increased by 50.88% and 190%, respectively. The FESEM morphology results confirmed the HMWCNTs bridging at the fracture zones of the CF/E composite and the improved interlaminar fracture toughness. The thermogravimetric analysis (TGA) results demonstrated a strong intermolecular bonding between the epoxy and HMWCNTs, resulting in an improved thermal stability. Moreover, the differential scanning calorimetry (DSC) results confirmed that the addition of HMWCNT shifted the Tg to a higher temperature. An electrical conductivity study demonstrated that a higher CNT concentration in the composite laminate resulted in a higher conductivity improvement. This study confirmed that the demonstrated dispersion technique could create composite laminates with a strong interfacial bond interaction between the epoxy and HMWCNT, and thus improve their properties.

Knowledge, attitude, and practice of childbearing women toward epidural anesthesia during normal vaginal delivery in Alsanayeah Primary Health Care in Khamis Mushait.

BACKGROUND: Labor pain is a severe form of agony that females experience while giving birth. A lot of pregnant women prefer epidural anesthesia (EA) to avoid labor pain. OBJECTIVE: This study focuses on women's general awareness about EA during the childbearing age. METHODS: A cross-sectional, hospital-based study was conducted using a self-administered questionnaire. The study included all females of childbearing age getting routine antenatal care. The survey was designed to measure their awareness toward EA. A total of 328 females participated in the study. Of these, 205 (62.5%) women showed a low level of knowledge toward EA. Data were analyzed using the Chi-square test and Independent Samples t-test. RESULTS: Participants in our study included 328 women of childbearing age. Most women (172 [52.4%]) participating in the study were aged between 30 and 40 years. In terms of education, 204 (62.2%) women had university-level education. Two hundred and ninety (88.4%) women were multipara. The majority of women (205 [62.5%]) had a low-level knowledge about EA with a significant relationship between the level of perception and primary education, as well as postgraduation with P < 0.023 and P < 0.001, respectively. Also, previous EA with pregnancy significantly related to the level of knowledge with P < 0.001. Through past pregnancies, 106 (32.3%) women had experience with EA. Of these, EA caused complications in only 13 (12.3%) women and side effects in 29 (27.4%) women. CONCLUSION: The majority of women of childbearing age had limited knowledge about the benefits and complications associated with EA. During the antenatal visit, it is essential to educate all women about EA. This could be done by the obstetrician, anesthesiologist, or midwives and/or through flyers and brochures.

Properties of multifunctional composite materials based on nanomaterials: a review.

Composite materials are being used for high-end applications such as aviation technology, space ships, and heavy equipment manufacturing. The use of composite materials has been observed in recent advancements in the field of multifunctional composite materials (MFCMs). There is continuous progress related to improvements, innovations, and replacement of metals inspite of rigorous destructive and non-destructive testing, proving the toughness and lifelong durability of such materials. The present study aims to review the topics relevant to modern multifunctional composite materials. The reviewed articles mostly cover the field of MFCMs based on nanomaterials. The structural functions emphasize on the mechanical properties such as fracture toughness, strength, thermal stability, damping, stiffness, and tensile strength. The non-structural properties include biodegradability, thermal conductivity, electrical conductivity, and electromagnetic interference (EMI) shielding. The study has concluded that the applications of multifunctional nanoparticle-based composite materials and structures include durable but light-weight aircraft wings, components and structures of electric self-driving vehicles, and biomedical composite materials for drug delivery.