Construcción de curvas límite de formabilidad para aceros de bajo carbono utilizados en la manufactura de cilindros a presión

Context: The aim of this study is to determine the formability of SG295 (2,2 mm thick) and SG325 (2,3 mm thick) steel sheets, as well as their relationship with the sheets’ behavior in deep drawing and stretching operations. To this effect, chemical, metallographic, and mechanical analyses of the sheets were carried out. Method: The chemical analysis was carried out via optical emission spectrometry, and the metallographic structure was analyzed using the ASTM E3 standard. The intrinsic properties related to the formability of materials such as the elongation to fracture for a 50 mm gauge length, the conventional yield limit at 0,2% elongation, the ultimate strength, the strain hardening exponent, and the anisotropy coefficient at 15% elongation were determined through tensile tests according to ASTM E8M, ASTM E646, and ASTM 517. Forming limit curves were determined under ASTM E2218, for which a device was designed, built, and attached to a universal testing machine. Results: The results for the SG295 and SG325 steel sheets were as follows: tensile strength; 450 and 520 MPa; elongation at fracture: 24,9 and 17,2%; strain hardening exponent: 0,24 and 0,19; normal anisotropy: 1,64 and 1,29; planar anisotropy: 0,23 and -0,02. The FLD0 determined from the formality limit curves (FLCs) for the two steel sheets showed ε1 values of 0,281 and 0,336, respectively. Conclusions: Although the intrinsic properties (such as A50, n, and rm) of the SG295 steel sheet show values related to a greater formability, the FLCs show that SG325 steel performs slightly better due to its greater thickness.Contexto: El objetivo de este trabajo fue determinar la formabilidad de láminas de acero SG295 (2,2 mm de grosor) y SG325 (2,3 mm de grosor), así como su relación con el comportamiento de estas frente a operaciones de estirado y embutido profundo. Para tal fin, se realizaron análisis químicos, metalográficos y mecánicos en las láminas. Método: El análisis químico se realizó mediante espectrometría de emisión óptica, y la estructura metalográfica se analizó utilizando el estándar ASTM E3. Las propiedades intrínsecas relacionadas con la formabilidad de los materiales, tales como el alargamiento a la fractura para una longitud de referencia de 50 mm, el límite de rendimiento convencional al 0,2 % de elongación, la resistencia última, el exponente de endurecimiento por deformación y el coeficiente de anisotropía al 15 % de elongación se determinaron mediante pruebas de tracción de acuerdo con ASTM E8M, ASTM E646 y ASTM 517. Las curvas límite de formabilidad se determinaron bajo la norma ASTM E2218, para lo cual se diseñó, construyó y acopló un dispositivo a una máquina universal de ensayos. Resultados: Los resultados para las láminas de acero SG295 y SG325 fueron los siguientes: resistencia a la tracción: 450 y 520 MPa; elongación hasta fractura: de 24,9 y 17,2 %; exponente de endurecimiento por deformación: 0,24 y 0,19; anisotropía normal: 1,64 y 1,29; anisotropía planar: 0,23 y -0,02. Los FLD0 determinados a partir de las curvas límite de formalidad (CLF) para las dos láminas de acero mostraron valores para ε1 de 0,281 y 0,336 respectivamente. Conclusiones: Aunque las propiedades intrínsecas (como A50, n y rm) de la lámina de acero SG295 presentan valores relacionados con una mayor formabilidad, las CLF muestran que el acero SG325 se desempeña ligeramente mejor debido a su mayor espesor

Construction of Formability Limit Curves for Low-Carbon Steels Used in the Manufacture of Pressure Cylinders

Context: The aim of this study is to determine the formability of SG295 (2,2 mm thick) and SG325 (2,3 mm thick) steel sheets, as well as their relationship with the sheets’ behavior in deep drawing and stretching operations. To this effect, chemical, metallographic, and mechanical analyses of the sheets were carried out. Method: The chemical analysis was carried out via optical emission spectrometry, and the metallographic structure was analyzed using the ASTM E3 standard. The intrinsic properties related to the formability of materials such as the elongation to fracture for a 50 mm gauge length, the conventional yield limit at 0,2% elongation, the ultimate strength, the strain hardening exponent, and the anisotropy coefficient at 15% elongation were determined through tensile tests according to ASTM E8M, ASTM E646, and ASTM 517. Forming limit curves were determined under ASTM E2218, for which a device was designed, built, and attached to a universal testing machine. Results: The results for the SG295 and SG325 steel sheets were as follows: tensile strength; 450 and 520 MPa; elongation at fracture: 24,9 and 17,2%; strain hardening exponent: 0,24 and 0,19; normal anisotropy: 1,64 and 1,29; planar anisotropy: 0,23 and -0,02. The FLD0 determined from the formality limit curves (FLCs) for the two steel sheets showed ε1 values of 0,281 and 0,336, respectively. Conclusions: Although the intrinsic properties (such as A50, n, and rm) of the SG295 steel sheet show values related to a greater formability, the FLCs show that SG325 steel performs slightly better due to its greater thickness

Global attitudes in the management of acute appendicitis during COVID-19 pandemic: ACIE Appy Study

Background: Surgical strategies are being adapted to face the COVID-19 pandemic. Recommendations on the management of acute appendicitis have been based on expert opinion, but very little evidence is available. This study addressed that dearth with a snapshot of worldwide approaches to appendicitis. Methods: The Association of Italian Surgeons in Europe designed an online survey to assess the current attitude of surgeons globally regarding the management of patients with acute appendicitis during the pandemic. Questions were divided into baseline information, hospital organization and screening, personal protective equipment, management and surgical approach, and patient presentation before versus during the pandemic. Results: Of 744 answers, 709 (from 66 countries) were complete and were included in the analysis. Most hospitals were treating both patients with and those without COVID. There was variation in screening indications and modality used, with chest X-ray plus molecular testing (PCR) being the commonest (19\ub78 per cent). Conservative management of complicated and uncomplicated appendicitis was used by 6\ub76 and 2\ub74 per cent respectively before, but 23\ub77 and 5\ub73 per cent, during the pandemic (both P < 0\ub7001). One-third changed their approach from laparoscopic to open surgery owing to the popular (but evidence-lacking) advice from expert groups during the initial phase of the pandemic. No agreement on how to filter surgical smoke plume during laparoscopy was identified. There was an overall reduction in the number of patients admitted with appendicitis and one-third felt that patients who did present had more severe appendicitis than they usually observe. Conclusion: Conservative management of mild appendicitis has been possible during the pandemic. The fact that some surgeons switched to open appendicectomy may reflect the poor guidelines that emanated in the early phase of SARS-CoV-2