Formability and hydroforming of anisotropic aluminum tubes

textThe automotive industry is required to meet improved fuel efficiency standards and stricter emission controls. Aluminum tube hydroforming is particularly well suited in meeting the goals of lighter, more fuel-efficient and less polluting cars. Its wider use in industry is hindered however by the reduced ductility and more complex constitutive behavior of aluminum in comparison to the steels that it is meant to replace. This study aims to address these issues by improving the understanding of the limitations of the process as applied to aluminum alloys. A series of hydroforming experiments were conducted in a custom testing facility, designed and constructed for the purposes of this project. At the same time, several levels of modeling of the process, of increasing complexity, were developed. A comparison of these models to the experiments revealed a serious deficiency in predicting burst, which was found experimentally to be one of the main limiting factors of the process. This discrepancy between theory and experiment was linked to the adoption of the von Mises yield function for the material at hand. This prompted a separate study, combining experiments and analysis, to calibrate alternative, non-quadratic anisotropic yield functions and assess their performance in predicting burst. The experiments involved testing tubes under combined internal pressure and axial load to failure using various proportional and non-proportional loading paths (free inflation). A number of state of the art yield functions were then implemented in numerical models of these experiments and calibrated to reproduce the induced strain paths and failure strains. The constitutive models were subsequently employed in the finite element models of the hydroforming experiments. The results demonstrate that localized wall thinning in the presence of contact, as it occurs in hydroforming as well as other sheet metal forming problems, is a fully 3D process requiring appropriate modeling with solid elements. This success also required the use of non-quadratic yield functions in the constitutive modeling, although the anisotropy present did not play as profound a role as it did in the simulation of the free inflation experiments. In addition, corresponding shell element calculations were deficient in capturing this type of localization that precipitates failure, irrespective of the sophistication of the constitutive model adopted. This finding contradicts current practice in modeling of sheet metal forming, where the thin-walled assumption is customarily adopted.Aerospace Engineering and Engineering Mechanic

Advances in Plastic Forming of Metals

The forming of metals through plastic deformation comprises a family of methods that produce components through the re-shaping of input stock, oftentimes with little waste. Therefore, forming is one of the most efficient and economical manufacturing process families available. A myriad of forming processes exist in this family. In conjunction with their countless existing successful applications and their relatively low energy requirements, these processes are an indispensable part of our future. However, despite the vast accumulated know-how, research challenges remain, be they related to the forming of new materials (e.g., for light-weight transportation applications), pushing the boundaries of what is doable, reducing the intermediate steps and/or scrap, or further enhancing the environmental friendliness. The purpose of this book is to collect expert views and contributions on the current state-of-the-art of plastic forming, thus highlighting contemporary challenges and offering ideas and solutions

An investigation of Hertzian contact in soft materials using photoelastic tomography

Hertzian contact of a rigid sphere and a highly deformable soft solid is investigated using integrated photoelasticity. The experiments are performed by pressing a styrene sphere of 15 mm diameter against a 44 x 44 x 47 mm$^3$ cuboid made of 5% wt. gelatin, inside a circular polariscope, and with a range of forces. The emerging light rays are processed by considering that the retardation of each ray carries the cumulative effect of traversing the contact-induced axisymmetric stress field. Then, assuming Hertzian theory is valid, the retardation is analytically calculated for each ray and compared to the experimental one. Furthermore, a finite element model of the process introduces the effect of finite displacements and strains. Beyond the qualitative comparison of the retardation fields, the experimental, theoretical, and numerical results are quantitatively compared in terms of the maximum equivalent stress, surface displacement, and contact radius dimensions. A favorable agreement is found at lower force levels, where the assumptions of Hertz theory hold, whereas deviations are observed at higher force levels. A major discovery of this work is that at the maximum equivalent stress location, all three components of principal stress can be determined experimentally, and show satisfactory agreement with theoretical and numerical ones in our measurement range. This provides valuable insight into Hertzian contact problems since the maximum equivalent stress controls the initiation of plastic deformation or failure. The measured displacement and contact radii also reasonably agree with the theoretical and numerical ones. Finally, the limitations that arise due to the linearization of this problem are explored

Clinical outcomes of Enhanced Recovery after Surgery Protocol for Hepato- pancreato- biliary Surgery; A Five-Year Experience from a Hellenic Oncological Hospital ERAS protocol and HPB surgery

Background: The development of enhanced recovery after surgery protocols (ERAS) for surgical intervention has contributed to reducing hospital length of stay and improved patient outcomes. Aim of the study was the assessment of the recovery time and cost-effectiveness of an ERAS protocol in oncological patients undergoing hepato- pancreato- biliary surgery (HPB) compared to conventional (CON) care.Methods: This prospective, open label, randomized trial, enrolled 283 patients who required hepatectomy or pancreatoduodenectomy. Eligible patients were stratified into hepatectomy or pancreatectomy groups then, randomly assigned to ERAS protocol (intervention) or CON care (control). The primary outcome of interest was post-operative recovery time (composite of; time to mobilization and oral intake) and secondary outcomes were cost effectiveness, dependance on post-operative opioids and post-operative complications (using the Clavien- Dindo classification). Results: The rate of complications for the patients underwent hepatectomy and treated in ERAS group was 18.18% compared to CON group, which was 40.9%. Whilst, of complications for the patients underwent pancreatectomy and treated in ERAS group was 15.94% compared to CON group, which was 38.2%.Conclusions: The ERAS protocol in this study significantly improved post-operative recovery time, reduced opioid dependance and reduced post-operative complications in patients undergoing HPB surgery. 

Histologically Malignant Solitary Fibrous Tumour of the Anterior Thoracic Wall: A Case Report and Review of the Literature

Solitary fibrous tumour (SFT) is a rare oncological entity that most often arises in the pleura. Over the past 10 years, the tumour has been described at numerous extrapleural locations. We present the case of a 42-year-old female Caucasian patient with an extrapleural SFT located at the anterior thoracic wall for 22 years, with atypical histological characteristics and clinical features of malignancy. Management consisted of a wide surgical resection, plastic reconstruction, and postoperative radiotherapy. Although extrapleural SFT usually behaves as a benign soft tissue tumour, it can also present with a more aggressive local behavior, including locoregional recurrence or metastasis. In that case, a multidisciplinary approach is required for accurate diagnosis and proper management

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Design of multi-step dies for sheet metal forming using a workpiece-performance-based approach: A preliminary study

Deep-drawn components are predominantly manufactured using multistep operations, e.g., in a progressive or transfer dies. Currently, intermediate die design is geometry-based and often neglects the influence of workpiece plastic flow during forming on the final part's mechanical performance. This approach results in non-homogeneous material deformation, inefficient material utilisation, wrinkling defects, and an increased risk of service failures. This study proposes an alternative workpiece-performance-based die-design approach for deep drawing, emphasising the critical role of material flow in determining the component's geometrical accuracy and mechanical properties. The strategy was experimentally tested on S420MC steel (1.8 mm thickness) square cups using two-step process chains: (1) a conventional method where the blank was partially drawn into a square cup, followed by full drawing, and (2) an alternative method starting with a circular blank partially drawn into a circular cup before full drawing to the square shape. Numerical analysis in AutoForm evaluates the evolution of effective plastic strain throughout the steps. The results demonstrate significant improvements, including more uniform strain distribution, a 7% wall thinning reduction, elimination of ironed wrinkles, and components with threefold increased strength and enhanced ductility. These findings highlight the potential of performance-based die design to improve material efficiency and structural reliability