Search Results (43)

Using the results from testing industrial batches of 23 mm steel heavy plates after thermomechanical rolling and subsequent post-weld heat treatment, the patterns of fatigue crack formation in the fracture specimens during CTOD (Crack Tip Opening Displacement) testing for fracture toughness are investigated. Visual, microstructural, and fractographic studies of the nature of fracture formation and the surface of the secondary separations have been conducted. The probable causes of the manifestation of the potential “pop-in” effect on the load–displacement diagrams of the notch opening displacement are described, as well as its potentially negative impact on the interpretation of test results. Full article

In this study, we used the depth-sensing indentation technique to determine the cracking resistance of different PVD hard coatings deposited on tool steel substrates. By comparison, with the load–displacement curves, measured at the sites of carbide inclusion and a tempered martensite matrix in the D2 tool steel substrate surface, we observed different fracture mechanisms on TiAlN hard coating prepared by sputtering. Additional information about the deformation and fracture phenomena was obtained from the SEM images of FIB cross-sections of both types of indents. We found that the main deformation mechanism in the coating is the shear sliding along the columnar boundaries, which causes the formation of steps on the substrate surface under individual columns. Using nanoindentation test, we also analyzed the cracking resistance of a set of nl-(Cr,Al)N nanolayer coatings with different Cr/Al atomic ratios, which were sputter deposited in a single batch. From the indentation curves, we determined the loads (F_c) at which the first pop-in appears and compared them with the plasticity index H³/E². A good correlation of both parameters was found. We also compared the indentation curves of the TiAlN coating, which were prepared by cathodic arc evaporation using 1-fold, 2-fold and 3-fold rotation of the substrates. Additionally, on the same set of samples, the fracture toughness measurements were performed by micro-cantilever deflection test. The impact of growth defects on the cracking resistance of the hard coatings was also confirmed. Full article

Understanding the impact of irradiation and temperature on the mechanical properties of GaN single crystals holds significant relevance for rational designs and applications of GaN-based transistors, lasers, and sensors. This study systematically investigates the influence of C-ion irradiation and temperature on pop-in events, hardness, Young’s modulus, and fracture behavior of GaN single crystals through nanoindentation experiments. In comparison with unirradiated GaN samples, the pop-in phenomenon for ion-irradiated GaN samples is associated with a larger critical indentation load, which decreases with increasing temperature. Both unirradiated and ion-irradiated GaN samples exhibit a decline in hardness with increasing indentation depth, while Young’s moduli do not exhibit a clear size effect. In addition, intrinsic hardness displays an inverse relationship with temperature, and ion-irradiated GaN single crystals exhibit greater intrinsic hardness than their unirradiated counterparts. Our analysis further underscores the significance of Peierls stress during indentation, with this stress decreasing as temperature rises. Examinations of optical micrographs of indentation-induced fractures demonstrate an irradiation embrittlement effect. This work provides valuable insights into the mechanical behavior of GaN single crystals under varying irradiation and temperature conditions. Full article

In this study, our objective is to investigate the anisotropic deformation behavior and the indentation size effect (ISE) of monocrystalline barium fluoride (BaF₂) using nanoindentation experiments with a diamond Berkovich indenter. BaF₂ is known for its anisotropy, which results in significant variations in its mechanical properties. This anisotropy poses challenges in achieving high processing quality in ultra-precision machining. Through our experiments, we observed numerous pop-in events in the load–displacement curves, indicating the occurrence of plastic deformation in BaF₂ crystals, specifically in the (100), (110), and (111) orientations; these pop-in events were observed as the indentation depth increased to 56.9 nm, 58.2 nm, and 57.8 nm, respectively. The hardness–displacement and elastic modulus–displacement curves were obtained from the tests exhibiting the ISE. The nanoindentation hardness of BaF₂ is found to be highly dependent on its crystallographic orientation. Similarly, for BaF₂ in the (100) orientation, the range is from 2.43 ± 0.74 and 1.24 ± 0.12 GPa. For BaF₂ in the (110) orientation, the values range from 2.15 ± 0.66 to 1.18 ± 0.15 GPa. For BaF₂ in the (111) orientation, the values range from 2.12 ± 0.53 GPa to 1.19 ± 0.12 GPa. These results highlight the significant influence of crystallographic orientation on the mechanical properties of BaF₂. To better understand the ISE, we employed several models including Meyer’s law, the Nix–Gao model, the proportional specimen resistance (PSR) model, and the modified PSR (mPSR) model, and compared them with our experimental results. Among these models, the mPSR model demonstrated the best level of correlation ($R^2>0.9999$) with the experimental measurements, providing a reliable description of the ISE observed in BaF₂. Our reports provide valuable insights into the anisotropic mechanical characteristics of BaF₂ materials and serve as a theoretical guide for the ultra-precision machining of BaF₂. Full article

In this study, nanoindentation tests at three different strain rates within 100 nm indentation depth were conducted on an a-plane ($11\overline{2}0$) ZnO single crystal to investigate the effect of strain rate on its nano-scale mechanical behavior. The load–indentation-depth curves, pop-in events, hardness and Young’s moduli of an a-plane ($11\overline{2}0$) ZnO single crystal at different strain rates were investigated at the nano-scale level. The results indicated that, with the indentation depth increasing, the load increased gradually at each maximum indentation depth, h_ma, during the loading process. A distinct pop-in event occurred on each loading curve except that corresponding to the h_max of 10 nm. The applied load at the same indentation depth increased with the increasing strain rate during the nanoindentation of the a-plane ($11\overline{2}0$) ZnO single crystal. The higher strain rate deferred the pop-in event to a higher load and deeper indentation depth, and made the pop-in extension width larger. The hardness showed reverse indentation size effect (ISE) before the pop-in, and exhibited normal ISE after the pop-in. Both the hardness and the Young’s modulus of the a-plane ($11\overline{2}0$) ZnO single crystal increased with the increasing strain rate, exhibiting the positive strain-rate sensitivity. Full article

A two-step bainitic treatment with a final isothermal temperature below M_S was adopted to obtain bainitic steel with abundant retained austenite (RA). Nanoindentation testing was used to investigate the stability of RA in bainite steel and clarify the effect of RA on the deformation of medium-carbon steel. The results showed that, in contrast to the traditional one-step approach, a greater amount of nanoscale RA film was obtained using the two-step treatment. This was due to a lower final bainitic transformation temperature, which induced a higher carbon concentration in the untransformed austenite in the stasis stage; this resulted in untransformed austenite with a higher carbon content existing as RA rather than forming martensite in the subsequent cooling process. In addition, it was determined that the increased stability of RA during the two-step transformation delayed the pop-in point. Full article

A surgical site infection (SSI) is an infection that occurs in the incision created by an invasive surgical procedure. Although most infections are treatable with antibiotics, SSIs remain a significant cause of morbidity and mortality after surgery and have a significant economic impact on health systems. Preventive measures are essential to decrease the incidence of SSIs and antibiotic abuse, but data in the literature regarding risk factors for SSIs in the pediatric age group are scarce, and current guidelines for the prevention of the risk of developing SSIs are mainly focused on the adult population. This document describes the current knowledge on risk factors for SSIs in neonates and children undergoing surgery and has the purpose of providing guidance to health care professionals for the prevention of SSIs in this population. Our aim is to consider the possible non-pharmacological measures that can be adopted to prevent SSIs. To our knowledge, this is the first study to provide recommendations based on a careful review of the available scientific evidence for the non-pharmacological prevention of SSIs in neonates and children. The specific scenarios developed are intended to guide the healthcare professional in practice to ensure standardized management of the neonatal and pediatric patients, decrease the incidence of SSIs and reduce antibiotic abuse. Full article

Pediatric neurosurgery is a highly specialized branch of surgery in which surgical site infections (SSIs) are potentially serious complications that can also adversely affect a good surgical outcome, compromising functional recovery and, in some cases, even putting the patient’s life at risk. The main aim of this consensus document is to provide clinicians with a series of recommendations on antimicrobial prophylaxis for neonates and children undergoing neurosurgery. The following scenarios were considered: (1) craniotomy or cranial/cranio-facial approach to craniosynostosis; (2) neurosurgery with a trans-nasal-trans-sphenoidal approach; (3) non-penetrating head injuries; (4) penetrating head fracture; (5) spinal surgery (extradural and intradural); (6) shunt surgery or neuroendoscopy; (7) neuroendovascular procedures. Patients undergoing neurosurgery often undergo peri-operative antibiotic prophylaxis, with different schedules, not always supported by scientific evidence. This consensus provides clear and shared indications, based on the most updated literature. This work has been made possible by the multidisciplinary contribution of experts belonging to the most important Italian scientific societies, and represents, in our opinion, the most complete and up-to-date collection of recommendations on the behavior to be held in the peri-operative setting in this type of intervention, in order to guide physicians in the management of the patient, standardize approaches and avoid abuse and misuse of antibiotics. Full article

The correlations among microstructure, surface morphology, hardness, and elastic modulus of Bi₂Te₃ thin films deposited on c-plane sapphire substrates by pulsed laser deposition are investigated. X-ray diffraction (XRD) and transmission electron microscopy are used to characterize the microstructures of the Bi₂Te₃ thin films. The XRD analyses revealed that the Bi₂Te₃ thin films were highly (00l)-oriented and exhibited progressively improved crystallinity when the substrate temperature (T_S) increased. The hardness and elastic modulus of the Bi₂Te₃ thin films determined by nanoindentation operated with the continuous contact stiffness measurement (CSM) mode are both substantially larger than those reported for bulk samples, albeit both decrease monotonically with increasing crystallite size and follow the Hall—Petch relation closely. Moreover, the Berkovich nanoindentation-induced crack exhibited trans-granular cracking behaviors for all films investigated. The fracture toughness was significantly higher for films deposited at the lower T_S; meanwhile, the fracture energy was almost the same when the crystallite size was suppressed, which indicated a prominent role of grain boundary in governing the deformation characteristics of the present Bi₂Te₃ films. Full article

Ocular surgery encompasses a wide range of procedures, including surgery of the tear ducts, eyelid, cornea and conjunctiva, lens, ocular muscle, and vitreoretinal and iris surgery. Operations are also performed for the removal of tumors, repairs of ocular trauma and, finally, corneal transplantation. Antibiotic prophylaxis for the prevention of surgical site infections (SSIs) in ocular surgery is a complex field in which shared lines of action are absent. In light of the scarcity of shared evidence in the use of ocular antimicrobial prophylaxis for the pediatric population, this consensus document aims to provide clinicians with a series of recommendations on antimicrobial prophylaxis for patients of neonatal and pediatric age undergoing eye surgery. The following scenarios are considered: (1) intraocular surgery; (2) extraocular surgery; (3) ocular trauma; (4) ocular neoplasm; (5) ocular surface transplantations; (6) corneal grafts. This work has been made possible by the multidisciplinary contribution of experts belonging to the most important Italian scientific societies and represents, in our opinion, the most complete and up-to-date collection of recommendations regarding clinical actions in the peri-operative environment in eye surgery. The application of uniform and shared protocols aims to improve surgical practice, through the standardization of procedures, with a consequent reduction of SSIs, also limiting the phenomenon of antimicrobial resistance. Full article

Surgical site infections (SSIs) represent a potential complication of surgical procedures, with a significant impact on mortality, morbidity, and healthcare costs. Patients undergoing cardiac surgery and thoracic surgery are often considered patients at high risk of developing SSIs. This consensus document aims to provide information on the management of peri-operative antibiotic prophylaxis for the pediatric and neonatal population undergoing cardiac and non-cardiac thoracic surgery. The following scenarios were considered: (1) cardiac surgery for the correction of congenital heart disease and/or valve surgery; (2) cardiac catheterization without the placement of prosthetic material; (3) cardiac catheterization with the placement of prosthetic material; (4) implantable cardiac defibrillator or epicardial pacemaker placement; (5) patients undergoing ExtraCorporal Membrane Oxygenation; (6) cardiac tumors and heart transplantation; (7) non-cardiac thoracic surgery with thoracotomy; (8) non-cardiac thoracic surgery using video-assisted thoracoscopy; (9) elective chest drain placement in the pediatric patient; (10) elective chest drain placement in the newborn; (11) thoracic drain placement in the trauma setting. This consensus provides clear and shared indications, representing the most complete and up-to-date collection of practice recommendations in pediatric cardiac and thoracic surgery, in order to guide physicians in the management of the patient, standardizing approaches and avoiding the abuse and misuse of antibiotics. Full article

For many years, it was clearly shown that surgical procedures might be associated with surgical site infection (SSI). Many scientific institutions prepared guidelines to use in surgery to reduce abuse and misuse of antibiotics. However, in the general guidelines for surgical antibiotic prophylaxis, plastic surgical procedures are not addressed or are only marginally discussed, and children were almost systematically excluded. The main aim of this Consensus document is to provide clinicians with recommendations on antimicrobial prophylaxis for pediatric patients undergoing plastic surgery. The following scenarios were considered: clean plastic surgery in elective procedures with an exclusive skin and subcutis involvement; clean-contaminated/contaminated plastic surgery in elective procedures with an exclusive skin and subcutis involvement; elective plastic surgery with use of local flaps; elective plastic surgery with the use of grafts; prolonged elective plastic surgery; acute burns; clean contused lacerated wounds without bone exposure; high-risk contused lacerated wounds or with bone exposure; contused lacerated wound involving the oral mucosa; plastic surgery following human bite; plastic surgery following animal bite; plastic surgery with tissue expander insertion. Our Consensus document shows that antimicrobial perioperative prophylaxis in pediatric patients undergoing plastic surgery is recommended in selected cases. While waiting the results of further pediatric studies, the application of uniform and shared protocols in these procedures will improve surgical practice, with a reduction in SSIs and consequent rationalization of resources and costs, as well as limiting the phenomenon of antimicrobial resistance. Full article

Surgical site infections (SSIs) represent a potential complication in surgical procedures, mainly because clean/contaminated surgery involves organs that are normally colonized by bacteria. Dental, maxillo-facial and ear-nose-throat (ENT) surgeries are among those that carry a risk of SSIs because the mouth and the first respiratory tracts are normally colonized by a bacterial flora. The aim of this consensus document was to provide clinicians with recommendations on surgical antimicrobial prophylaxis in neonates (<28 days of chronological age) and pediatric patients (within the age range of 29 days–18 years) undergoing dental, maxillo-facial or ENT surgical procedures. These included: (1) dental surgery; (2) maxilla-facial surgery following trauma with fracture; (3) temporo-mandibular surgery; (4) cleft palate and cleft lip repair; (5) ear surgery; (6) endoscopic paranasal cavity surgery and septoplasty; (7) clean head and neck surgery; (8) clean/contaminated head and neck surgery and (9) tonsillectomy and adenoidectomy. Due to the lack of pediatric data for the majority of dental, maxillo-facial and ENT surgeries and the fact that the recommendations for adults are currently used, there is a need for ad hoc studies to be rapidly planned for the most deficient areas. This seems even more urgent for interventions such as those involving the first airways since the different composition of the respiratory microbiota in children compared to adults implies the possibility that surgical antibiotic prophylaxis schemes that are ideal for adults may not be equally effective in children. Full article

The main aim of surgical antimicrobial prophylaxis (SAP) in urologic procedures is to prevent bacteraemia, surgical site infections (SSIs), and postoperative urinary tract infections (ppUTIs). Guidelines for SAP in paediatric urology are lacking. Only some aspects of this complex topic have been studied, and the use of antibiotic prophylaxis prior to surgical procedures seems to be more often linked to institutional schools of thought or experts’ opinions than to rules dictated by studies demonstrating the most correct and preferred management. Therefore, the aim of this Consensus document realized using the RAND/UCLA appropriateness method is to provide clinicians with a series of recommendations on SAP for the prevention of bacteraemia, SSIs, and ppUTIs after urologic imaging and surgical procedures in paediatric patients. Despite the few available studies, experts agree on some basilar concepts related to SAP for urologic procedures in paediatric patients. Before any urological procedure is conducted, UTI must be excluded. Clean procedures do not require SAP, with the exception of prosthetic device implantation and groin and perineal incisions where the SSI risk may be increased. In contrast, SAP is needed in clean-contaminated procedures. Studies have also suggested the safety of eliminating SAP in paediatric hernia repair and orchiopexy. To limit the emergence of resistance, every effort to reduce and rationalize antibiotic consumption for SAP must be made. Increased use of antibiotic stewardship can be greatly effective in this regard. Full article

Surgical site infections (SSIs) represent a potential complication in any type of surgery and can occur up to one year after the procedure in the case of implant placement. In the field of orthopedic and hand surgery, the rate of SSIs is a relevant issue, considering the need for the placement of synthesis devices and the type of some interventions (e.g., exposed fractures). This work aims to provide guidance on the management of peri-operative antibiotic prophylaxis for the pediatric and neonatal population undergoing orthopedic and hand surgery in order to standardize the management of patients and to reduce, on the one hand, the risk of SSI and, on the other, the development of antimicrobial resistance. The following scenarios were considered: (1) bloodless fracture reduction; (2) reduction of unexposed fracture and grade I and II exposed fracture; (3) reduction of grade III exposed fracture or traumatic amputation; (4) cruel fracture reduction with percutaneous synthesis; (5) non-traumatic amputation; (6) emergency intact skin trauma surgery and elective surgery without synthetic media placement; (7) elective orthopedic surgery with prosthetic and/or synthetic media placement and spinal surgery; (8) clean elective hand surgery with and without bone involvement, without use of synthetic means; (9) surgery of the hand on an elective basis with bone involvement and/or with use of synthetic means. This manuscript has been made possible by the multidisciplinary contribution of experts belonging to the most important Italian scientific societies and represents, in our opinion, the most complete and up-to-date collection of recommendations regarding the behavior to be adopted in the peri-operative setting in neonatal and pediatric orthopedic and hand surgery. The specific scenarios developed are aimed at guiding the healthcare professional in practice to ensure the better and standardized management of neonatal and pediatric patients, together with an easy consultation. Full article