Localized Necking Research Articles

On the prediction of ductile fracture in ship structures with shell elements at low temperatures

Abstract This paper proposes a practical method for addressing the effects of low temperatures on the ductile fracture behavior of high tensile strength steel plates and modeling using large shell finite elements. The test data of marine high-tensile strength steel grades, DH32, DH36, and EH36, at sub-zero temperatures were utilized. The tensile tests at sub-zero temperatures were simulated using fine solid elements to identify hardening law parameters. Simple localized necking loci were derived using the hardening curves of the steel grades considered. By defining the onset of localized necking as a failure condition, a simple fracture model for large shell finite elements that consider the low temperature effect was proposed. Several case studies were included to demonstrate the application and limitations of the proposed model.

Neck cooling induces blood pressure increase and peripheral vasoconstriction in healthy persons

IntroductionNoninvasive temperature modulation by localized neck cooling might be desirable in the prehospital phase of acute hypoxic brain injuries. While combined head and neck cooling induces significant discomfort, peripheral vasoconstriction, and blood pressure increase, localized neck cooling more selectively targets blood vessels that supply the brain, spares thermal receptors of the face and skull, and might therefore cause less discomfort cardiovascular side effects compared to head- and neck cooling. The purpose of this study is to assess the effects of noninvasive selective neck cooling on cardiovascular parameters and cerebral blood flow velocity (CBFV).MethodsEleven healthy persons (6 women, mean age 42 ± 11 years) underwent 90 min of localized dorsal and frontal neck cooling (EMCOOLS Brain.Pad™) without sedation. Before and after cooling onset, and after every 10 min of cooling, we determined rectal, tympanic, and neck skin temperatures. Before and after cooling onset, after 60- and 90-min cooling, we monitored RR intervals (RRI), systolic, diastolic blood pressures (BPsys, BPdia), laser Doppler skin blood flow (SBF) at the index finger pulp, and CBFV at the proximal middle cerebral artery (MCA). We compared values before and during cooling by analysis of variance for repeated measurements with post hoc analysis (significance: p < 0.05).ResultsNeck skin temperature dropped significantly by 9.2 ± 4.5 °C (minimum after 40 min), while tympanic temperature decreased by only 0.8 ± 0.4 °C (minimum after 50 min), and rectal temperature by only 0.2 ± 0.3 °C (minimum after 60 min of cooling). Index finger SBF decreased (by 83.4 ± 126.0 PU), BPsys and BPdia increased (by 11.2 ± 13.1 mmHg and 8.0 ± 10.1 mmHg), and heart rate slowed significantly while MCA-CBFV remained unchanged during cooling.ConclusionsWhile localized neck cooling prominently lowered neck skin temperature, it had little effect on tympanic temperature but significantly increased BP which may have detrimental effects in patients with acute brain injuries.

Granular cell tumour (Abrikossoff's tumor) in the ENT region: about two cases report

&lt;p class="abstract"&gt;Granular cell tumors also named Abrikossoff’s tumors, are very rare soft tissue tumors, almost always benign and can affect different organs. The head and neck location are the most common, particularly skin and the tongue. The larynx is concerned in 7 to 10% of the cervico-facial locations of this tumor (1, 2). In this article we report two cases of Abrikossoff’s tumor. The first case is of a 27 years old man, with no particular features in his medical history, who consulted for dysphonia, progressively evolving over 6 months. The nasal endoscopy found a whitish nodular lesion of almost 20 mm of diameter, involving the middle third of the right vocal cord. The tumor was removed under microlaryngoscopy. The second case is of ten days old newborn female, who presented dyspnea and dysphagia while breastfeeding, the clinical exam showed a round shaped lesion of 4 cm of diameter, implanted in the dorsal face of the tongue. The lesion was rooted out with electrocautery under general anesthesia. Anatomopathology examination with Immunohistochemistry of both patients’ surgical samples confirmed the diagnosis of granular cell tumor. The Origin of the Abrikossof’s tumors is uncertain. The recent immunohistochemical studies are orienting toward neurogenic origin. These tumors usually arise in the adult, between the ages of 20 to 60 years old, with female predominance. The symptoms are diverse and non-specific, only the anatopahtological examination permits to confirm the diagnosis. The main issues of these tumors are the compression of the adjacent structures and the high risk of recurrence, which requires long term surveillance.&lt;/p&gt;

Ductility of an ultrastrong glass-crystal nano-dual-phase alloy in sub-micron

We report an excellent tensile property of the Mg-based nano-dual-phase glass-crystal alloy in sub-micro size. It shows room temperature large ductility (>50% true strain, resulted from the localized necking deformation) with ultrahigh tensile strength (2.4 GPa), compared with 1.4 GPa strength and limited ductility of its metallic glass counterpart. To unraveling the underlying reasons, we have made transmission electron microscope (TEM) in-situ tensile investigation and molecular dynamic (MD) simulation for the materials, showing that homogenous plastic flow of nano-sized metallic glass phase activated by strain non-localization mechanism is responsible for the large ductility.

The role of strain localization on the electrical behavior of flexible and stretchable screen printed silver inks on polymer substrates

This work explores conductivity under applied uniaxial strain of two silver-based inks with similar flake volume fractions of ~50% that are screen-printed with a single pass (thickness: 10 µm) onto three different polymer substrates. The normalized resistance increases more rapidly with applied strain for the “flexible” ink (5025 with an acrylic binder), and has three times greater resistance at 35% strain when compared to the “stretchable” ink (PE874 with polyurethane binder). While resistance increase is qualitatively consistent with percolation theory, the in-situ strain map analysis and post-mortem fractography reveal drastic differences in the root causes of the inks’ electrical behavior. Both inks form strain localization bands with similar spacing. For the flexible ink (5025), strain localization is accompanied by local necking and flake fraction reduction. For the stretchable ink (PE874), strain localization is associated with surface cracking initiated by pre-existing voids, with minimal changes in the flake fraction. A model incorporating strain localization through a Gaussian distribution of flakes evolving with applied strain more closely accounts for the 5025 ink's normalized resistance increase compared to models that assume uniform strain and a uniform flake distribution. Overall, local necking and reduction of the flake fraction appear to be more detrimental to the resistance than the formation of surface cracks.

Formability prediction of Ti6Al4V titanium alloy sheet deformed at room temperature and 600 °C

Formability predictions of Ti6Al4V titanium alloy sheets deformed at room temperature and 600 °C, using D-Bressan’s shear stress rupture criterion and the critical strain gradient macroscopic modelling are presented and discussed in relation to limit strain results obtained experimentally. Ti6Al4V Forming Limit Strain Curves were predicted and compared with experimental curves at 25 °C and 600 °C and strain rate 0.1 s−1. The analytical models were calibrated by means of tensile tests performed on samples cut at 0°, 45° and 90° to the rolling direction at different temperatures and strain rates to obtain the Lankford coefficients and material strain and strain rate hardening behavior. The applied critical shear stress rupture criterion showed to give a fairly good fit with experimental limit strains outcomes, proving that the shear stress rupture nature of specimens deformed at room and elevated temperatures were well reproduced, despite a not-null strain rate sensitivity coefficient at 600 °C. Fracture occurrence by fast shear stress mechanism through thickness direction was corroborated by experimental fractograph observations close to fracture surfaces. It was shown that predicted limiting major true strain of fracture by shear stress curve is governed by normal anisotropy, strain hardening exponent, pre-strain and normalized critical shear stress parameter, which depends on temperature and strain rate whereas the strain hardening exponent depends largely on temperature. In contrast, the critical strain gradient modelling for onset of localized necking showed poor correlation with the experimental limit strains. Best fit of the critical shear stress criterion with experimental limit strain curves was given by specimens deformed near plane strain or FLCo. Hence, a common feature of various strain-rate independent metals, annealed or cold rolled, is that the main fracture mechanism of thin sheet metals can be considered as fast shear stress through sheet thickness without a visible localized necking in biaxial stretching.

Material modeling and simulation of continuous-bending-under-tension of AA6022-T4

In earlier contributions, we discussed continuous-bending-under-tension (CBT) experiments on AA6022-T4. We found that CBT significantly enhanced the elongation-to-fracture and strength, over uniaxial tension. In the present paper, our understanding of CBT is expanded beyond these experimental observations, with the aid of material modeling and numerical simulations of the process. Cyclic tension-compression experiments were performed on this material, using strain histories that are expected to replicate the loading during CBT, i.e., different combinations of constant strain amplitude and linearly increasing mean value, to failure. During these experiments, a limited but not negligible amount of kinematic hardening was discovered. Some of these experiments are used for calibration of a combined isotropic-kinematic hardening model, while the rest are used for experimental validation of the model. The modeling framework is based on a rate-independent, associated flow rule with the von Mises yield criterion as the plastic potential. Isotropic hardening is introduced by a simple, exponential-decay model of the growth of the yield surface with plastic deformation. Non-linear kinematic hardening is introduced by a 4-term, Chaboche-type model. The large strain hardening curve is identified by extrapolation, an approach that is validated later in the work and contrasted with alternative options. This material modeling framework is introduced in finite element models of the CBT process. The model is meshed with linear, reduced-integration elements, with 7 elements through the thickness. It is found that the numerical model reproduces the experimental force-displacement curve, including the succession of spikes and plateaus typical of CBT, very closely. The model also replicates the development of strain on the surface during CBT, and compares well with post-test strain measurements. After these validations, the model is used to probe the mechanics of the CBT process, e.g., the development of stress and strain through the thickness and per cycle, the location and onset of failure, as well as the failure angle, which in CBT differs from the localized neck angle found in a typical uniaxial tension experiment.

Low formability and reduction of area in twinning-induced plasticity steels despite their excellent tensile elongation

The mechanism for low formability and reduction of area (RA) in twinning-induced plasticity (TWIP) steels despite their excellent tensile elongation has been investigated in an attempt to understand and increase their formability. In metals, RA is strongly dependent on the post-necking elongation (PE) rather than uniform elongation (UE); in this study, UE and PE had 9% and 91% contributions to RA, respectively. Between the two representative ductility indicators in tensile tests, the RA is typically higher than the total elongation (TE) in conventional metals. However, the RA of TWIP steels was lower than the TE because TWIP steels had a higher UE and lower PE. This was attributed to the higher strain hardening exponent (n) and lower strain rate sensitivity (m) of TWIP steels. This indicates that TWIP steels have a higher resistance to fracture by the strain gradient, but a lower resistance to fracture by the strain rate gradient. In this study, the small and/or negative m value of TWIP steels reduced the RA value and formability in spite of their higher elongation. The negative m value led to a strain concentration at the necking region, leading to localized necking without diffuse necking followed by shear cracks, resulting in the lower RA and formability. Consequently, it is necessary to increase the m value of TWIP steels in order to increase the formability.

A theoretical prediction framework for the construction of a fracture forming limit curve accounting for fracture pattern transition

It has been accepted that the formability of a sheet metal with a moderate ductility can be limited by not only localized necking (LN), but also ductile fracture (DF). In this study, a theoretical prediction framework is developed for a comprehensive formability characterization, in which forming limit curves at LN (FLCN) and DF (FLCF) are elaborately correlated by considering strain path evolution. A dual-phase steel material (DP590 sheet metal) is selected with a series of DF and Nakajima tests performed. A newly proposed DF model (uncoupled type) is calibrated by implementing a hybrid experiment-simulation method in line with the DF tests, which are designed to achieve DF under distinct stress states, such as simple shear (SS), uniaxial tension (UT), plane strain tension (PST), and balanced biaxial tension (BBT). The resulting three dimensional (3D) fracture surface demonstrates a good agreement with the tested data. The modified maximum force criterion (MMFC) is selected for the theoretical identification of strain path evolution. The calibrated MMFC results in a FLCN exhibiting a certain level of underestimation as compared to the tested data in the range of positive minor strain. The MMFC is improved (iMMFC) by incorporating with an initial strain path-based function for a higher accuracy in characterizing evolutive strain paths; the resulting FLCN is observed to have a better performance than that of MMFC. Theoretical FLCFs are determined by the integral of ductile damage increment (defined by the DF model calibrated) over each identified strain path from UT to BBT. After considering strain path evolution, different deformation stages are added into the finalized forming limit diagrams including both FLCF and FLCN. It is found that the FLCF based on iMMFC model demonstrates acceptable deviations as compared to all the tested cracking data. Moreover, this FLCF intersects with the corresponding theoretical FLCN as load path approaches from UT to BBT, representing a fracture pattern transition from a LN band-accompanied DF to the one without LN band; this prediction is further validated by experimental observations. The FLCF based on MMFC fails to predict this transition behavior. The current study confirms the presence of a competition between LN-induced failure and DF-induced failure for sheet metals. Moreover, all of these findings advance the insight into the importance of performing a DF prediction aside of a FLCN prediction, especially for the case where a sheet metal with a moderate ductility shows a fracture pattern transition behavior.

Comparative study of ASS 316L on formability at room temperature and super plastic region

ABSTRACT In the sheet metal industry, hot forming of high strength sheet metal alloys such as austenitic stainless steels (ASSs) are in great demand. Identifying the safe strain region is essential to avoid failures and reduce the wastage. Forming limit diagram (FLD) is a vital tool which is used to describe the maximum limit of principal strains that can be sustained by sheet metals till the onset of localised necking. These diagrams are also useful in comparing the changes in forming characteristics of the material with changes in process parameters like temperature, orientation and speed of deformation. The present study aimed at comparing the experimental FLD for ASS 316L at room temperature and 900°C by stretch forming. These specimens are cut in three different orientations (0°, 45° & 90°) to the rolling direction and experiments are conducted at a strain rate of 0.1/s. It is reported that, the specimens from rolling direction are among the stronger samples. The change in formability characteristics of ASS 316L with changes in temperatures using FLD has been observed. The optical microscopy and scanning electron microscopy is analysed to understand the fracture morphologies. The comparison between these set of results indicates that there is significant increase in formability of material. Abbreviations ASS: Austenitic Stainless Steel; RT: Room Temperature; FLD: Forming Limit Diagram; FFLD: Fracture Forming Limit Diagram; SEM: Scanning Electronic Microscopy; LDH: Limiting Dome Height; UTS: Ultimate Tensile Strength; YTS: Yield Tensile Strength; K: Strength Factor; n: Strain Hardening Exponent

Clinical Profile of Patients with Head and Neck Amyloidosis: A Single-Institution Retrospective Chart Review.

Introduction Isolated amyloidosis involving the head and neck is a rare entity. The pathophysiology of the localized disease appears to be distinct from that of the systemic counterpart. Systemic progression of the localized disease is unusual, and the prognosis of the localized form is excellent. Objective To describe the demographic and clinicopathological characteristics of patients presenting with localized head and neck subsite amyloidosis. Methods A retrospective chart review of the patients with head and neck amyloidosis identified by the electronic search of the electronic database of the Departments of Pathology and Otorhinolaryngology was performed. The various demographic and clinical data were tabulated. Results In total, seven patients (four females, three males) with localized head and neck amyloidosis (three supraglottic, three lingual and one sinonasal) were identified. Six patients had AL-amyloid deposits, and one patient had AA-amyloid deposits. Supraglottic involvement and that of the base of the tongue were treated surgically using CO2 laser, and these patients were disease-free at the last follow-up. The patient with sinonasal amyloidosis experienced symptom recurrence after six months of the functional endoscopic sinus surgery. All of the patients were screened for systemic amyloidosis with abdominal fat pad biopsy, and were found to be free of systemic spread. Conclusion Isolated head and neck amyloidosis, as opposed to systemic amyloidosis, has an excellent prognosis in terms of survival. Therefore, systemic amyloidosis should be excluded in all cases. The treatment of choice remains surgical excision; however, watchful waiting may be a suitable strategy for mild symptoms or for cases in which the disease was discovered incidentally.

The effectiveness of acupuncture in the management of persistent regional myofascial head and neck pain: A systematic review and meta-analysis

Persistent head and neck myofascial pain is among the most frequently reported pain complaints featuring major variability in treatment approaches and perception of improvement. Acupuncture is one of the least invasive complimentary modalities that can optimize conventional treatment. The aim of this review was to determine the evidence for the effectiveness of acupuncture in the management of localized persistent myofascial head and neck pain. Only randomized controlled clinical trials (RCTs) were included. The search was conducted in PubMed, Ovid Medline, Embase, Google Scholar, and Cochrane Library in addition to manual search. The main outcome measure was the comparison of the mean pain intensity score on VAS between acupuncture and sham-needling/no intervention groups. Safety data and adherence rate were also investigated. Six RCTs were identified with variable risk of bias. All included studies reported reduction in VAS pain intensity scores in the groups receiving acupuncture when compared to sham needling/no intervention. Meta-analysis, using a weighted mean difference as the effect estimate, included only 4 RCTs, revealed a 19.04 point difference in pain intensity between acupuncture and sham-needling/no intervention (95 %CI: -29.13 to -8.95). High levels of safety were demonstrated by the low rates of side effects/withdrawal. Inconsistency in reporting of outcomes was a major limitation. In conclusion, moderate-quality evidence suggests that acupuncture may be an effective and safe method in relieving persistent head and neck myofascial pain. Optimizing study designs and standardizing outcome measures are needed for future RCTs.

The impacts of intra-arterial chemotherapy on head and neck microvascular reconstruction

For locally advanced head and neck cancers, intra-arterial (IA) chemotherapy is utilized for locoregional control with favorable results. The study aimed to evaluate the surgical outcomes of microsurgical reconstruction in head and neck cancer patients with IA chemotherapy METHODS: This cohort study retrospectively reviewed patients who underwent head and neck microsurgical reconstruction from January 2014 to August 2018. Patients with prior history of chemotherapy were included and categorized into two groups according to history of IA chemotherapy (IA group)/intravenous chemotherapy (IV group). Flap survival was evaluated along with microsurgical revision rates and complications. Recipient vessel specimens were analyzed by histological examination. A 1:1 propensity score matched analysis was performed. The study cohort included 45 patients with IA chemotherapy and 201 patients with IV chemotherapy. After propensity score matching, the difference in total flap loss and microsurgical revision rates were nonsignificant between two groups. However, the IA group had significantly higher rates of arterial thrombosis (Odds ratio [OR] 4.98; 95%CI, 1.28-19.38; p=0.021), wound-related complications (OR 3.30; 95%CI, 1.21-9.02; p=0.02) and revision surgery within one month (OR 3.73; 95%CI, 1.10-12.64; p=0.035). Based on histology, IA group vessels showed a higher intima/media ratio than the IV group (0.45±0.06 versus 0.23±0.03, p=0.02) CONCLUSION: Despite treating local advanced head and neck cancers with good results, IA chemotherapy may cause subsequent deleterious effects on local tissue due to the high concentration of cytotoxic chemotherapeutic agents. Surgeons should be cautious in selection of recipient vessels when performing microvascular reconstruction.

Topografia e morfometria do timo em aves (Gallus gallus domesticus) da linhagem Ross 308 AP (AP95)

Resumo Objetivou-se descrever a topografia e morfometria do timo em 30 aves domésticas da linhagem Ross 308 AP (AP95), 15 machos e 15 fêmeas, com idade de 14 a 16 semanas e massa corporal média de 2,1 kg e 1,7 kg, respectivamente nos machos e fêmeas. Após a fixação em solução aquosa de formol a 10%, as peças foram dissecadas. Os lobos tímicos localizavam-se desde o terço cranial do pescoço até os ossos claviculares, de forma linear, longitudinal e lateralmente no pescoço, paralelos ao nervo vago, veia jugular externa e artéria comum do nervo vago. Os lobos apresentaram formatos ovalados e triangulares e o número foi de quatro a oito. Agrupando os lobos de acordo com a localização no pescoço, nos terços cranial, médio e caudal, as médias de comprimento x largura x espessura variaram, nessa ordem, de 1,93 a 52,1 mm, 0,98 a 23,15 mm e 0,32 a 8,52 mm. O timo das aves AP95 apresentou características topográficas e morfológicas similares àquelas de outras linhagens, porém, quanto à morfometria, foram observadas características singulares.

Cranial nerve schwannoma - A pictorial essay.

Schwannomas are peripheral nerve sheath tumours arising from cranial, spinal or peripheral nerves. Most of the schwannomas are benign with the rare possibility of malignant transformation. Cranial nerve schwannomas can be seen along the course of any cranial nerve in the intracranial region or head and neck location. Although a majority are solitary sporadic lesions, multiple schwannomas can be seen in syndromes like neurofibromatosis type 2 and rarely in type 1. Since intracranial schwannomas are slow-growing, clinical presentation varies between no symptoms to cranial nerve palsy. Most of the times, the symptoms are due to mass effect over the adjacent structures, foraminal widening, compression of other cranial nerves, denervation injury or hydrocephalus. Familiarity with the course of the cranial nerves, imaging appearances and clinical presentation of schwannomas helps in accurate diagnosis and possible differential diagnosis, especially in uncommon clinical and radiological appearances. In this pictorial review, we illustrate relevant anatomy of cranial nerves, imaging features of schwannomas of most of the cranial nerves, clinical presentation and differential diagnosis.

Suicidal ,Homicidal and Accidental Hanging : Comparative Cross Sectional Study in Aljabal Alakhdar Area,Libya.

Background:Death by hanging may be suicidal, accidental or homicidal. However, as most hangings are suicides, the possibility of a non-suicidal death by hanging sometimes taken into consideration when there is evidence supporting this suspicion.General external appearances, Local external neck findings, neck autopsy andneck histological changes play major role in differentiation between types of hanging. Aims & Objectives:to differentiate between types of hanging (suicidal, homicidal and accidental) by using different diagnostic methods includes naked eye examination, neck autopsy, examination of neck structure, and the histopathological features of neck structures at the ligation mark site: A study carried out in Department of Forensic Medicine and Clinical Toxicology, Zagazig University, Egypt from March 2018 to March 2019 with 36 cases of deaths due to hanging. A thorough external and internal examination of neck structure was performed in all the cases. Results: A total of 36 cases were notified. Majority, Suicidal hanging associated with female sex (57.1%) of cases. homicidal and accidental hanging significantly associated with skin haemorrhage in (80%) of cases. Microscopic examination: breaking, wrinkling and compression of skin along with micro haemorrhages in subcutaneous tissues were notified which commonly associated with homicidal hanging. Conclusion: The examination of corpse in hanging cases is made easy by correlating current observation with the autopsy finding. The correlation of external, internal and microscopic findings leads to easy formulation of final opinion these cases. It also, to some extent helps to differentiate between types of hanging.

Material Modeling in High Strain Range and Forming Limit Analysis for 6000 Series Aluminum Alloy Sheet

This study investigates the effects of material modeling in high strain range on the forming limit analysis of a 6000-series alloy sheet 6016-T4. A servo-controlled tension-internal pressure testing machine was used to measure the multiaxial plastic deformation behavior in a strain range from initial yield to fracture. Tubular specimens were fabricated with a weld line thicker than the sheet thickness to prevent fracture from occurring in the weld zone. Proportional loading in the first quadrant of the principal stress space was applied to the specimens to measure the forming limit curve (FLC) and forming limit stress curve (FLSC), in addition to the contours of plastic work and the directions of plastic strain rates. Moreover, forming limit strains were measured using a flat-headed punch stretching test (PST). From the multiaxial tube expansion test (MTET) data, although a differential hardening effect was observed, appropriate coefficients including the exponent of the Yld2000-2d yield function (Barlat et al, 2003) were determined and employed in the Marcińiak-Kuczyski (1967) forming limit analysis (M-K analysis). The calculated forming limit strains in the vicinity of equibiaxial tension were smaller than the measured ones. The M-K analysis predicted that the forming limit strain in the vicinity of equibiaxial tension becomes minimum when the inclination angle of the localized neck from the rolling direction (RD) is 45° (diagonal direction; DD) while the experimental fracture direction was the RD. With the additional MTET, the plastic deformation behavior in the DD was measured and compared with that calculated from the material model. The reason of the discrepancy in the fracture direction between the experiment and the M-K approach is discussed.

Predictions of Forming Limit Curves of AA6014 Aluminium Alloy at Room Temperature

The aim of present work is to examine D-Bressan mathematical model to accurately predict the surface limit strains by the critical fast shear stress criterion of conventional AA6014 aluminium alloy sheets, after loading with non-linear strain paths at room temperature. Two kinds of limit strain curves can be plotted in the Map of Principal Surface Limit Strains (MPLS): the surface local necking limit, FLC-N, and the fast shear stress fracture limit curve FLC-S. D-Bressan´s critical shear stress criterion model combined with Barlat´s Yld 2000-2D yield criterion is proposed for theoretical prediction of FLC-S curve in sheet metal forming operations and were compared with experimental outcomes of AA6014. In order to calibrate the Bressan-Barlat macroscopic model, tensile tests at two different strain rates on specimens cut at 0o, 45o and 90o to the rolling direction and bulge test were carried out at room temperature to obtain the material coefficients of plastic anisotropy, strain and strain rate hardening law. Experimental bi-linear strain paths were carried out in specimens with 1.04 mm thickness by pre-stretching in uniaxial stress direction up to two strain levels before performing Nakajima testing experiments for obtaining the forming limit strain curves. D-Bressan critical fast shear stress modelling, combined with Barlat´s Yld 2000-2d yield function, predicted quite well both formability of AA6014 sheet as received and the reduced FLC-S after 10% and 20% uniaxial pre-stretching and bi-linear strain path. Comparisons of experimental FLC-S and predictions with Barlat´s Yld 2000-2D and Hill 79 yield criteria were analyzed and discussed. D-Bressan approach with Barlat´s Yld 2000-2d yield function, for exponent m=6, provided better fitting to the experimental FLC-S curves than D-Bressan model combined with Hill 79 yield function.

A Rare Case of Coexisting Subaortic and Submitral Left Ventricular Aneurysms

Subvalvar left ventricular aneurysm is a rare disorder. Commonly it occurs below the posterior annulus of the mitral valve. Rarely the aneurysm may be found below the aortic annulus. Coexistence of both aortic and submitral aneurysms is still rarer. Here is a 58-year-male who presented with heart failure. Echo revealed an aneurysm below the aortic annulus adjacent to right coronary cusp collapsing in diastole and enlarging in systole. Doppler interrogation showed flow into and out of aneurysm from left ventricle and mild aortic regurgitation. In addition there was a submitral aneurysm below the posterior mitral leaflet with a single localised neck and mild mitral regurgitation. There was evidence of moderate left ventricular systolic dysfunction and grade II diastolic dysfunction with features of right heart failure. He was given diuretics and referred for surgery.

A comparative study on microstructure, physical-mechanical properties, and self-healing performance of two differently synthesized nanocomposite double network hydrogels based on κ-car/PAm/GO

Physical-chemical double network (DN) hydrogels have been well recognized as new tough materials with unique structural platforms demonstrating a collection of various properties including superior mechanical strength, remarkable toughness recovery and self-healing property into a single material. However, a comprehensive study on the effect of synthesis methods of DN hydrogels is very critical as they influence their properties and performances. This study is aimed at investigating the effect of two different synthesis methods of thermal-curing and UV-curing on microstructure and physical-mechanical properties including self-healing capability, swelling and water-retaining capacity, as well as electrical conductivity of the κ-carrageenan (κ-Car)/polyacrylamide (PAm) DN hydrogel. Compared to the thermal-cured DN hydrogel, the UV-cured DN hydrogel has exhibited different mechanical behavior (plastic-like with localized necking vs. elastomeric-like), excellent mechanical properties (failure stress = 0.42 MPa vs. 0.12 MPa, failure strain = 2079%, vs. 722%, elastic modulus = 0.1 MPa vs. 0.069 MPa, and fracture energy = 3.54 MJ/m3 vs. 0.50 MJ/m3), and much greater self-healing capability. These could be explained in terms of reducing the contribution of the κ-Car physical network and also reversible interactions in the favor of increasing the cross-link density of PAm chemical network as a consequence of grafting reaction in the thermally-cured hydrogel, although the non-uniform lamellar-like structure in thermally-cured hydrogel could also play a role. By focusing on the linear and nonlinear rheological measurements, it was also demonstrated that the UV-curing method has resulted in much better thermo-reversibility of the hydrogel as a valuable property that can significantly extend the application of the κ-Car/PAm DN hydrogels. An attempt was also made to explore the effect of synthesis methods on the microstructure and physical-mechanical performance of the k-Car/PAm DN hydrogels in presence of GO nanosheets. In both synthesis methods, the presence of GO was found to have an enhancing effect on the properties of DN hydrogels. In the case of thermally-cured hydrogels, a partial reduction of GO was occurred which could, in turn, affect the performance of the hydrogels. It is hoped that this knowledge can contribute to a better understanding of the correlation between microstructure and different properties of hydrogels to precisely design a structural DN hydrogel with a special performance for the desired applications.