Unstable Neck Research Articles

Analysis of the Temperature Evolution at Necking during Tensile Deformation of H240LA Steel Sheets

The study of localized necking based on strain analysis using Digital Image Correlation (DIC) is the most widely used technique in sheet metal forming to study the FLD (Forming Limit Diagram). However, due to the heat generated by plastic deformation during the forming operations, another way is to analyze the temperature field of the specimen during the test by using Digital Infrared Thermography (DIT). A series of Nakazima tensile tests of high-strength low-alloy steel were tested using DIC and DIT synchronized systems. In this study, a thermomechanical numerical model was developed in ABAQUS/Standard in order to study the energy balance between the different effects of heat generation by plastic deformation, and transient conductive and convective heat transfers through the sample and to the environment. Analysis of the predicted energy balance during the tests allowed to understand the temperature evolution observed both at the beginning and at the development of the unstable necking until fracture. The numerical results are consistent with the analysis obtained from experimental temperature field, making feasible the use of DIT systems to study new necking detection criteria.

Revisiting stress-oscillation in cold drawing of poly(ethylene terephthalate)

This paper investigates the unusual phenomenon of stress-oscillation (SO) where a polymer exhibits periodic oscillatory neck propagation during drawing. It has been suggested that heat generation at the neck is critical, while other theories propose that an unstable neck stress is the controlling mechanism. Here, we study cold-drawing of poly(ethylene terephthalate) at 100 mm min−1 where SO has been monitored by thermal analysis. The morphology of the transparent and opaque bands were investigated using DSC, X-ray scattering and microscopy. It is revealed that heat release is a consequence of the plastic deformation as opposed to being the cause of the yielding. Neck geometry plays a key role in the mechanism. Temperature rise at the neck is low (9 °C) and does not lead to a change in crystalline morphology between the transparent and opaque bands. It is concluded that stress-induced crystallization plays no role in the SO process for cold drawn PET and that the opaque bands result from axial voiding during high strain-rate yielding.

Finite element analysis of new headless compression supporting screw for the treatment of unstable femoral neck fracture.

Femoral neck fracture is an unsolved challenge in orthopedics. The complication rate in particular is high. There remains a lack of consensus on the optimal choice of internal fixation for unstable femoral neck fracture. The study aimed to develop a new headless compression supporting screw (HCSS) for the treatment of unstable foemoral neck fracture. We designed a new HCSS and used a femoral neck fracture (Pauwels III fracture) model (left, fourth-generation composite, Sawbones) and three-dimensional finite element analysis to compare the biomechanical performance of HCSSs with that of cannulated compression screws (CCSs) for treatment of unstable femoral neck fracture. Maximum displacement, peak von Mises stress, peak strain, and rotation for the HCSS were smaller than those for the CCS. The stress was more widely distributed for the HCSS, whereas the stress was concentrated for the CCS. The HCSS resulted in better biomechanical stability than that from the CCS. For Pauwels III fractures the HCSS exhibits better resistance to shear forces and better support, providing a new clinical treatment.

Temperature-dependent tensile properties of polyamide 12 for the use in percutaneous transluminal coronary angioplasty balloon catheters

BackgroundPercutaneous transluminal coronary angioplasty (PTCA) balloon catheters must withstand high pressures required for the lesion treatment, pushing loads during insertion, and pulling loads during withdrawal. These loads pose a challenge especially for polymeric tubular shafts with small cross sections. In order to enable new design innovations and to better understand the mechanics of current catheter technologies, the tensile properties of polyamide (PA) 12 were investigated. PA 12 dog bone specimens and medical PA 12 tubes were either stored at ambient temperature and humidity or conditioned in water, and subjected to tensile loads at different temperatures. In addition, the effect on the tensile properties of the necking process, a forming process to reduce the wall thickness of the tubes, was determined.ResultsThe tested tubes showed a reduction in both Young’s Modulus (− 41.5%) and yield stress (− 29.2%) compared to standardized specimens. Furthermore, an increase in temperature and water absorption softens the material and reduces the mechanical properties like the Young’s Modulus and the yield stress. It was found that the material strengthens during the necking process. Likely due to the orientation of the polymers chain molecules in load direction (Rösler et al., 2007), the Young’s Modulus of the material could be increased by 43.5%. Furthermore, the absence of a yield point after necking allows for a greater loading capacity of the material without unstable neck growth. Besides the strengthening, the ultimate strain is reduced by 50%. This indicates that the necking process induces plastic deformation.ConclusionThe investigation showed that the environmental conditions like temperature and humidity can influence mechanical properties. It could also be shown that pre-forming processes such as necking can enhance the mechanical properties, such as the Young’s Modulus, while reducing the wall thickness. These findings suggest possible further development of catheters with a small cross section and higher mechanical strength and highlight the importance to account for the targeted operating temperature during the design process.

Visualization of Bubble Nucleation and Growth Confined in 2D Flakes.

The nucleation and growth of bubbles within a solid matrix is a ubiquitous phenomenon that affects many natural and synthetic processes. However, such a bubbling process is almost "invisible" to common characterization methods because it has an intrinsically multiphased nature and occurs on very short time/length scales. Using in situ transmission electron microscopy to explore the decomposition of a solid precursor that emits gaseous byproducts, the direct observation of a complete nanoscale bubbling process confined in ultrathin 2D flakes is presented here. This result suggests a three-step pathway for bubble formation in the confined environment: void formation via spinodal decomposition, bubble nucleation from the spherization of voids, and bubble growth by coalescence. Furthermore, the systematic kinetics analysis based on COMSOL simulations shows that bubble growth is actually achieved by developing metastable or unstable necks between neighboring bubbles before coalescing into one. This thorough understanding of the bubbling mechanism in a confined geometry has implications for refining modern nucleation theories and controlling bubble-related processes in the fabrication of advanced materials (i.e., topological porous materials).

Bipolar hemiarthroplasty versus total hip replacement in displaced femoral neck fracture in elderly

Introduction: Fractures of the neck of the femur are commonly seen in the geriatric population resulting in significant morbidity and mortality. Primary arthroplasty helps in rapid mobilization while decreasing the chances of implant failure and complications such as deep vein thrombosis, pulmonary complications, infection, and bedsores. The purpose of this can be fulfilled either by Bipolar Hemiarthroplasty as well as by Total Hip arthroplasty. The aim of this study is to determine whether total hip replacement is clinically and functionally better than bipolar hemiarthroplasty in the neck of femur fracture in older patients. Method: It is a prospective study done at Sri Ramachandra Medical College, Chennai, and Velammal Medical College, Madurai on 70 patients diagnosed with the unstable neck of femur fractures who were treated with bipolar hemiarthroplasty and total hip replacement from April 2018 to September 2019. The inclusion criteria were age more than 60 years and Unstable neck of femur fractures as per the Garden classification. The exclusion criteria were pathological fractures, associated fracture of lower limbs, and non-ambulatory patients prior to the injury. A functional assessment was carried out using the Harris Hip Score. Results: In the group that underwent a total hip replacement, the mean Harris Hip Score was 70.6, 74.4, 77.68 and 80.95 at the follow-up visits at week 6, 3 months, 6 months and 1 year respectively. In the group that underwent bipolar hemiarthroplasty, the mean Harris Hip Scores were 63.50, 66.25, 68.72, and 71.26 at the follow-up visits at week 6, 3 months, 6 months and 1 year respectively. Conclusion: Total hip arthroplasty is recommended over hemiarthroplasty for the displaced neck of femur fractures in elderly patients owing to the higher Harris Hip Scores and lower re-operation rates.

The effects of the neck stabilization exercise on the muscle activity of trunk respiratory muscles and maximum voluntary ventilation of chronic stroke patients

Unstable neck posture, muscle imbalance, and segmental instability can cause neck pain and decrease the respiratory function. To examine effects of a neck stabilization exercise on respiratory muscle activity and maximal voluntary ventilation (MVV) in patients with a chronic stroke. A total of 40 patients with a chronic stroke participated in this study. They were randomly divided into two groups (20 in each group). However, ten patients dropped out of the experiment (5 in each group). The experimental group (n= 15) performed a 15-minute neck stabilization exercise and a 15-minute breathing retraining exercise in addition to a rehabilitation exercise treatment. The control group (n= 15) completed a 30-minute breathing retraining exercise in addition to a rehabilitation exercise treatment. Exercises were conducted for 30 minutes a day, five times a week, for a total of six weeks. Activities of major respiratory muscles and MVV were measured before and after the experiment. Both the experimental group and the control group showed significant difference in activities of major respiratory muscles and MVV before and after the experiment (p< 0.05). The experimental group showed a significantly higher increase compared to the control group (p< 0.05). The application of a combination of a neck stabilization exercise and a breathing retraining exercise to patients with a chronic stroke can increase activity of respiratory muscles and MVV.

Unstable necking due to deformation softening of polybutylene succinate

Self-oscillating neck propagation of amorphous polybutylene succinate was studied. The neck propagated by regular neck front jumps at the stretching speeds from 0.05 to 1000 mm/min. Self-oscillations at extremely low stretching speeds contradicts to the theory of this phenomenon. The instability of the neck propagation was explained by the deformation softening of the polymer.

A comparison of hemiarthroplasty with total hip replacement for displaced fracture of femoral neck in the elderly

A comparison of hemiarthroplasty with total hip replacement for displaced fracture of femoral neck in the elderly - IJOS- Print ISSN No: - 2395-1354 Online ISSN No:- 2395-1362 Article DOI No:- 10.18231/j.ijos.2019.009, Indian Journal of Orthopaedics Surgery-Indian J Orthop Surg

Microstructural control and layer continuity in deformation bonding of metallic laminated composites

An experimental and simulation study is carried out to investigate the microstructure and tensile behavior of the roll-bonded metallic laminated composites incorporating a single hard layer. To control the microstructure, the effect of the hard layer thickness, hard layer material and layer sequence on the layer continuity is investigated in term of the strain partitioning, degree of necking and strain amplification factor. It is found that at low strain regimes, the thickness reduction of different layers is almost identical and the strain is partitioned equally between the layers. At high strain regimes, depending on the thickness and hardness ratio, unstable necks and rupture occur in the hard layer that lead to the strain partitioning between the constituent layers and cause the deformation to be inhomogeneous. Generally, the strain partitioning, degree of necking and strain amplification factor increase with decreasing the thickness ratio and increasing the hardness ratio. Results show that these parameters are affected by changing the layer sequence. Tensile test results reveal that the tensile strength of the fragmented structure is higher than that of the layered or continuous structure. In all cases, the experimental and simulation results are in a good agreement.

Fixation of Unstable Femoral Neck Fractures in Adults, Review Article

Background? Femoral neck fracture is a common problem especially in young adults. There are different methods of fixation of unstable femoral neck fractures in adults, some of which are accompanied by complications. Aim of Study: A systematic review on the different methods of fixation of unstable femoral neck fractures in adults with clarifying the incidence of nonunion, avascular necrosis, displacement and other complications in each type of fixation. Methods? A systematic review of literature was conducted on twelve studies (556 patients) published in literature using different methods of fixation with inclusion criteria including? English literature, human studies on adults aged 18-70 years with unstable neck of femur fractures Pauwel grade 3. Exclusion criteria including? in vitro studies, pathological and nonunited fractures in people aged below 18 or above 70 years with stable neck femur fractures Pauwel grade 1,2. Results: Targon femoral neck device had been provided to achieve highest rate of union with less complications than other methods of fixation but further evaluation of this device should be done within multiple studies in the future.Primary valgus osteotomy achieved a high union rate but still carries some complications especially delayed osteotomy site healing,coxa vara if improper reduction or fixation in addition to that it?s technically demanding and needs special surgical skills.Medial buttress plate augmentation should be studied more and more in further studies with longer follow up periods and larger number of patients Conclusion: Targon femoral neck device had been provided to achieve highest rate of union with less complications than other methods of fixation but further evaluation of this device should be done within multiple studies in the future. Keywords

Fixation of Unstable Neck Femur Fractures in Adults : Review Article

Background ː Femoral neck fracture is a common problem especially in young adults. There are different methods of fixation of unstable neck femur fractures in adults, some of which are accompanied by complications. Aim of study: A systematic review on the different methods of fixation of unstable femoral neck fractures in adults with clarifying the incidence of nonunion, avascular necrosis, displacement and other complications in each type of fixation. Methods ː A systematic review of literatures was conducted on five studies (306 patients ) published in literature in the last 10 years using different methods of fixation with inclusion criteria including ː English literature, human studies on adults aged 18-60 years with unstable neck femur fractures Pauwel grade 3. Exclusion criteria including ːin vitro studies, pathological and non united fractures in people aged below 18 or above 60 years with stable neck femur fractures Pauwel grade 1,2 Results: showed that Achieved union in management by osteosynthesis and primary valgus intertrochntric osteotomy using broad DCP showed better results than by other methods of fixation (cannulated screws , DCS, cephalomedullary nail) and by achieving union percentage of 92,7% as in (MP Singh 2008), the same percentage achieved by fixation by DHS as in (Frank Liporace 2008), followed by 92% rate of union achieved by fixed angle device (DCS or cephalomedullary nail) in (Frank Liporace 2008) Comparing complications in different fixation methods showed that complications are inevitable yet manageable, but higher complications rate associated with fixation of neck femur fractures using DHS by achieving 26,4% rate of nonunion and 26,4% rate of AVN in (carlos Roberto schwartsmann 2017) while rate of non union was 7,3% in valgus intertrochntric osteotomy by broad DCP and rate of AVN was 11% as in (MP Singh 2008). Summary and conclusion Management of unstable neck femur fractures in adults is done by means of direct fixation with cannulated screws, DHS, fixed angle device (DCS or cephalomedullary nail) or osteosynthesis and valgus intertrochntric osteotomy to avoid some adverse effects of the direct fixation methods, so,recent studies showed that valgus intertrochntric osteotomy achieve better results than traditional methods with less complications.

Treatment of displaced intracapsular neck fractures in active elderly patient: A Prospective overview of Osteosynthesis versus Prosthesis in 46 patients

Introduction: This paper determines if Osteosynthesis or Prosthesis replacement should be the treatment of choice, in active elderly patient with unstable intracapsular neck femur fracture. Material and Methods: A prospective analysis of the results of 46 patients that were performed in Pt. J.N.M. Medical College and associated Dr. B.R.A.M. Hospital Raipur (C.G.) over a period of 2 year was undertaken. The minimum period of follow-up was 2 years. Results: Out of these 46, 31 patients were treated with internal fixation (Richard’s compressive hip screw with supplementary cancellous screw fixation) and 15 patients were treated with Hemiarthroplasty (Austin Moore Unipolar Endoprosthesis). Overall, the average age of patients was 62.5 years. The mean age for internal fixation was 59 years and that of Hemiarthroplasty was 66 years. 61% of the patients were between 55-65 years of age group. Overall 29 patient (63%) were male and 17 patient were female (37%).Union occurred in 89% of cases in internal fixation. Overall, the functional outcome in internal fixation group was satisfactory with excellent/ good result found in 78% of cases, while in Hemiarthroplasty group it was 63%. Osteosynthesis group has less complication rate like pain, infection, fracture of shaft of femur, shortening and mortality than Hemiarthroplasty group. Conclusion: Osteosynthesis is justified as a primary treatment of intracapsular hip fracture even in displaced type in active elderly patient aged 55-65 years. Prosthesis replacement should be used in cases where neck is absorbed, in failed Osteosynthesis and in Non-union. Keywords: Neck femur, Elderly, Osteosynthesis, Prosthesis

Tensile elongation of unidirectional or laminated composites combining a brittle reinforcement with a ductile strain and strain-rate hardening matrix

We use the long-wavelength model of Hutchinson and Neale (1977) and Ghosh (1977) to estimate the uniform tensile elongation of two-phase composites deforming quasistatically according to the equistrain rule of mixtures, in which one phase is ductile while the other fractures progressively according to two-parameter Weibull statistics. We use shear-lag models in the literature to quantify load transfer from the ductile phase to the fractured brittle phase, and to estimate the influence of matrix strain and strain-rate hardening, of brittle phase fracture characteristics, and of phase volume and strength ratios, on the composite strain to failure as dictated by the onset of unstable necking. Calculations show that strain and strain-rate hardening of the ductile phase do relatively little to increase the ductility of the composite. Two parameters play a dominant role, namely the brittle-phase Weibull modulus and a dimensionless parameter describing load transfer across the two phases. The main practical implication of this analysis is that, to produce reasonably ductile two-phase composites, the best strategy is to aim for small layer thicknesses.

Fracture behavior of boehmite‐filled polypropylene block copolymer nanocomposites as assessed by the essential work of fracture concept

ABSTRACTThe essential work of fracture (EWF) method was adapted to determine the fracture toughness of poly(propylene‐block‐ethylene) (EPBC) based nanocomposites with different amounts (from 0 up to 5 wt %) of synthetic boehmite alumina (BA). The dispersion of BA in the matrix was studied by transmission and scanning electron microscopies. Agglomerated micronscale along with well dispersed nanoscale BA particles were present in the EPBC matrix. By contrast to the neat EPBC, all nanocomposites failed by unstable necking. Therefore the energy partitioning concept of the EWF was adapted and attention paid to the yielding‐related term. Both specific yielding‐related essential and nonessential work of fracture parameters increased linearly with the product of the yield stress and elongation at yield derived from static tensile tests. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40447.

Time Dependent FLC Determination Comparison of Different Algorithms to Detect the Onset of Unstable Necking before Fracture

The ISO standard 12004-2:2008E for the determination of forming limit curves based on the section method was approved in 2008. About 4 years of measuring experience in different laboratories has shown advantages and weaknesses of the standard and is leading to some minor changes in the specification. In the years from the development of this standard until today a further technical development of the optical measuring devices occurred, so that it is now possible to determine forming limit curves using the time history of the test. This procedure of determination is referred to a time dependent technique and could be the basis of the ISO 12004 part 2 proposal worked out by the work group Erweiterung FLC ISO 12004 of the German group of the IDDRG. This publication recapitulates existing work which was carried out from the IDDRG work group regarding the determination of forming limit curves for sheet metal materials. On one hand known issues with the current section based approach are discussed and on the other hand it deals with a comparison of different algorithms to determine the FLC from the time history of the Nakajima test using strategies to identify the instant of onset of instable necking. The different time dependent algorithms [ utilised are automatically selecting the area where necking is leading to fracture and then analyze the time history of such points using the first or the second time derivative of the true major strain, or of the true thinning strain using methods like: correlation coefficient (modified method based on [2]), gliding correlation coefficient, linear best fit (modified method based on [3]) and gliding difference of mean to median. The resulting experimental FLC points are compared with the results from the section technique described in ISO 12004 part 2 and with the maximum strain values measured in each test. Further a large number of forming limit curves were determined and used for a comparison of these different methods to define the most promising time dependent algorithm, which was selected as a suggestion for the working group defining the new proposed ISO standard 12004 part 2.

Le glottiscope AWS-Pentax™, alternative à la fibroscopie dans deux cas d’intubation difficile prévue du brûlé grave

Intubating patients with facial burn is difficult to most anesthesiologists. Awake flexible fiberoptic intubation is the gold standard for management of anticipated difficult tracheal intubation. However, serious facial burn and dysmorphic syndrome can make fiberoptic intubation more difficult or impossible. We report the use of awake oral intubation using the Pentax-Airway Scope (AWS) in two major burn patients with facial injury, in whom awake fiberoptic intubation was impossible. As shown in morbidly obese patient and in patients with unstable necks, AWS could be useful to facilitate tracheal intubation in awake, facial burn patients presenting with a potentially difficult airway. Awake AWS intubation seems as a potential alternative to awake fiberoptic intubation.

Pentax-AWS videolaryngoscope for nasotracheal intubation in patients with difficult airways

Pentax-AWS videolaryngoscope for nasotracheal intubation in patients with difficult airways

Management of Residual and Recurrent Aneurysms After Initial Endovascular Treatment

Coil instability possibly translating into higher delayed rebleeding rates remains a concern in the endovascular management of cerebral aneurysms. To report on 127 patients with endovascular aneurysmal remnants who underwent re-treatment over an 18 year period. Patients presenting with aneurysm residuals >20% of the original lesion, unstable neck remnants, aneurysmal regrowth, or new aneurysmal daughter sacs were treated by an individualized approach, using both endovascular and surgical techniques. Seventy-five aneurysmal remnants (59.1%) were treated by further re-embolization. Standard coil embolization was used in 65 cases, stent-protected coiling in 9 cases, and balloon remodeled coiling in 1 case, respectively. Fifty-two (40.9%) aneurysmal remnants were treated surgically. Standard microsurgical clipping was used in 44 patients, parent artery occlusion or trapping under bypass protection in 5 cases, deliberate clipping of the basilar artery trunk in 2 cases, and aneurysm wrapping in one case, respectively. Mechanisms of aneurysm recurrence were coil compaction in 93 cases and regrowth in 34 cases. A single reembolization was sufficient to occlude 78.7% of recurrences from coil compaction, but only 14.3% of recurrences from aneurysm regrowth. The individualized approach resulted in complete occlusion of 114 aneurysms (89.7%), with neck remnants and residual aneurysms detectable in 11 (8.7%) and 2 (1.6%) cases, respectively. Treatment morbidity was 11.9%, without significant differences between surgical (15.6%) and endovascular (9.3%) patients (P = .09). Recurrences from coil compaction were safely treated by re-embolization, whereas recurrences from aneurysmal regrowth may best be managed surgically when technically feasible.

A Microscopic Model of the Asymmetric Neck Growth during Sintering Process upon the Asymmetric Particle Arrangement

A kinetic Potts Monte Carlo model was used to investigate the microstructural evolution of a three particles configuration during sintering. The a series of peculiar phenomena was observed and analyzed quantitatively, which indicated that even if the particle shape and the contact area are both completely symmetrical, the asymmetric neck growth will arise due to a special particle arrangement. Although the linear relationship between neck size logarithm and time logarithm was consistent with the traditional theory, a slower neck growth rate comparing with that of the two sphere model displayed a result of the asymmetric neck growth. The analysis of the particle rotation was made to confirm the occurrence of the asymmetric neck growth. It was firstly observed that the morphology of the grain boundaries became bevel, and the reason for this morphology was discussed. All the special phenomena have proved that the asymmetric particle arrangement about the contact area can trigger the unstable neck growth.