Residual Compression Research Articles

Damage tolerance characterization of carbon fiber composites at a component level: A thermoset carbon fiber composite

This work focuses on the impact damage evaluation of a carbon fiber-reinforced thermoset composite at a component level (beams) as an effort to develop the service strategies for this class of materials. The beams were impact damaged at a variety of energy levels, and the pulse thermography nondestructive evaluation approach was used to characterize the damaged areas. The damaged beams were subjected to compression tests to evaluate their residual properties. As expected, both the beam maximum load and residual stiffness decreased with the increase in damage size. The damage growth rates under different load levels were investigated in fully reversed torsional fatigue tests. The fatigued beams were also characterized for their residual compression properties, which were then compared with those of the unfatigued beams. The results will be used to develop computer-aided engineering models to predict the residual strength and fatigue life of damaged composite components.

Residual Spinal Cord Compression Following Hemilaminectomy and Mini-Hemilaminectomy in Dogs: A Prospective Randomized Study.

The aim of this study was to compare the reduction of spinal cord compression after surgical treatment of dogs with acute thoracolumbar intervertebral disc (IVD) extrusion achieved using hemilaminectomy versus mini-hemilaminectomy techniques. This was a prospective randomized study with client-owned dogs presented with acute IVD extrusion that were allocated to surgical treatment using hemilaminectomy (n = 15) or mini-hemilaminectomy (n = 15) techniques. Plain and intravenous-contrast computed tomography was performed pre- and postoperatively. The preoperative minimal cross-sectional dimension of the spinal cord (MDSCpre) and the postoperative minimal cross-sectional dimension of the spinal cord (MDSCpost) were measured at the level of greatest compression. The minimal diameter of the uncompressed spinal cord was measured in a similar way both pre- (MDUSCpre) and postoperatively (MDUSCpost). Dogs in the mini-hemilaminectomy group had significantly greater reduction of compression (RC) (p < 0.01) after surgery compared to dogs in the hemilaminectomy group. The mean RC in the hemilaminectomy group was 34.6% and in the mini-hemilaminectomy group 62.6%. Our results showed a significantly greater reduction of spinal cord compression for mini-hemilaminectomy compared to hemilaminectomy. Additionally, mini-hemilaminectomy could be a preferred method due to its minimal invasiveness and easier access to lateral fenestration.

Residual strength evaluation after impact tests in extreme temperature conditions. New equipment for CAI tests

Abstract A large experimental campaign has included low velocity falling weight tests at room and low temperatures, on carbon fibre laminates in vinylester resin, clamped following the EN6038 or ASTMD7136 Standards, or simply supported by a water pillow. The latter clamping device was used to differently distribute the load and to investigate about the influence of the water backing. The mechanics-based understanding of the fluid-structure interaction occurring during the impact, was devoted to understand the role of water-backing on the loading experienced by the panel, toward informing the interpretation of empirical observations and design of new experiments. Non destructive and destructive evaluations for damage investigations were carried out whereas the design and the production of a new, more simple and reliable Compression After Impact (CAI) apparatus, was described and adopted to avoid errors due to misalignment between the applied load and the specimen. CAI tests were then, performed to evaluate the residual compression strength. Analytical and semi empirical models were evaluated and validated to predict the influence of the geometric parameters on the impact behaviour of the laminates. The final aim was to predict the impact energy, delamination and residual strength, in the different test conditions.

Causal analysis and management strategies of 30-day unplanned revision surgery following single-stage posterior vertebral column resection for severe spinal deformity

Objective: To investigate the causes of 30-day unplanned revision surgery following one-stage posterior vertebral column resection (PVCR) for severe spinal deformity and the methods of prevention and management. Methods: A total of 112 severe deformity patients underwent one-stage PVCR for surgical treatment in the 306(th) Hospital of People's Liberation Army from May 2010 to December 2015 were retrospectively reviewed. Six patients required reoperation within 30 days after PVCR, including 2 males and 4 females with average age of 21 years (ranging from 12 to 38 years). Four cases were congenital kyphoscoliosis, 1 was post-laminectomy kyphoscoliosis and 1 was post-tuberculous angular kyphosis. Three cases associated with preoperative neurologic deficit (Frankel C in 1 patient and D in 2 patients). The causes, management and outcomes of unplanned revision surgery within 30 days after PVCR were recorded. Results: The total incidence of unplanned revision surgery within 30 days following PVCR was 5.4% (6/112). There was 1 case due to cerebrospinal fluid leak, 5 cases with varying degrees of new neurologic deficits, the causes were as followed: dural buckling in 1 case, residual bone compression in 1 case, epidural hematoma compression in 2 cases, spinal subdural hematoma in 1 case. All the 6 cases underwent surgical exploration again, including further dural repair, decompression and hematoma clearance. After unplanned reoperation, 6 cases recovered completely. The average follow-up time after surgery was 30.8 months (ranging from 10 to 60 months). The major curve at coronal plane was improved from preoperative 87.7° to 34.2°, with a mean correction of 61.0% at final follow-up; the sagittal kyphosis curve was improved from preoperative 119.5° to 45.5°, with a mean correction of 61.9% at final follow-up. Two patients' neurological status improved from Frankel D to Frankel E, one patient's neurological status improved from Frankel C to Frankel E. Conclusions: One-stage PVCR could be an effective method for treatment of severe spinal deformity. The causes of 30-day unplanned reoperation after PVCR are as followed: cerebrospinal fluid leak, dural buckling, residual bone compression and hematoma compression. Timely surgical exploration can gain good clinical outcomes.

ЭКСПЕРИМЕНТАЛЬНО-ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ ДЕФОРМИРОВАНИЯ МЕТАЛЛИЧЕСКИХ ПЛЕТЕНЫХ СЕТОК ПРИ КВАЗИСТАТИЧЕСКОМ НАГРУЖЕНИИ

The results are presented of experimentally investigating tension of gas-impermeable packages of woven metal grids formed by freely stacking up grid layers, maintaining the orientation of the wires. The results of experimentally studying tension of grid packages in the direction of wires show that their pre-cogging normally to the grid layers produces a considerable effect - it increases the tensile strength of the pre-cogged package. This effect can be observed even in a single grid layer. To identify the mechanism of this increase, cogging and tension of a single grid layer is numerically modeled in a 3D-formulation. Based on the results of numerical modeling it is found out that in the cross-sections of the wires large zones of residual compression stresses are present, which result in increasing the tensile strength of the specimen in the layer plane. Keywords: woven grid, orthotropy, static compression, tension, non-linearity, elasto-plasticity, numerical modeling, experiment, contact, finite element method.

2,400 MPa급 고강도 강연선이 적용된 LNG 저장탱크의 프리스트레싱 효과

최근 국내에서는 고강도 강연선이 실구조물에 적용되는 사례가 늘어나고 있다. 이 연구에서는 LNG 저장탱크에 통상적으로 적용되는 1,860 MPa급 강연선을 2,400 MPa급 고강도 강연선으로 대체할 때 쉬스 배치 간격 증가에 따른 구조적인 영향을 고찰해 보았다. 먼저, LNG 탱크의 원통형 벽체를 모사하는 유한요소모델에 원환텐던 및 수직텐던의 프리스트레싱 효과를 등가하중으로 가하되 프리스트레싱 효과의 총합은 일정한 상태에서 텐던의 간격 및 긴장력을 조절한 결과, 고강도 강연선을 적용해도 설계 시 요구되는 소정의 응력 분포를 구현할 수 있는 것으로 나타났다. 또한, LNG 탱크 벽체 일부분을 모사하는 실대형 실험체를 제작하고 15.2 mm 직경 고강도 강연선이 31개 삽입된 쉬스를 2개 배치하여 매우 높은 수준의 프리스트레싱 힘이 콘크리트에 적절히 전달되는지 관찰하였다. 한편, 세계 최대 용량인 270,000 kl급 LNG 탱크의 유한요소모델을 구축하고 고강도 강연선을 적용했을 때의 프리스트레싱 효과를 일반 강연선의 경우와 비교하였으며, LNG 누출 사고 시에도 여유압축응력 및 여유압축구간과 같은 수밀성 규정을 만족함을 확인하였다. 이 연구결과는 2,400 MPa급 고강도 강연선이 실제 LNG 탱크에 적용될 때 유용하게 활용될 것으로 기대된다. High-strength strands have been increasingly applied to recent actual structures in Korea. Structural effect of the increased spacing of sheaths was investigated in this study when the usual 1,860 MPa strands of an LNG storage tank are replaced with 2,400 MPa high-strength strands. First, finite element models of a cylindrical wall of an LNG tank were established and prestressing effect of the circumferential and vertical tendons was considered as equivalent loads. As a result of varying the tendon spacing and prestressing force with the total prestressing effect kept the same, the stress distribution required in design was obtained with the high-strength strands. Also, a full-scale specimen that corresponds to a part of an LNG tank wall was fabricated with 31 high-strength strands with 15.2 mm diameter inserted in each of two sheaths. It was observed that such a high level of prestressing force can be properly transferred to concrete. Moreover, an LNG tank with the world's largest 270,000 kl capacity was modeled and the prestressing effect of high-strength strands was compared with that of normal strands. The watertightness specifications such as residual compressive stress and residual compression zone were also ensured in case of leakage accident. The results of this study can be effectively used when the 2,400 MPa high-strength strands are applied to actual LNG tanks.

A comparison of the effects of traditional shot peening and micro-shot peening on the scuffing resistance of carburized and quenched gear steel

Carburized and quenched specimens of 17CrNiMo6 gear steel were given two different shot peening treatments. Post-treatment Vickers hardness, residual stress, roughness and topography were determined. Traditional shot peening can increase surface hardness, residual stress and roughness. By contrast, micro-shot peening can decrease of surface roughness and increase both the surface hardness and residual stress even more. Scuffing tests were carried out using a ring-in-V-notch test configuration. It was found that shot peening can improve the scuffing resistance properties of gear steel, and that a combination of traditional shot peening and micro-shot peening can improve the scuffing resistance of carburized and quenched gear steel to the largest degree. The hardness and residual compress stress, roughness and topography produced during shot peening have an effect on the scuffing resistance of the carburized and quenched gear steel.

Calcareous and granite aggregate concretes after fire

This paper presents the results of an experimental research on the assessment of the residual mechanical properties of calcareous and granite aggregate concretes after fire. The influence of the following parameters was tested: the loading level (0.3 and 0.7fcd); the cooling process (cooling in the air and by water jet) and the maximum temperature that the concrete was subjected to (20, 300, 500 and 700°C). The mechanical properties studied were the residual compression, direct and splitting tensile and flexural strengths, modulus of elasticity and Poisson's ratio. The results showed in general that the higher the temperature and faster the cooling process is, as the one by water jet, the higher the negative impact on the residual mechanical properties of the concrete is, being the strength nearly null for above 600°C.

Finite element analysis of CFRP laminates subjected to compression after edge impact

Composite structures are particularly vulnerable to impact which lowers drastically theirs residual strength. In particular, the edge impact on composite stiffener is known as a critical factor on the loss of residual compression strength. Then it is necessary to develop a model able to simulate impact and compression after impact in order to numerically optimize composite structures within impact damage tolerance.In the present paper, a unique model, based on Discrete Ply Model, allows to simulate edge impact and compression after impact (CAEI) of two stacking sequences highly oriented, representative of a real aeronautical stiffener structure. A relatively good correlation is found between experiment and model regarding the important number of phenomena which is taken into account: permanent indentation after impact, force–displacement impact curve, crack length after impact, delamination after impact, stress-displacement CAEI curve, stress-out-of-plane displacement curve, CAEI final failure. Moreover only 14 parameters are needed to feed this model, and all are obtained using standard tests and have physical relevance. This concept is important because it allows considering running similar tests with other materials without performing complex and special identification tests but only using physical parameters of standard tests. The good results of this approach could allow to define a new design method to improve the edge impact damage tolerance.

Experimental analysis of CFRP laminates subjected to compression after edge impact

Composite structures are particularly vulnerable to impact which lowers drastically theirs residual strength. In particular, the edge impact on composite stiffener is known as a critical factor on the loss of residual compression strength. At the same time, manufacturing of stiffened panels and achievement of experimental tests, of edge impact and compression after edge impact (CAEI) with stiffened panel, are particularly complex and costly. Then an experimental test set up has been designed to easily study the edge impact and the CAEI without complex specimen. It avoids the complex manufacturing of stiffener panels and avoids the use of high capacity machine. The mean goal is to define a new design method to improve the edge impact damage tolerance.Then experimental analysis of CAEI has been carried out on carbon fibre reinforced plastic (CFRP) laminates. This paper presents these results in order to determine the residual properties of the structure and to elaborate the failure scenario. It seems that a propagation of a compressive fibre failure plays a major role in the mechanisms that drives the laminate residual strength after edge impact. The good agreement of an open hole model with point stress approach seems to confirm the major role of the compressive fibre failure in the final failure.

Residual strength and damage characterization of repaired glass/epoxy composite laminates using A.E. and D.I.C

In this paper, the effect of introducing different phases of fibre reinforcement in epoxy matrix at the dressed site in adhesively bonded external patch repair for damaged glass/epoxy composites under in-plane compressive loads was investigated. Three repair materials consisting of an epoxy matrix reinforced with either micro sized particulate fibres, chopped short fibres or continuous fibres were used in this study. Since this investigation extensively focuses on the effect of different types of fibre reinforcements on residual compression properties of repaired glass/epoxy composite laminates, the external patches were avoided. Acoustic emission (AE) and digital image correlation (DIC) were utilized to form qualitative and quantitative assessments of the damage progression profile. The compression results illustrate that reinforcing the epoxy adhesive material with glass fibres significantly increased the residual compression strength of repaired glass/epoxy composite specimens. In particular, the use of chopped fibre reinforced adhesive repair material improved the average residual compressive strength by 18.91% in comparison to the specimens conventionally repaired using neat epoxy resin.

Prediction of incomplete decompression after cervical laminoplasty on magnetic resonance imaging: The modified K-line

ObjectivesThe original K-line was developed on plain radiograph to predict incomplete indirect decompression for the patients with ossification of the posterior longitudinal ligament. The current study modified the K-line on magnetic resonance imaging (MRI) to determine risk factors for incomplete decompression after laminoplasty and to provide a guide for predicting incomplete decompression after laminoplasty and making decisions regarding the surgical approach in patients with cervical spondylotic myelopathy (CSM). Patients and methodsA retrospective review of 47 patients with CSM after laminoplasty was conducted. The modified K-line was defined as a line connecting both anterior points of the spinal cord at the level of the inferior vertebrae endplates of C2 and C7 on sagittal T1-weighted MR image. Quantitative analysis of the interval between the maximal anterior compression factor and the modified K-line (IAK) was performed to investigate the efficiency and practicality of this modified K-line. Data analysis involved logistic regression and Spearman rank correlation coefficient. ResultsThirteen patients (27.7%) had postoperative residual anterior compression of the spinal cord (ACS). Univariate logistic regression with backward stepwise procedure showed that only IAK (odds ratio: 0.301; 95% confidence interval: 0.134–0.673, P=0.003) was a significant risk factor for the occurrence of postoperative ACS. Incidence of ACS was 80% in patients with an IAK of less than 1.5mm and 96.2% in those whose IAK is 0mm. ConclusionThe modified k-line can provide a guide for predicting poor clinical outcome after laminoplasty and making decisions regarding the surgical approach in patients with CSM.

A Study on Residual Compression Behavior of Structural Fiber Reinforced Concrete Exposed to Moderate Temperature Using Digital Image Correlation

Fire ranks high among the potential risks faced by most buildings and structures. A full understanding of temperature effects on fiber reinforced concrete is still lacking. This investigation focuses on the study of the residual compressive strength, stress strain behavior and surface cracking of structural polypropylene fiber-reinforced concrete subjected to temperatures up to 300 °C. A total of 48 cubes was cast with different fiber dosages and tested under compression after exposing to different temperatures. Concrete cubes with varying macro (structural) fiber dosages were exposed to different temperatures and tested to observe the stress–strain behavior. Digital image correlation, an advanced non-contacting method was used for measuring the strain. Trends in the relative residual strengths with respect to different fiber dosages indicate an improvement up to 15 % in the ultimate compressive strengths at all exposure temperatures. The stress–strain curves show an improvement in post peak behavior with increasing fiber dosage at all exposure temperatures considered in this study.

Repeated 3.0 Tesla Magnetic Resonance Imaging After Clinically Successful Lumbar Disc Surgery.

Prospective cohort study. To describe the naturally occurring magnetic resonance imaging (MRI) findings after successful microsurgical removal of lumbar disc herniation with repeated MRI examinations. The interpretation of MRI after spinal surgery may be particularly challenging and image findings do not always correlate to clinical findings. Early postoperative MRI has limited value in the evaluation of patients after surgery for lumbar disc herniation. Prospective study of 30 successfully operated patients, which underwent 3.0 T MRI within 24 h after surgery for lumbar disc herniation and repeated at 6 weeks and 3 months postoperatively. Postoperative image findings (nerve root enhancement, nerve root thickening, displacement or compression of the nerve root, and residual mass size and signal) were assessed quantitatively. Inter-rater reliability was tested. Inter-rater reliability between neuroradiologists was moderate for assessed MRI variables. In the immediate postoperative phase, compression or dislocation of the nerve root at the operated level was common. A residual mass at the operated level was seen in 80%, 47%, and 33% after 24 h, 6 weeks, and 3 months, respectively. Postoperative dislocation or compression of the nerve root from residual masses was seen in 67%, 24%, and 14% after 24 h, 6 weeks, and 3 months, respectively. A residual mass with a higher signal than muscle on T2-weighted images was seen in 80%, 30%, and 17% after 24 h, 6 weeks, and 3 months, respectively. A residual mass with compression or dislocation of the nerve root at the operated level, that disappears over 3 months, is a common MRI finding in patients successfully operated for symptomatic lumbar disc herniation. An expectant approach instead of early reoperations may perhaps be preferred in patients with residual pain and root compression due to residual masses with high T2-signal since these often seem to resolve spontaneously. 3.

Cervical ossification of the posterior longitudinal ligament: factors affecting the effect of posterior decompression

Objective: Decompression procedures for cervical myelopathy of ossification of the posterior longitudinal ligament (OPLL) are anterior decompression with fusion, laminoplasty, and posterior decompression with fusion. Preoperative and postoperative stress analyses were performed for compression from hill-shaped cervical OPLL using 3-dimensional finite element method (FEM) spinal cord models.Methods: Three FEM models of vertebral arch, OPLL, and spinal cord were used to develop preoperative compression models of the spinal cord to which 10%, 20%, and 30% compression was applied; a posterior compression with fusion model of the posteriorly shifted vertebral arch; an advanced kyphosis model following posterior decompression with the spinal cord stretched in the kyphotic direction; and a combined model of advanced kyphosis following posterior decompression and intervertebral mobility. The combined model had discontinuity in the middle of OPLL, assuming the presence of residual intervertebral mobility at the level of maximum cord compression, and the spinal cord was mobile according to flexion of vertebral bodies by 5°, 10°, and 15°.Results: In the preoperative compression model, intraspinal stress increased as compression increased. In the posterior decompression with fusion model, intraspinal stress decreased, but partially persisted under 30% compression. In the advanced kyphosis model, intraspinal stress increased again. As anterior compression was higher, the stress increased more. In the advanced kyphosis + intervertebral mobility model, intraspinal stress increased more than in the only advanced kyphosis model following decompression. Intraspinal stress increased more as intervertebral mobility increased.Conclusion: In high residual compression or instability after posterior decompression, anterior decompression with fusion or posterior decompression with instrumented fusion should be considered.

Improved durability of cement mortars exposed to external sulfate attack: The role of nano & micro additives

External sulfate attack (ESA) is a critical issue which may turn into a big concern about the durability and service life of structural elements get into contact with high sulfate environments. Especially when improper concrete mixture materials and design parameters are selected, structural elements exposed to sulfate attack might be significantly deteriorated. In this experimental work, the effects of various micro and nano cementitious materials on the long-term durability of mortars against ESA were studied. For this purpose, nano (colloidal) silica (NS), micro silica (MS), fly ash (FA) and ground granulated blast-furnace slag (GGBS) were selected with various replacement ratios. All the samples were kept in 5% sodium sulfate solution for approximately 3 years and the expansions caused by sulfate attack were monitored. Additionally, at the end of 3 years of exposure, residual flexural strength, compression strength and ultrasonic pulse velocity (UPV) of mortars were determined and their results were compared with the reference samples which do not contain mineral additives and cured in water. For the micro-structural evaluations, XRD analysis was performed. Results have shown that significant improvement against sulfate attack was achieved by using the additives mentioned above by properly selecting its dosage. Within the limits of this work, mineralogical analysis via XRD tests have proved that decomposition of the sulfate exposed reference samples which do not contain any mineral additives was not caused by ettringite formation, but gypsum formation.

The Influence of Cochlear Mechanical Dysfunction, Temporal Processing Deficits, and Age on the Intelligibility of Audible Speech in Noise for Hearing-Impaired Listeners.

The aim of this study was to assess the relative importance of cochlear mechanical dysfunction, temporal processing deficits, and age on the ability of hearing-impaired listeners to understand speech in noisy backgrounds. Sixty-eight listeners took part in the study. They were provided with linear, frequency-specific amplification to compensate for their audiometric losses, and intelligibility was assessed for speech-shaped noise (SSN) and a time-reversed two-talker masker (R2TM). Behavioral estimates of cochlear gain loss and residual compression were available from a previous study and were used as indicators of cochlear mechanical dysfunction. Temporal processing abilities were assessed using frequency modulation detection thresholds. Age, audiometric thresholds, and the difference between audiometric threshold and cochlear gain loss were also included in the analyses. Stepwise multiple linear regression models were used to assess the relative importance of the various factors for intelligibility. Results showed that (a) cochlear gain loss was unrelated to intelligibility, (b) residual cochlear compression was related to intelligibility in SSN but not in a R2TM, (c) temporal processing was strongly related to intelligibility in a R2TM and much less so in SSN, and (d) age per se impaired intelligibility. In summary, all factors affected intelligibility, but their relative importance varied across maskers.

Craniovertebral junction anomalies: When is resurgery required?

Craniovertebral junction (CVJ) abnormalities, such as atlantoaxial dislocation (AAD) with or without basilar invagination (BI), with or without associated Chiari malformation (CM), may cause a high cervical myelopathy. Occasionally, mechanical factors such as inadequate canal decompression, torticollis, and/or scoliosis may lead to lack of improvement following the primary surgery. Furthermore, implant-related factors, requiring implant revision/removal, or the presence of surgical site infections may cause the patient to undergo resurgery. This study was aimed at highlighting the underlying etiopathogenesis of resurgery following the primary surgery undertaken in CVJ abnormalities. This was a retrospective study from a tertiary care referral institute focusing on 414 operated cases of CVJ anomalies. The data of 55 patients who underwent resurgery included their clinicoradiological assessment and operative records. The inclusion criteria included failed primary procedure, repeat procedure for construct failure, infection at the surgical site, or wound dehiscence. Pure CM patients without bony anomalies were excluded from the study. A total of 137 procedures were performed in 55/414 (13%) patients. Causes of resurgery could be divided into ventral [redo or denovo transoral decompression (TOD) or wound-related complications, n = 33, 40.2%] and dorsal causes (implant-related factors/wound infections, n = 49, 59.8%). De novo TOD was done in persisting myelopathy following posterior fusion (PF) with C1-2 distraction (n = 15,18.3%,). Redo TOD was done for residual anterior bony compression [n = 8, 9.6%, OR 0.61; [CI = 0.20-1.86]. Causes for oral wound reexplorations (n = 10, 12.2%) included velopharyngeal insufficiency, wound resuturing, oral bleeding, and cerebrospinal fluid (CSF) leak. Dorsal causes included: (A) Implant factors (n = 27, 32.7%) and (B) neck wound reexplorations (n = 22, 26.8%). Presence of subaxial spine scoliosis, torticollis, and asymmetric joints increased the incidence of reexploration. Occipitocervical fusion rather than C1-2 fusion was more prone towards construct loosening. Patients undergoing distraction with PF may require transoral surgery due to persisting myelopathy, especially in the presence of torticollis, scoliosis, and symmetrical joints. Single stage TOD+PF increases the chances of implant infection due to tissue contamination, bacteremia, or transfacetal migration of microbes. Chronic/recurrent sinus is usually a harbinger of deeper infection and can be cured with implant removal.

Kommerell Diverticulum Should Be Removed in Children With Vascular Ring and Aberrant Left Subclavian Artery

Right aortic arch with aberrant left subclavian artery is the most frequent cause of vascular ring. Ligamentum arteriosus division opens the ring but leaves the Kommerell diverticulum in place, with a risk of residual compression, aneurysmal dilation, dissection, or even rupture. A procedure consisting of translocation of the aberrant left subclavian artery to the left carotid artery with removal of the Kommerell diverticulum and division of the ligamentum is currently advocated. Between September /2009 and August 2011, 12 consecutive patients underwent the foregoing procedure. Clinical findings, surgical procedure, complications, histopathologic findings, and follow-up data were retrospectively analyzed. Mean age at the time of operation was 7.7 years (median, 4.3 years, range, 0.9 to 18.9 years), and mean weight was 26 kg (median, 18 kg; range, 8.4 to 59 kg). All patients had symptoms. Computed tomography scan or magnetic resonance imaging, or both, had confirmed the diagnosis in all patients. Postoperative events, all transient, included chylothorax (1 patient), phrenic palsy (1 patient), pneumonia (1 patient), and the need for prolonged chest drainage (3 patients). Mean follow-up reached 19 months (median, 13 months; range, 12 to 41 months). Mild residual respiratory symptoms were noted in 3 patients. Echo-Doppler analysis showed a patent left subclavian-to-carotid artery anastomosis. Histopathologic analysis of the resected diverticulum (n = 6) showed cystic medial necrosis in four diverticula (focal in one). Translocation of the aberrant left subclavian artery with diverticulum resection and ligamentum division is an efficient procedure for symptom relief. Profound wall abnormalities such as medial necrosis in at least 50% of the analyzed diverticula encourage us to maintain this strategy, to reduce the risk of aneurysm formation and dissection.

Post-fire mechanical properties of sandwich composite structures

A thermal–mechanical model for calculating the residual stiffness and strength of fire-exposed sandwich composite structures is presented. The model computes the unsteady-state heat flow and decomposition of a sandwich composite exposed to one-sided radiant heating representative of a fire scenario. The model also computes the residual tension and compression properties of a fire-exposed sandwich composite at room temperature. The accuracy of the model is assessed using post-fire stiffness and failure stress property data for a sandwich composite beam consisting of face skins of E-glass/vinyl ester laminate and a core of balsa wood. Experimental testing reveals that the residual tension and compression properties of the sandwich composite decrease rapidly due mainly to thermal decomposition to the fire-exposed skin. It is demonstrated that the model can accurately predict the residual stiffness and strength properties of fire-exposed sandwich composites. The model reveals that the post-fire tension properties are controlled by char damage to the entire sandwich composite whereas the post-fire compression properties are only dependent on charring to the front skin, resulting in a more rapid loss in stiffness and strength than the tension properties.