Thick Ligament Research Articles

Morphological and morphometric analysis of oblique popliteal ligament in North Indian population: a cadaveric study.

To study the morphology and the morphometry of the oblique popliteal ligament (OPL). Thirty cadaver knees were dissected to study the morphology and morphometry of the OPL. For the measurement of the morphology of the OPL a standard tape and the vernier callipers were used. Out of 30 specimens 14 were Y shaped, 10 were band shaped, and 6 were Z shaped observed. Total length was measured on both the limbs, on the right side it was 4.5 ± 0.4cm and on the left side 4.5 ± 0.5cm was recorded. Width at the medial attachment was also measured on both the limbs, on the right side it was 4.6 ± 0.5cm and on the left side 4.7 ± 0.5cm was recorded. And width at the lateral attachment was recorded too, on the right side it was 4 ± 0.3cm and on the left side it was 4 ± 0.3cm. Width at the midpoint was recorded as on the right side 3.5 ± 0.2cm and on the left side 3.5 ± 0.2cm. The OPL is a thick ligament that arises as an extension of the semimembranosus, and it exists in various morphology which includes band, Y, Z, complex shapes.

Deformation and breakup of compound droplets in airflow

HypothesisImmiscible liquids are commonly used to achieve unique functions in many applications, where the breakup of compound droplets in airflow is an important process. Due to the existence of the liquid-liquid interface, compound droplets are expected to form different deformation and breakup morphologies compared with single-component droplets. ExperimentsWe investigate experimentally the deformation and breakup of compound droplets in airflow. The deformation characteristics of compound droplets are quantitatively analyzed and compared with single-component droplets. Theoretical models are proposed to analyze the transition between breakup morphologies. FindingsThe breakup modes of compound droplets are classified into shell retraction, shell breakup, and core-shell breakup based on the location where the breakup occurs. The comparison with single-component droplets reveals that the compound droplet is stretched more in the flow direction and expands less in the cross-flow direction, and these differences occur when the core of the compound droplet protrudes into the airflow. The transition conditions between different breakup modes are obtained theoretically. In addition, the eccentricity of the compound droplet can lead to the formation of the thick ligament or the two stamens in the droplet middle.

Comparison of ligamentum flavum thickness between central and lateral lesions in a patient with central lumbar spinal canal stenosis.

Thickened ligamentum flavum has been considered as a major cause of central lumbar spinal canal stenosis (CLSCS). Previous studies have demonstrated that ligamentum flavum thickness (LFT) is correlated with aging, degenerative spinal stenosis, and disc degeneration. Thus, hypertrophy of the ligamentum flavum is a major cause of CLSCS, and measurement of LFT has been considered a morphologic parameter in the diagnosis of CLSCS. To our knowledge, comparison of LFT between central and lateral lesions has not been reported. In addition, no research has analyzed best clinical cutoff values of central ligament flavum thickness (CLFT) and lateral ligament flavum thickness (LLFT). This study aimed to compare CLFT with LLFT in patients with CLSCS and further compare the CLFT and LLFT findings between the 2 groups to analyze LFT variation. Both CLFT and LLFT samples were collected from 101 participants with CLSCS and from 103 participants in the control group who underwent lumbar magnetic resonance imaging without evidence of CLSCS. Axial T2-weighted lumbar magnetic resonance scans were acquired at the L4 to 5 facet joint level from each participant. Average CLFT value was 2.25 ± 0.51 mm in the control group and 4.02 ± 0.74 mm in the CLSCS group. Average LLFT value was 2.50 ± 0.51 mm in the control group and 3.38 ± 0.66 mm in the CLSCS group. CLSCS patients had significantly higher CLFT and LLFT (both P < .001). Regarding the validity of both CLFT and LLFT as predictors of CLSCS, a receiver operating characteristic estimation revealed that the most suitable cutoff value for CLFT was 3.10 mm, with sensitivity of 95.0%, specificity of 94.2%, and an area under the curve of 0.97. The best cut-off value of LLFT was 2.92 mm, with sensitivity of 78.2%, specificity of 77.7%, and area under the curve of 0.87. We have 4 important new findings: The mean CLFT is significantly lower than that of the mean LLFT in the normal control group; CLFT and LLFT are both significantly associated with CLSCS; Increase rate of CLFT is faster than that of LLFT in the CLSCS group; and CLFT is a more sensitive measurement parameter to predict CLSCS than LLFT.

Characterization of Alar Ligament in Young Adult on 3.0T MRI: A Cross-sectional Study in IIUM Medical Centre, Kuantan

Introduction: Alar ligament is a paired craniocervical junction ligaments which stabilizes the atlantooccipital and atlantoaxial joints. The main purpose of the study was to compare the normal anatomy of alar ligament on MRI between male and female. The prevalence of alar ligament visualized on MRI and its characteristics were also studied apart from determining the association between the heights of respondents with alar ligament signal intensity and dimensions. Methods: Fifty healthy volunteers were studied using 3.0T MR scanner (Siemens Magnetom Spectra) by 2-mm proton density, T2 and fat-suppression sequences. Alar ligament visualization, dimensions and variability of the ligament courses, shapes and signal intensity characteristics were determined. Results: The orientation of the ligament was laterally ascending in most of the subjects (60%), predominantly oval in shaped (54%) and 67% showed inhomogenous signal. Females are 70% less likely to exhibit alar ligament signal inhomogeneity than males. There were positive correlation between height and the craniocaudal diameter of the alar ligament as well as the anteroposterior diameter, which were statistically significant (r = 0.25, n = 100, p = 0.01 and r = 0.201, n = 100, p = 0.045 respectively). Conclusion: Tremendous variability of alar ligament shows that clinical and multimodality correlation needs to be exercised, especially in evaluating alar ligament MR signal in male. Taller individuals otherwise tend to have longer and thicker ligaments. Future studies with larger samples of alar ligaments including trauma cases are also recommended to supplant a new classification system of alar ligament injury.

Effects of coal characteristics on the structure and performance of coal-based carbon foam prepared by self-foaming technique under atmospheric pressure

Carbon foams with open cell structure and high compressive strength were produced using three strongly caking bituminous coals without any pretreatment, by a proposed self-foaming technique under atmospheric pressure with the characteristics of simple operation, safety, and efficiency. The chemical composition, thermoplastic behavior, and pyrolysis characteristics of the raw coals were characterized by FT-IR, Raman, solid-state 13C NMR, Gieseler fluidity, Audibert-Arnu dilatation, and TG/DTG techniques. The results showed that the structure and mechanical properties of the carbon foams could be mainly controlled by fluidity and the chemical composition of the raw coals under the same initial foaming pressure. The carbon foams produced from DS coal with high fluidity and aliphatic carbon contents originated from the cyclic aliphatic structures presented open-cell structures, large cell size, andhigh porosity (78.43%) and showed a low compressive strength of 2.71 MPa. Carbon foam obtained from the TL coal with low fluidity, and large aromatic cluster structure presented thick ligaments, relatively uniform cell distribution and better crystalline structure, which showed the highest compressive strength of 18.13 MPa.

Evaluation of magnetic resonance imaging findings in adhesive capsulitis: which quantitative findings are most valuable?

This study aims to investigate magnetic resonance imaging (MRI) findings in adhesive capsulitis (AC) and determine the most valuable MRI finding in diagnosis using easily applied quantitative methods. Shoulder MRI was performed on 193 patients who were diagnosed with AC by clinical examination and 116 controls. Axillary pouch thickness (APT), superior and inferior glenohumeral ligament (SGHL and IGHL) thickness, coracohumeral ligament (CHL) thickness, fluid increase and soft-tissue thickness in the rotator interval (RI), and increases in the fluid and signal in the localization of biceps tendon attachment were evaluated. MRI examinations were assessed by three radiologists blinded to the clinical findings of the patients, and the results were obtained based on consensus and records. There were 119 women and 74 men in the AC group and 80 women and 36 men in the control group. IGHL, SGHL, RI, and CHL thicknesses were measured thicker in AC patients than in the control group. When IGHL=4, RI=3.6, SGHL=2.0, CHL=4.6-mm cutoff, the area under the receiver operating characteristic (ROC) curve (AUC) values were 0.700, 0.922, 0.972, and 0.783, respectively. According to the results obtained in this study, IGHL=4 mm, RI=3.6 mm, SGHL=2.0 mm, and CHL=4.6 mm can support the diagnosis of AC. Using the quantitative values in diagnosis can provide objective criteria and prevent variability among interpreters.

Mechanical Enhancement of Graded Nanoporous Structure

Abstract Inspired by the development of strong and ductile composite and gradient materials over the past decade, here, we report the investigation of a graded nanoporous (NP) structure utilizing molecular dynamics simulations. The structure is generated by inducing a gradient scaling parameter in a Gaussian random field model. It has a large ligament/pore size toward the core and a small ligament/pore size toward the surface. The redistribution of stress and strain under tensile loading is then scrutinized and compared between the functional graded NP structure and two conventional NP structures with identical relative density but constant ligament size. During loading, the thick ligaments in the gradient structure yield at high stress, leading to the entire structure's high mechanical strength. The thin ligaments help the structure accommodate significant plastic strain by promoting uniform deformation. Both parts of the gradient structure worked collectively and resulted in the structure exhibiting a synergy of excellent strength and good deformability.

Assessment of thickness of in vivo autograft tendons around the knee and its correlation with anthropometric data, thickness of patella and anterior cruciate ligament tibial foot print diameter.

Inadequate diameters of the autograft tendons are known to be a major cause of graft failure in ligament reconstruction. The purpose of the study was to measure the in-vivo thickness of the available autograft options around the knee and to seek a correlation between the thickness of the tendons and the anthropometric data, patellar thickness and anterior cruciate ligament (ACL) footprint sagittal diameter. Magnetic resonance imaging of 104 consecutive patients with suspected knee injuries were utilized for measurement of the in vivo thickness of pes anserinus tendon (diameter and cross-sectional area [CSA]), patellar tendon (PT) and quadriceps tendon (QT). Pearson’s coefficient was used to find out the relationship between the tendon thickness and anthropometric data, thickness of patella and ACL tibial foot print sagittal diameter. The mean diameters and CSA of the semitendinosus tendon (ST) and gracilis tendon (GT) were 3.77±0.49 mm, 11.62±1.62 mm2 and 2.87±0.27 mm, 6.64±1.18 mm2 respectively. QT and PT thicknesses were 7.36±0.87 mm and 4.50±0.62 mm respectively. Height and the patellar thickness were seen to have moderate correlation with ST and PT thickness. Weak correlation was seen between the other anthropometric variables and tendon thickness. Magnetic resonance imaging (MRI) assessment of tendon sizes is a reliable method with good inter and intra-rater agreement. Assessment of these anatomical structures with help of MRI would be helpful in preoperative planning and can help in identifying those patients at risk of having smaller tendons.

Eagle's syndrome: A case report of a 39-year-old male

Ossifying stylohyoid ligament can be seen accidently in panoramic images. Sometimes this status is asymptomatic. However, in the presence of symptoms such as pain in the pharynx, a foreign body sensation, tinnitus or otalgia it is called Eagle’s syndrome. The other symptoms due to the pressure on carotid artery including migraines, aphasia or vertigo and syncope especially in turning head to suffering side may be reported. This case was a thirty-nine-year-old man by thick ossified stylohyoid ligament in both sides along with five pseudoarticles together with a background of head and neckache specially in cold weather.

A concurrent high strength and ductility of 3D gyroidal nanoporous metallic glasses

By using molecular dynamics simulations, we investigate the tensile response of nanoporous (NP) Cu50Zr50 metallic glasses (MGs) with 3D gyroidal structure. Similar to nanoporous crystalline metals, NP–MGs fail by the plastic necking of ligaments, but shear bandings (SBs) prevail in those thick–ligament specimens. Particularly, with ligament diameter decreasing to 2.34 nm, SBs are hardly observed due to the limit of translation from shear transformation zones, resulting in superior strength and ductility of NP–MGs. The critical ligament size to suppress the formation of SBs is much smaller than those calculated value in MGs. The observations reveal a design strategy that a concurrent high strength and ductility of MGs could be obtained by designing 3D nanoporous structure with supra–nano size. The scaling laws for Young's modulus and strength as functions of relative density and ligament diameters are addressed, consistent with those in nanoporous crystalline materials.

In situ X-ray microtomography of the compression behaviour of eTPU bead foams with a unique graded structure

In situ X-ray microtomography was used to characterize the changes in internal structure of an expanded thermoplastic polyurethane (eTPU) bead foam used in footwear midsole during compression. Quantitative data on cell size and volume changes based on conventional segmentation were computed. Image correlation on the 4D datasets, i.e. a 3D tomogram collected at various points during deformation, was performed to map the strain fields to aid in analysis of observed deformation. Morphological and structural characterization revealed the gradient porosity and ligament thickness and its influence on the global mechanical behaviour of individual bead foam. The correlation of changes in void size and shape, identified areas of potentially weak regions. Strain maps derived by using voids as markers were adequate to capture the instabilities in local cell collapse. The smaller cells at the surface densified more readily providing more resistance to deformation. In addition, the thicker ligaments in the centre of the bead also aided resistance to deformation. Finally, our results showed the initiation of failure in cell structure was influenced by the heterogeneities around the immediate neighbours in a cluster of voids.

Unique myological changes associated with ossified fabellae: a femorofabellar ligament and systematic review of the double-headed popliteus.

IntroductionThe fabella is a sesamoid bone embedded in the tendon of the lateral head of the gastrocnemius. It is the only bone in the human body to increase in prevalence in the last 100 years. As the fabella can serve as an origin/insertion for muscles, tendons, and/or ligaments (e.g., the oblique popliteal and fabellofibular ligaments), temporal changes in fabella prevalence could lead to temporal changes in “standard” knee anatomy. The aim of this study was to investigate unique myological changes to the posterolateral corner knee associated with ossified fabella presence and perform a systematic review to contextualize our results.MethodsThirty-three fresh frozen cadaveric knees were considered. As the knees were all used for previous experimentation, the knees were in variable levels of preservation. Those with adequate preservation were used to determine ossified fabella presence/absence. When ossified fabellae were present, unique myologies associated with the fabella were recorded. A systematic review was performed on the double-headed popliteus to investigate possible correlations between this anatomical variant and the fabella.ResultsOf the 33 knees, 30 preserved enough soft tissue to determine fabella presence/absence: 16/30 knees had fabellae (five cartilaginous and 11 ossified). Eight of the eleven knees with ossified fabellae retained enough soft tissue to investigate the posterolateral knee anatomy. Of these, 4/8 exhibited unique myological changes. One knee had a double-headed popliteus muscle where one head originated from the medial side of a large, bulbous fabella. A systematic review revealed double-headed popliteus muscles are rare, but individuals are 3.7 times more likely to have a fabella if they have a double-headed popliteus. Another knee had a large, thick ligament stretching from the lateral edge of the fabella to the inferoposterior edge of the lateral femoral epicondyle, deep to the lateral collateral ligament (LCL) and near the popliteal sulcus. We found no mention of such a ligament in the literature and refer to it here as the “femorofabellar ligament”. In all four knees, the plantaris and lateral gastrocnemius appeared to share a common tendinous origin, and the fabella was located at/near the junction of these muscles. In the case of the double-headed popliteus, the fabella clearly served as an origin for the plantaris.ConclusionsDespite being found in an average of 36.80% of human knees, most standard anatomical models fail to account for the fabella and/or the unique myological changes associated with fabella presence. Although our sample is small, these data highlight aspects of human biological variability generally not considered when creating generalized anatomical models. Further work is needed to identify additional changes associated with ossified fabellae and the functional consequences of omitting these changes from models.

The ACL of the Ankle Joint: A Cadaveric Evaluation of the Subtalar Intrinsic Ligaments and Optimal Surgical Approach

Category:Ankle; Basic Sciences/Biologics; SportsIntroduction/Purpose:The biomechanics of ankle sprains involves a multiplanar-supination motion and not the strict inversion as is often described. During supination, calcaneal inversion occurs at the anatomic subtalar joint. The intrinsic subtalar ligaments include a series of broad thick ligaments situated in the tarsal canal that separate the anterior and posterior compartments. The subtalar intrinsic ligaments are damaged in an estimated 25% to 80% of all lateral ankle sprains. We hypothesize that the intrinsic subtalar ligaments have a multiplanar role in ankle joint stabilization similar to that of the anterior cruciate ligament at the knee. The purpose of this study is to evaluate the efficacy of four surgical approaches to the subtalar ligaments through cadaveric dissection.Methods:Four fresh-frozen cadaveric ankle specimens were utilized. Ability to access the extrinsic lateral ankle ligament (anterior talofibular), the extrinsic subtalar ligaments (calcaneofibular, lateral talocalcaneal) and the intrinsic subtalar ligaments (interosseous talocalcaneal, cervical) was evaluated. The first cadaveric specimen was dissected as a baseline to identify the extrinsic and intrinsic subtalar ligaments. The three remaining cadaveric specimens were utilized to evaluate the efficacy of three standard surgical approaches (a curvilinear incision made over the distal anterior border of lateral malleolus, a posterolateral longitudinal incision, and an extensile sinus tarsi approach) to access both the extrinsic ankle and subtalar ligaments as well as the intrinsic subtalar ligaments. Ability to access all ligaments as well as identification of neurovascular structures at risk during the dissection was recorded for each approach.Results:The curvilinear incision made over the distal anterior border of the lateral malleolus provided access to the anterior talofibular, calcaneofibular ligaments. Branches of the superficial peroneal nerve were noted to be at direct risk. The posterior longitudinal incision provided access to the calcaneofibular, lateral talocalcaneal ligaments. Branches of the sural nerve were noted to be at direct risk with this approach. An extensile posterolateral incision improved access to the anterior talofibular ligament. An extensile sinus tarsi approach provided the most direct access to the interosseous talocalcaneal and cervical ligaments. Visualization of the calcaneofibular and lateral talocalcaneal was also provided with this incision. The saphenous and superficial nerve branches and the sinus tarsi artery were noted to be at risk.Conclusion:We hypothesize that the intrinsic subtalar ligaments have a multiplanar role in ankle joint stabilization similar to that of the anterior cruciate ligament at the knee. Accurate identification and optimal surgical approach to these structures has not been well described in the orthopaedic foot and ankle literature. This cadaveric study provides evidence that an extensile sinus tarsi approach can provide access to the extrinsic ankle and subtalar ligaments as well as the intrinsic ligaments of the subtalar joint.

Detailed Anatomy of the Lateral Rectus Muscle-Superior Rectus Muscle Band.

Background To elucidate the detailed anatomy of the lateral rectus muscle-superior rectus muscle (LR-SR) band by cadaver eye investigation. Methods In total, 48 eyes of 24 cadavers were observed macroscopically. The lateral rectus muscle (LRM) and superior rectus muscle (SRM) were dissected from their origins to their insertions under the dissecting microscope, and the location, width, length, and tensile strength of the LR-SR bands were measured. Results The LR-SR band is the thick ligament interconnecting LRM pulleys with SRM pulleys. The LR-SR band was covered by the orbital part of the lacrimal gland superiorly, and the intermuscular septum between the LRM and SRM was shown anterior to the LR-SR band. The length of the attachment site between the LR-SR band and the SRM was less at 8.64 ± 1.52 mm (p=0.040), its thickness was thinner at 0.74 ± 0.16 mm (p=0.002), and its tensile strength was weaker at 7.64 ± 1.82 N (p=0.028) compared to the attachment site between the LR-SR band and the LRM. Conclusions This study revealed the detailed anatomy of the LR-SR band and provided helpful information to understand heavy eye syndrome and sagging eye syndrome.

Revision of Late Permian Nonmarine Bivalves of the Genus Opokiella Plotnikov, 1949

The genus Opokiella occurs in the Upper Permian (upper part of the Guadalupian–Lopingian) of the East European Platform, sharply differing from members of the Palaeomutela Fauna, which prevails in this territory throughout the Permian Period. Distinctive characters of Opokiella, such as the hinge with a tubercular cardinal tooth and individual pseudotaxodont teeth anterior and posterior to the umbo, thick opisthodent parivincular ligament, and mostly homogeneous shell microstructure, suggest that this group of nonmarine bivalves should be assigned to the monogeneric family Opokiellidae Kanev, 1983 (of the suborder Anthracosiidina Silantiev and Carter, 2011, order Cardiida Ferussac, 1822). The genus Opokiella is similar in external characters to nonmarine bivalves known from the Lopingian beds of Tanzania under the conventional name “Carbonicola.”

MR Arthrogram Features That Can Be Used to Distinguish Between True Inferior Glenohumeral Ligament Complex Tears and Iatrogenic Extravasation.

The purpose of this study is to identify features seen at shoulder MR arthrography that distinguish between iatrogenic contrast material extravasation and inferior glenohumeral ligament (IGHL) complex tears. MR arthrograms (n = 1740) were screened for extravasation through the IGHL complex. Cases were defined on the basis of surgical findings or definitive lack of extravasation in a fully distended joint immediately after contrast agent injection. The location of the disruption and the morphologic features of the torn margin were assessed and compared between groups. Anterior band disruption was present in eight of 16 patients with true tears and in zero of 19 patients with iatrogenic contrast material extravasation (p < 0.001). Isolated extravasation through the posterior half of the axillary pouch was present in 12 patients with iatrogenic extravasation, compared with none of the patients with true tears (p < 0.001). Thick ends were present in 10 of the true tears, whereas none of the cases of iatrogenic extravasation showed this finding (p < 0.001). Scarred margins were seen in eight true tears and none of the iatrogenic extravasation cases (p < 0.001). The presence of a torn anterior band, thick ligament, reverse-tapered caliber, and scarred appearance of the torn margin were shown to be 100.0% specific, and a torn posterior band showed 84.2% specificity for true tears. The presence of isolated involvement of the posterior portion of axillary pouch showed 63.2% sensitivity and 100.0% specificity for iatrogenic extravasation. A torn anterior band, a thickened ligament (> 3 mm), reverse-tapered caliber, and scarred margin were 100.0% specific for a tear. Isolated disruption of the posterior axillary pouch was 100.0% specific for iatrogenic extravasation.

Ligamental compartments and their relation to the passing spinal nerves are detectable with MRI inside the lumbar neural foramina

Intraforaminal ligaments (IFL) in lumbar neural foramina (NF) and their relation to the lumbar spinal nerves (SN) are addressed. Giemsa- and PAS-stained plastinated body slices of 15 lumbar spines were made and compared to MRI and CT data acquired of the same fresh specimens. We dissected one fixed lumbar spine to discuss our results with previous literature. Macroscopic pathophysiological changes and operational interventions at these lumbar spines were excluded. In the NF, thin medial IFL touch the SN. As a second compartment, intermedial vertical IFL are seen. A third lateral horizontal compartment of IFL is formed by thick cranial and caudal ligaments. Ligaments of the second and third compartments have no direct contact with the SN. From medial to lateral, the IFL thicken. All compartments are 3D reconstructed. If compartments of the IFL have no direct contact with the SN seen in the slices, a connection was noticed after dissection. Manual dissection seems to be inappropriate for a detailed study of the IFL. The lateral and intermedial compartments being free of the SN may transmit power and protect the SN, while the thin medial IFL may lead the SN passing the NF under physiological conditions. We conclude from the close topographical relation that the IFL may be relevant in foraminal stenosis. Any herniation in the NF presses IFL to the SN. Therefore, we think the IFL themselves could cause neurogenic claudication in case of their non-physiological turnover. Visualisation of IFL seems to be possible by using MRI. These slides can be retrieved under Electronic Supplementary Material.

Pediatric ACL Injuries: A Review of Current Concepts.

Background: The number of anterior cruciate ligament (ACL) injuries reported in skeletally immature athletes has increased over the past 2 decades. The reasons for this increased rate include the growing number of children and adolescents participating in competitive sports vigorous sports training at an earlier age and greater rate of diagnosis because of increased awareness and greater use of advanced medical imaging. There is a growing need for a consensus and evidence based approach for management of these injuries to frame a dedicated age specific treatment strategy.Methods: This article does a systematic evidence based literature review of management of Pediatric ACL injuries seen in several forms: tibial eminence avulsion fractures partial ACL tears and full thickness ligament tears and its outcome analysis.Results: The mechanism of Safe and effective surgical techniques for children and adolescents with ACL injuries continues to evolve. The numerous age matched techniques are extensively discussed. Neuromuscular training can reduce the risk of ACL injury in adolescent girls.Conclusion: This review outlines the current state of knowledge on diagnosis treatment and prevention of ACL injuries in children and adolescents and helps in guiding the treatment through a dedicated algorithm.

Effect of ao/W Ratio on Fracture Toughness Parameter of Extra Deep Drawn Steel Sheets: Experimental and Finite Element Studies

Fracture toughness parameter is significantly affected by specimen dimensions i.e. specimen thickness (B), width (W) and unbroken ligament length (W-ao) in elastic-plastic region. Present study is about the third dimension of test specimen (W-ao). In order to investigate effect of ao/W ratio on fracture toughness parameter, fracture test and finite-element - cohesive zone model (CZM) simulation tool are used. Fracture tests are carried out on extra deep drawn (EDD) steel sheets using compact tension (CT) type specimens with different ao/W ratio (0.5, 0.525, 0.55 and 0.575). After successive experimental attempts, load drop technique is used as a fracture criterion. Critical CTOD is used as a fracture toughness parameter. An alternative constant traction separation law is used to account for maximum load and large load line displacements. Experimental findings as well as finite element studies show that the critical CTOD decreases with ao/W ratio. It has been observed that as ao/W ratio increases, the location of plastic hinge shifts towards the crack tip (i.e. size of tensile plastic zone reduces), which reduces fracture toughness. That is, the material is less resistant to crack growth for deeper cracks.

Early spray development at high gas density: hole, ligament and bridge formations

Three-dimensional temporal instabilities, leading to spray formation of a round liquid jet segment with an outer, coaxial high-density gas flow, are studied with Navier–Stokes and level-set computations. These computations predict the liquid surface shape showing the smaller structures on the conical wave crests, i.e. lobes, holes, bridges and ligaments, which are the precursors to droplet and spray formations. These structures and their time scales affect droplet size and velocity distributions as well as spray cone angles. The gas-to-liquid density ratio, liquid Reynolds number ($Re$) and liquid Weber number ($We$) range between 0.02–0.9, 320–16 000 and 2000–230 000, respectively, which cover three distinct physical domains. (1) At higher $Re$ and $We$, ligaments and then drops develop following hole and liquid bridge formations. (2) At higher gas densities throughout the $Re$ range, several holes merge forming two bridges per lobe before breaking to form ligaments; this hole merging is explained by slower development of hairpin vortices and lobe shape. (3) In cases where both gas density and $Re$ or $We$ are lower, the well-ordered lobes are replaced by more irregular, smaller-scale corrugations along the conical wave crest edge; ligaments form differently by stretching from the lobes before holes form. Thicker ligaments and larger droplets form in the low $Re$, low gas density range. The surface wave dynamics, vortex dynamics and their interactions are explained. Understandings of liquid stream break up and concurrent smaller structure formation are built upon an examination of both translation and rotation of the fluid. In all cases, hole formation is correlated with hairpin and helical vortices; fluid motion through a perforation in the thin sheet near the wave crest corresponds to these vortices. The hole formation process is dominated by inertial forces rather than capillary action, which differs from mechanisms suggested previously for other configurations. Circulation due to streamwise vorticity increases while the lobes thin and holes form. For larger surface tension, cavities in the jet core rather than perforations in a sheet occur. The more rapid radial extension of the two-phase mixture with increasing gas density is explained by greater circulation in the ring (i.e. wave crest) region. Experimental descriptions of the smaller structures are available only at lower $Re$ and lower density, agreeing with the computations. Computed scales of bridges, ligaments, early droplets and emerging spray radii agree qualitatively with experimental evidence through the high $Re$ and $We$ domains.