Rupture Criterion Research Articles

Finite element analysis of macro-crack behavior in the cortical bone of a human tibia

The bone is a biological tissue that possesses a highly complicated hierarchical structure; hence, the tissue components of the bone exhibit variable mechanical proper-ties and a complex bone geometry. This is why the creation of a three-dimensional mod-el through CAD software facilitates the study of the mechanical behavior of bones. Com-bining the concepts of linear elastic fracture mechanics and finite element analysis pro-vides a practical solution to study the fracture behavior of the tibial bone. The objective of this study is to analyze the behavior of cracks in the cortical bone of the human tibia us-ing stress intensity factors in mode I, II, and III as rupture criteria to assess the bone damage response. The tibial bone is one of the most common sites for lower limb stress fractures, which pose problematic injuries. The results investigating the effect of the crack position in the bone demonstrate that the risk of crack propagation is mainly due to mode I opening and is highly favored in the distal zone compared to the middle and proximal regions, regardless of bone density. For the second case study, it is observed that regardless of the crack size, the maximum values of stress intensity factors KI are obtained in the distal zone. Regarding the effect of crack orientation, the results indicate the dominance of mode II for angles α = – 45°, 30°, 45°, leading to high values of stress intensity factors KII.

Equivalent conversion of different multiaxial stress rupture criteria for creep materials based on skeletal point stresses

Multiaxial creep life prediction of components has been challenging. To cope with the challenge, efforts have been made to develop suitable multiaxial stress rupture criteria (MSRC) based on representative stress concept. Of all MSRCs, the ones due to Sdobyrev and Hayhurst-Leckie (denoted as SHL MSRC), and to Cane (denoted as Cane MSRC) are commonly-used. In this work, the equivalent conversion between the SHL MSRC and the Cane MSRC is investigated based on skeletal point stresses. Equivalent conversion formulae are proposed based on the skeletal point stresses of circumferentially-notched tension (CNT) specimen, and then validated by comparison with the experimental data available in the literature. The equivalent conversion formula between the two MSRCs is found to be dependent on the signs of principal stresses. Therefore, different conversion formulae should be chosen depending on the signs of principal stresses. Afterwards, the applicability of different equivalent conversion formulae is demonstrated for the CNT specimen when skeletal point stresses are available, and for creep crack growth specimen when skeletal point stresses are not available. Finally, the equivalence of the two MSRCs is discussed.

In vivo mechanical characterization of arterial wall using an inverse analysis procedure: application on an animal model of intracranial aneurysm.

Intracranial aneurysm is a pathology related to the deterioration of the arterial wall. This work is an essential part of a large-scale project aimed at providing clinicians with a non-invasive patient-specific decision support tool to facilitate the rupture risk assessment. It will lean on the link between the aneurysm shape clinically observed and a database derived from the in vivo mechanical characterization of aneurysms. To supply this database, a deformation device prototype of the arterial wall was developed. Its use coupled with medical imaging (spectral photon-counting computed tomography providing a spatial resolution down to 250 μm) is used to determine the in vivo mechanical properties of the wall based on the inverse analysis of the quantification of the wall deformation observed experimentally. This study presents the in vivo application of this original procedure to an animal model of aneurysm. The mechanical properties of the aneurysm wall identified were consistent with the literature, and the errors between the numerical and experimental results were less than 10%. Based on these parameters, this study allows the assessment of the aneurysm stress state for a known solicitation and points towards the definition of a rupture criterion.

Determination of multiaxial creep stress rupture criteria for 316H stainless steel at 600 °C

In this work, the applicability of three different methods, denoted as the direct method, the indirect method, and the simple empirical method based on uniaxial creep damage tolerance parameter, λ, for the determination of multiaxial stress rupture criterion (MSRC) is assessed. The assessment involves four commonly-used MSRCs, the Sdobyrev and Hayhurst-Leckie (denoted as SHL), the Cane, the Nix and the Huddleston MSRCs. To this end, creep tests on both uniaxial and circumferentially-notched tension (CNT) specimens of 316H stainless steel are carried out at three net-section stress levels, that is, 300 MPa, 320 MPa and 340 MPa, and at 600 °C. The results show that all the three methods are suitable for the determination of MSRC for the steel examined. Of these, the direct method data-based simple empirical equation is attractive as it takes good advantage of uniaxial creep data in terms of reflecting the operative creep failure mechanism, and therefore may serve as an alternative for the determination of the SHL MSRC, particularly when multiaxial test data is not available. Moreover, the determined SHL, Cane and Huddleston MSRCs are found to be equally effective in the creep life prediction of both uniaxial and CNT specimens, while the effectiveness of the Nix MSRC in life prediction depends on position for stress output and material. In addition, factors influencing the determination of MSRC for stainless steels are discussed in terms of experimental data available in the literature.

The role of asymmetry and volume of thrombotic masses in the formation of local deformation of the aneurysmal-altered vascular wall: An in vivo study and mathematical modeling.

Currently, the primary factor indicating the necessity of an operation for an abdominal aortic aneurysm (AAA) is the diameter at its widest part. However, in practice, a large number of aneurysm ruptures occur before reaching a critical size. This means that the mechanics of aneurysm growth and remodeling have not been fully elucidated. This study presents a novel method for assessing the elastic properties of an aneurysm using an ultrasound technique based on tracking the oscillations of the vascular wall as well as the inner border of the thrombus. Twenty nine patients with AAA and eighteen healthy volunteers were considered. The study presents the stratification of a group of patients according to the elastic properties of the aneurysm, depending on the relative volume of intraluminal thrombus masses. Additionally, the neural network analysis of CT angiography images of these patients shows direct (r = 0.664271) correlation with thrombus volume according to ultrasound data, the reliability of the Spearman correlation is p = 0.000215. The use of finite element numerical analysis made it possible to reveal the mechanism of the negative impact on the AAA integrity of an asymmetrically located intraluminal thrombus. The aneurysm itself is considered as a complex structure consisting of a wall, intraluminal thrombus masses, and areas of calcification. When the thrombus occupies > 70% of the lumen of the aneurysm, the deformations of the outer and inner surfaces of the thrombus have different rates, leading to tensile stresses in the thrombus. This poses a risk of its detachment and subsequent thromboembolism or the rupture of the aneurysm wall. This study is the first to provide a mechanistic explanation for the effects of an asymmetrical intraluminal thrombus in an abdominal aortic aneurysm. The obtained results will help develop more accurate risk criteria for AAA rupture using non-invasive conventional diagnostic methods.

A physics-based failure study of smart artificial tissues in human-like soft robots

Artificial tissues made of fiber-reinforced elastomers typically have mechanical properties similar to biological tissues. Such a similarity motivates artificial tissue usage in building human-like soft robots aiming primarily to perform a wide range of human-like motions and effectively interact with the human environment. Soft robots can be ripped or damaged for unknown reasons in a variety of applications. The literature has no unified stress-based criterion for predicting the critical zones of artificial tissues undergoing deformations. Such a unified stress-based criterion typically entails detecting internal damage and establishing the stress limit criterion based on the maximum stretching threshold. The current study establishes an experimentally validated rupture criterion for a novel class of smart artificial tissues made of electro-active polymers motivated by biological tissue damages in several robust conditions. A thermodynamically consistent mechanoelectrical deformation model is formulated, demonstrating that such tissues have inherent anisotropy that must be taken into account when modeling such materials. Later, a continuum physics-based rupture model is derived as a unified stress-based criterion to investigate the effect of physical parameters associated with artificial tissue failure. A well-known octahedral stress-based von Mises failure theory is adopted to examine all the principal deformation modes of artificial tissues up to rupture.

Time-dependent plastic behavior of bacteria leading to rupture

A study of the mechanical response of bacteria is essential in designing an antibacterial surface for implants and food packaging applications. This research evaluated the mechanical response of Escherichia coli under different loading conditions. Indentation and prolonged creep tests were performed to understand their viscoelastic-plastic response. The results indicate that varying loading rates from 1 μm/s to 5 μm/s show an increase in modulus of 182% and 90%, calculated in the loading and unloading cycles, respectively, and a decrease in adhesion force by 42%. However, on varying loads from 5 nN to 25 nN, nominal change is observed in both modulus and adhesion force. The rupture curve at 100 nN load shows elastic and a small plastic deformation accompanied by a sharp peak indicating the cell wall rupture. The rupture force at the peak was found to be 34.38 ± 5.15 nN, irrespective of the loading rate, making it a failure criterion for bacteria rupture. The creep response of bacteria increases (for 6 s) and then remains constant (for 15 s) with time, indicating that a standard linear solid (SLS) model applies to this behavior. This work attempts to evaluate the mechanical properties of E. coli bacteria focusing on its rupture by contact killing mechanism.

Effect of hydraulic fracturing induced stress field on weak surface activation during unconventional reservoir development

Unconventional reservoirs usually contain many weak surfaces such as faults, laminae and natural fractures, and effective activation and utilization of these weak surfaces in reservoirs can significantly improve the extraction effect. In hydraulic fracturing, when the artificial fracture approaches the natural fracture, the natural fracture would be influenced by both the original in-situ stress field and the hydraulic fracturing-induced stress field. In this paper, the hydraulic fracturing-induced stress field is calculated based on the relative position of hydraulic fracture and natural fracture, the original in-situ stress, the net pressure inside the hydraulic fracture and the pore pressure of the formation. Furthermore, the stability model of the natural fracture is established by combining the Mohr-Coulomb rupture criterion, and extensive parametric studies are conducted to explore the impact of each parameter on the stability of the natural fracture. The validity of the proposed model is verified by comparing with the reservoir characteristics and fracturing process of the X-well 150–155 formation in the Songliao Basin. It is found that the stress field induced by the hydraulic fracture inhibits the activation of the natural fracture after the artificial fracture crossed the natural fracture. Therefore, for similar reservoirs as X-well 150–155, it is suggested to connect natural fractures with hydraulic fractures first and then activate natural fractures which can effectively utilize the natural fractures and form a complex fracture network.

Micromechanics and damage in slide-ring networks.

We explore the mechanics and damage of slide-ring gels by developing a discrete model for the mechanics of chain-ring polymer systems that accounts for both crosslink motion and internal chain sliding. The proposed framework utilizes an extendable Langevin chain model to describe the constitutive behavior of polymer chains undergoing large deformation and includes a rupture criterion to innately capture damage. Similarly, crosslinked rings are described as large molecules that also store enthalpic energy during deformation and thus have their own rupture criterion. Using this formalism, we show that the realized mode of damage in a slide-ring unit is a function of the loading rate, distribution of segments, and inclusion ratio (number of rings per chain). After analyzing an ensemble of representative units under different loading conditions, we find that failure is driven by damage to crosslinked rings at slow loading rates, but polymer chain scission at fast loading rates. Our results indicate that increasing the strength of the crosslinked rings may improve the toughness of the material.

Dynamic monitoring of morphological and hemodynamic evolution of small cerebral aneurysms

Highlights. Small cerebral aneurysms (<3 mm), which make up the majority of aneurysms, rupture more frequently, although medium (>3 mm) and giant (>15 mm) aneurysms and have a higher risk of rupture. This article proves for the first time that the rupture risk criteria developed for giant cerebral aneurysms do not work for small aneurysms. The development of small aneurysms in patients was analyzed and measured morphological features of aneurysms were compared with their calculated hydrodynamic characteristics.Aim. To study the dynamics of development of small cerebral aneurysms, to assess the applicability of existing methods for calculating the risk of rupture, to formulate new clarifying hypotheses for calculating the risk of rupture of small cerebral aneurysms.Methods. Patient data were provided by the Federal Center for Neurosurgery, Novosibirsk. CT angiography was performed using a Philips Ingenuite CT scanner (Philips Medical Systems, USA, 128 slices). Aneurysm size dynamics was assessed by measuring three main sizes with an accuracy of 0.1 mm using the IntelliSpace Portal Philips software environment. Numerical calculations were carried out using ANSYS CFX 2020R2.Results. Hemodynamic characteristics change according to the changes of the aneurysm dome. In the case when morphological characteristics of the aneurysm have not changed, a change in the geometry of the patient's circle of Willis (coW) is observed: the curvature of the arteries, the angles of bifurcations (the structure of coW remained unchanged). The PHASES score (absolute risks of rupture for aneurysms) was found to be unusable for the considered aneurysms.Conclusion. This work formulates and morphologically and hydrodynamically confirms for the first time in the volunteers that the change in risk estimates for such aneurysms is fundamentally affected, even insignificantly, by the change in the circle of Willis: a change in the curvature of individual segments of the cerebral arteries, as well as the angles of their bifurcations. The results obtained are aimed at modifying the existing risk criteria for rupture of cerebral aneurysms.

Evaluating the Degree of Tectonic Fracture Development in the Fourth Member of the Leikoupo Formation in Pengzhou, Western Sichuan, China

The extent of fracture development is associated with the degree of enrichment of a natural gas reservoir and its productivity. Based on numerical simulation results of the paleotectonic stress field, a set of evaluation methods for determining the degree of development of reservoir tectonic fractures were established using rock rupture criteria. Taking the fourth member of the Leikoupo Formation in the Pengzhou area of western Sichuan as an example, a finite element (FE) method was employed to simulate the paleo-tectonic stress field during the period of fracture development, and the degree of tectonic fracture development was further evaluated using the above methods. The results indicated that effective fractures were created in the Himalayan period. In this time, mainly NE–NEE and nearly E–W strike tectonic fractures were developed in the target layer. The fractures were mainly low-angle and oblique fractures, while the high-angle fractures were less developed. According to the integrative fracture index (F), five typical fracture development areas were determined: the fault zone, and the northern, eastern, southeastern, and central regions of the study area. The reliability of the fracture prediction results was verified using fracture distribution statistics and gas production test results.

Determination of multiaxial stress rupture criteria for creeping materials: A critical analysis of different approaches

• Factors affecting different methods for the determination of MSRC are analyzed. • Principles in the determination of MSRC are recommended. • The factor, α , is strongly dependent on the operative creep failure mechanism. • A relation exists between multiaxial factor, α , and damage tolerance parameter, λ . Materials in engineering applications are rarely uniaxially-loaded. In reality, failures under multiaxial loading has been widely observed in engineering structures. The life prediction of a component under multiaxial stresses has long been a challenging issue, particularly for high temperature applications. To distinguish the mode of failure ranging from a maximum principal stress intergranular damage to von Mises effective stress rupture mode a multiaxial stress rupture criterion (MSRC) was originally proposed by Sdobyrev and then Hayhurst and Leckie (SHL MSRC). A multiaxial-factor, α , was developed as a result which was intended to be a material constant and differentiates the bias of the MSRC between maximum principal stress and effective stress. The success of the SHL MSRC relies on accurately calibrating the value of α to quantify the multiaxial response of the material/geometry combination. To find a more suitable approach for determining MSRC, the applicability of different methods are evaluated. Given that the resulting analysis of the various approaches can be affected by the creep failure mechanism, principles in the determination of MSRC with and without using continuum damage mechanics approaches are recommended. The viability of uniaxial material parameters in correlating with α through the analysis of available data in literature is also presented. It is found that the increase of the uniaxial creep damage tolerance parameter λ is accompanied by the decrease of the α –value, which implies that the creep ductility plays an important role in affecting the multiaxial rupture behavior of materials.

Experimental investigation and numerical prediction of rupture in SS304 stainless steel sheet under tension

This work is focused on prediction of rupture in the tensile tests of SS304 stainless steel sheet. The tensile test experiments were performed up to rupture and the strain was measured using extensometer and digital image correlation (DIC) system. The experimental results obtained from the tensile tests were utilized for the numerical simulation. In the numerical simulation, four macroscopic rupture criteria were used to predict rupture. The numerical results show the good agreement with the experimental results. Damage factor was calculated using the macroscopic rupture criteria in numerical simulation. The critical values of the damage factor based on the macroscopic criteria were obtained at rupture in simulation. These values are unique for all the mechanical tests and can be utilized for prediction of rupture in numerical simulation of mechanical tests. This study shows that Oh, Brozzo and Ayada criteria have good agreement for strain at rupture whereas Rice-Tracey criterion doesn’t show any agreement within the range of triaxiality from 0 to 0.66.

Uncovering the hydride orientation-mediated hoop fatigue mechanism in a zirconium alloy cladding tube

Hydride reorientation degrades the mechanical performance of Zr alloys. However, the mechanism by which hydride reorientation affects fatigue behavior is unclear. In this study, the effect of hydride orientation on crack initiation, propagation, and failure during hoop fatigue loading of a Zr–Sn–Nb alloy cladding tube was systematically investigated. The results show that the presence of ∼20% radial hydrides, in addition to circumferential hydrides, reduces fatigue life by 33%. Hydride-related cracking initially appears in intergranular or transgranular hydrides regardless of the orientation of the hydride. In circumferential hydrides, cracking initially appeared through the rupture of hydrides along their thickness, followed by crack growth either along the hydride–matrix interface or inside the hydrides. By contrast, for radial hydrides, cracks initially appeared at the hydride–matrix interface and always propagated along the interface. Radial hydrides provide favorable paths for fatigue crack growth, which contributes to the lower fatigue life of the hydride-reoriented samples. Subsequently, the rupture criterion of hydrides is discussed. A method for the quantitative calculation of grain-boundary stress was proposed, which allowed for the establishment of an accurate relationship between the critical size of the hydride and the critical strain of the matrix. Finally, a possible rationale for the crack deflection of circumferential hydrides is provided.

On strain-based rupture criterion for ascending aortic aneurysm: The role of fiber waviness

We propose a new approach for constructing strain-based rupture criterion for ascending thoracic aortic aneurysm. The rupture metric is formulated using an effective strain, which is a measure of net strain that the collagen bundles experience after fiber uncrimping. The effective strain is a function of the total strain and the waviness properties of the collagen fibers. In the present work, the waviness properties are obtained from fitting biaxial response data to constitutive models that explicitly consider the collagen waviness and fiber recruitment. Inflation test data from 10 ascending thoracic aortic aneurysm specimens are analyzed. For each specimen, tension-strain data at ∼2300 material points are garnered. The effective strain fields in the configuration immediately before rupture are computed. It is found that the hotspots of the effective strain match the rupture sites very well in all 10 samples. More importantly, the values of effective strain at the hotsopts are closely clustered around 0.1, in contrast to a much wider distribution of the total strain. The study underscores the importance of considering the fiber recruitment in formulating strain-based rupture metric, and suggests that ϵ¯≈0.1, where ϵ¯ is the effective strain metric defined in this work, can be considered as a criterion for assessing the imminent rupture risk of ascending aortic aneurysms. Statement of significanceWe advocate to use effective strain in ATAA rupture assessment. The effective strain is a measure of net strain in the collagen network after waviness uncrimping. We analyzed bulge inflation data of ATAA samples. It was found that, while the total strains at rupture varied from sample to sample, the effective strains were closely clustered around 0.1. And the hotspots of effective strain matched the rupture sites well. The work underlines the importance of considering collagen fiber waviness and recruitment when evaluating the rupture risk using strain, and suggests a new direction for developing sharper rupture metrics.

VAPING-INDUCED ALVEOLAR RUPTURE LEADING TO PNEUMOMEDIASTINUM IN A YOUNG FEMALE

TOPIC: Disorders of the Mediastinum TYPE: Medical Student/Resident Case Reports INTRODUCTION: Electronic cigarette use or "vaping" has been on the rise in America over the last decade. Literature shows that approximately 8.1 million Americans admitted to vaping in 2018. Vaping is when one inhales and exhales an aerosolized solution (Vaper) through a cigarette-like electrical device. Some chemicals found in vapers have been linked to disease processes. While using E-cigarettes, the participant inhales a large amount of vaper, exaggerating the Valsalva maneuver, subsequently increasing intra-thoracic pressure. This increase in thoracic pressure places the participant at risk for spontaneous pneumomediastinum. We present a case of a 19-year-old female diagnosed with spontaneous pneumomediastinum. The only risk factor, the use of electric cigarettes. CASE PRESENTATION: A 19-year-old female with a history of type 1 diabetes mellitus and vape dependence presents with a 3-day history of abdominal pain, chest pain, and retching. She admitted to vaping daily for one year before the presentation. Physical examination revealed no evidence of respiratory distress along with slight crepitus tracheal area at the level above the clavicle. She was found to be in diabetic ketoacidosis (DKA), which was also treated. She continued to have epigastric burning along with chest pain. For this reason, computed tomography (CT) of the chest was performed and showed pneumomediastinum. She did not meet the Pittsburg criteria for esophageal rupture. Barium swallow eventually ruled out esophageal rupture. The pneumomediastinum likely occurred secondary to vape-induced alveolar rupture. She was treated with supplemental oxygen, and serial chest radiograph showed gradual resolution of pneumomediastinum. DISCUSSION: Laennec first described pneumomediastinum (PM) in 1819 as a consequence of traumatic injury. The clinical presentation could be very vague, ranging from classic chest pain to unspecific symptoms, which lead to delayed diagnosis. The pathophysiology of can be described by the Macklin effect as follows: (a) alveolar rupture, (b) air dissection along the bronchovascular sheath, and (c) free air reaching the mediastinum. Chest radiography, the standard diagnostic procedure, diagnosis can be confirmed by chest computed tomography scan. Once the diagnosis is approved, the patient should be admitted for monitoring and treatment consisting of avoidance of the trigger factors, oxygen, and bed rest. CONCLUSIONS: Spontaneous pneumomediastinum secondary to vaping is on the rise. The diagnosis of vaping-induced lung injury continues to be a dilemma among physicians. A high index of suspicion is necessary for early detection and treatment. Although most cases are benign, it will be prudent for health care providers to actively query patients about their use and educate patients on their potential severe side effects. REFERENCE #1: Pneumomediastinum: Practice Essentials, Pathophysiology, Epidemiology. Accessed April 28, 2021. https://emedicine.medscape.com/article/1003409-overview REFERENCE #2: Marasco RD, Loizzi D, Ard NP, Fatone FN, Sollitto F. Spontaneous Pneumomediastinum After Electronic Cigarette Use. Ann Thorac Surg. 2018;105:e269-e271. doi:10.1016/j.athoracsur.2017.12.037 REFERENCE #3: Panacek EA, Singer AJ, Sherman BW, Prescott A, Rutherford WF. Spontaneous pneumomediastinum: Clinical and natural history. Ann Emerg Med. 1992;21(10):1222-1227. doi:10.1016/S0196-0644(05)81750-0 DISCLOSURES: No relevant relationships by Esiemoghie Akhigbe, source=Web Response No relevant relationships by Ebubechukwu Ezeh, source=Web Response No relevant relationships by Mackenzie Hamilton, source=Web Response No relevant relationships by Mohamed Suliman, source=Web Response

Evaluation of inclined crack in mixed mode I and II

In this work,we tented to study the mixed mode of failure with two angles of inclination, of a treated steel, for that we tried to determine the parameters of failure as the stress intensity factor, tenacity and the critical energy in mixed mode of a rupture and see the criterion of rupture and seeing the effect of the angles evolution applied for all parameters. of in our close there is a fragile and less ductile rupture.

A stress-weighted ductile fracture model for steel subjected to Ultra Low Cycle Fatigue

A new criterion is proposed to simulate the initiation of ductile fracture due to Ultra-Low Cycle Fatigue (ULCF). Building on previous research, the new fracture criterion broadens the scope of ULCF models to account for a broader range of multi-axial stress and strain states that may be encountered in steel structures. The model formulation, supported by observations from finite element plasticity simulations of void growth and fractographic analyses of fracture surfaces, describes damage accumulation as a function of plastic strain, stress triaxiality, and the Lode stress parameter. The damage rate model is integrated over arbitrary cyclic loading histories of local strains and stresses to predict ULCF fracture. The proposed criterion (termed the Stress Weighted Ductile Fracture Model – SWDFM) is supported by a series of 66 coupon scale experiments on two grades of low-carbon structural steel (A572 and A36). These tests interrogate a range of positive and negative stress triaxiality with absolute values between 0.1 and 1.6, Lode stress parameters between 0 and 1, and monotonic and cyclic loading histories. The SWDFM criterion, which requires the calibration of only two material parameters for the materials investigated in this study, is evaluated against the experimental test data using an average-error assessment as well as a cross-validation analysis. Three other ULCF rupture criteria are similarly assessed and compared. The SWDFM is shown to accurately predict ULCF initiation over a wide range of stress states and loading histories, suggesting that the model represents well the micro-mechanical mechanisms of ULCF.

Determination of barometric criteria for rupture of atherosclerotic plaques in the brachiocephalic arteries

The sequence of determining determination of the critical value of blood pressure for the occurrence of dissection of atherosclerotic intima of the internal carotid artery according to the experimental study. Atherosclerotic lesion of the brachiocephalic arteries was modeled on a vascular silicone phantom of the carotid arteries, in which the surgical material (intact annular area of atherosclerotic intima with plaque), obtained after eversion endarterectomy in a patient with atherosclerotic lesions, was placed and fixed in the region of the mouth of the internal carotid artery. A total of 30 models were created. To determine the critical values of the pressure on the intima with the plaque, at which it ruptures, balloon catheters were used, controlling the pressure with a manometer. The results were compared with the preoperative data of ultrasound and computed tomography examinations of patients. Dissection of the intima in the area of the plaque occurred in 6 cases at a pressure of 150180 mm Hg; in 9 cases at 180200 mm Hg, in 3 cases at a pressure of more than 200 mmHg, in 12 when exposed to more than 300 mm Hg. All patients, whose intima ruptured at a pressure of less than 200 mm Hg, had a fluid component of the plaque on preoperative examination, and in 6 patients, the critical pressure on the plaque was 150 mm Hg., there was also a thinned "cover" of the plaque. In the rest of the cases, the plaques were stable without a liquid component. Dissection of the intima in these cases did not occur when the exposure value was more than 300 mm Hg. The presence of a fluid component in an atherosclerotic plaque of the carotid artery in combination with a thinned cover of the plaque indicates the extreme danger of its destruction and embolism during a hypertensive crisis. The degree of stenosis of the carotid artery was found to be a less significant risk factor for unstable plaque rupture than the presence of a fluid component.

A predictive modeling tool for damage analysis and design of hydrogen storage composite pressure vessels

In this paper, a predictive modeling tool is developed for damage analysis and design of hydrogen (H2) storage composite pressure vessels. It integrates micromechanics of matrix cracking into a continuum damage mechanics (CDM) description for damage evolution, and three-dimensional (3D) finite element (FE) modeling of the vessel structural response. At the scale of the composite layer (mesoscale), the temperature-dependent stiffness reduction law in terms of the damage variable for transverse matrix cracking is computed using an Eshelby-Mori-Tanaka approach (EMTA) for the initial composite thermoelastic properties and a self-consistent model for the stiffness reduction as a function of the damage variable. While transverse matrix cracking obeying a damage evolution relation can progressively evolve from an initiation to a saturation state, fiber failure is predicted by a micromechanical fiber rupture criterion that accounts for the fiber strength and matrix stress that can be computed within EMTA. The implementation of this integrated multiscale modeling model into a 3D FE formulation enables damage analysis and design of H2 storage composite pressure vessels. The developed tool is illustrated through 3D damage analyses of a cryogenically compressed H2 storage vessel model subjected to thermomechanical loadings to investigate effects of the helical layer fiber orientation and loading scenario on damage development, vessel integrity and burst pressure.