Crack Lips Research Articles

Phase Field Fracture Model for Assessing the Load Bearing Capacity of Fractured Glass

The use of glass as structural material has highlighted the need for more reliable numerical approaches to analyze its mechanical behavior, especially in the accidental eventuality of fracture. Modelling the behavior of fractured laminated glass, in fact, is fundamental to assess the Post-Fracture load-bearing capacity. However, this is a highly challenging task because of the many interplaying factors, such as the viscoelastic and thermal-dependent behavior of the interlayer, the presence of a highly complex and variable crack pattern and the interaction among fragments. The objective of the present work is the development and testing of a robust numerical model that can naturally introduce the generated crack pattern into virtual specimens and manage the interaction among many fragments. The phase field fracture model is herein explored, by assigning the damage variable to fit the pre-existing crack pattern. Then, the specimen is loaded letting the phase field managing the fragments interaction. The dependence of the stress tensor with the damage variable is herein defined through the Cleavage-Deviatoric model, since it prevents fully damaged regions from transmitting tensile and shear stresses yet keeping their ability to bear compressive forces. Indeed, this model can asymptotically reproduce unilateral and frictionless contact conditions between the existing crack lips. Preliminary case studies are discussed to check the potentiality of the proposed approach.

A strain gage technique for measuring the mode II stress intensity factors

In this paper, we propose a strain gage technique that allows an accurate measurement of the mode II stress intensity factors (SIFs). In order to ensure a good KII measurement, the size of the correct radial location of the strain gages is identified by using a methodology based on finite element analysis (FEA) and consolidated by solid theoretical foundations. The extent r1,max and r2,max of the validity of the five- and six-term representation of generalized Westergaard stress functions, which requires the use of two and three strain gages, respectively, is determined using the proposed method, and its dependence on the crack length to width ratio is also investigated. Numerical results obtained are in good agreement with the theoretical predictions, and confirm that the present method makes it possible to determine the KII with high precision when two (or three) strain gages are well placed within r1,max (or r2,max). Also, the numerical experiments show that the use of three strain gages is necessary when the size of the linear behavior region r1,max is very small. In addition, the effect of friction between the crack lips was checked and shown to have no effect on KII in pure mode II.

A reverse identification of the friction coefficient operating within crack lips through a complete elastoplastic simulation of 3D fretting fatigue cracks

This study investigates the fretting fatigue cracking process for wires made of aluminum alloy through elastic and elastoplastic simulations of former tests where both crack arrest and crack growth until failure were observed. A three-dimensional finite element analysis (FEA), incorporating 3D cracks within the contact, is conducted to replicate the experiments in the conditions of these former results. The present study demonstrates that an elastic assumption fails to capture the threshold crack extension, which would result in systematically underestimated lengths for crack arrest. When considering elastoplastic behavior of the aluminum strands, instead of elastic behavior, the SIF values evolve consistently with experimental observations. By this way, it is now possible to carry out a sounded FEA so as to account for friction in the crack lips in the presence of plasticity. First, this model clarifies the role of friction in crack arrest. Secondly, a reverse analysis is proposed to assess the associated coefficient of friction between crack lips, yielding a value consistent with measurements obtained from gross slip fretting experiments.

Revisiting classical concepts of Linear Elastic Fracture Mechanics - Part I: The closing ‘mathematical’ crack in an infinite plate and the respective Stress Intensity Factors

This is the first part of a short three-paper series, aiming to revisit some classical concepts of Linear Elastic Fracture Mechanics. The motive of this first paper is to highlight some controversial issues, related to the un­natu­ral overlapping of the lips of a ‘mathematical’ crack in an in­fin­­­ite plate load­ed by specific combinations of principal stresses at in­finity (predicted by the clas­si­c­al solu­tion of the respective first fundamental problem), and the closely as­so­ciated issue of negative mode-I Stress Intensity Factor. The problem is con­­­front­ed by superimposing to the first funda­mental problem of Lin­ear Elastic Frac­ture Mechanics for an in­fin­ite cracked plate (with stress-free crack lips) an ‘in­­verse’ mixed fund­amental problem. This superposition provides naturally ac­­­­­­­­ceptable stress and displacement fields, prohibiting overlapping of the lips (by means of contact stresses generated along the crack lips, which force the over­lapped lips back to naturally accepted position) and, also, non-negative mode-I Stress Intensity Factors. The solu­tions of this first paper form the basis for the next two papers of the series, dealing with the respective prob­lems in fi­­n­ite do­­mains (recall, for example, the cracked Brazil­ian disc con­fig­u­ra­tion) weak­­ened by artificial notches (rather than ‘math­e­mat­ical’ cracks), by far more interesting for practical engineer­ing ap­pli­­ca­tions.

A simple, robust novel Williams series-based FE-analytical hybrid technique for evaluation of SIFs and higher order coefficients

To evaluate crack-tip parameters, various hybrid methods (HMs) amalgamating experimental domain data with multi-parameter field-variable expressions have been extensively employed. On the other hand, simpler HMs leveraging boundary contour data and demonstrating the robustness of the HMs for input data errors have been scarcely reported. In this regard, the present work addresses these gaps by proposing and illustrating a novel HM coupling coarse-mesh FE boundary displacement data on the crack lips, but not limited to it, with Williams’s series. Additionally, the HM’s robustness for simulated Gaussian error distribution in the input data is demonstrated. Comparison of HM-computed SIF values with converged FE values shows rapid convergence after 2–3 terms in the series and a certain number of retrieving points. Histogram analyses quantifying the deviations of HM-computed SIFs in the sample set indicate error tolerance within a reasonable limit for the fracture modes. These observations demonstrate the efficacy of the HM; In addition, the HM yields higher-order coefficients — accuracy of which are corroborated by comparing reconstructed field variables in the vicinity of the crack-tip with converged FEA. On the other hand, robustness analyses demonstrate that ±1σ of the data is within about 10% of error for all the modes. Thus, the proposed simple and robust HM offers a potential practical approach for evaluation of SIFs and higher order coefficients.

A case of Multisystem Inflammatory Syndrome in Children (MIS-C)

Multisystem inflammatory syndrome in children (MIS-C) is a systemic disorder involving persistent fever, extreme inflammation and organ dysfunction, which is temporally associated with exposure to COVID-19. onset may be delayed or contemporary with ongoing SARS-CoV-2 infection. Here we present a case of 4-year-old girl, who was presented with high grade fever, bilateral non-purulent conjunctivitis, generalized macular rash, dry and cracked lips with strawberry tongue, abdominal pain and diarrhoea, having contact with patient of COVID-19. She had neutrophilic leukocytosis with thrombocytosis and very high inflammatory markers, CXR demonstrated bilateral peripheral patchy opacities, RT-PCR for COVID-19 was negative. According to diagnostic criteria this patient was diagnosed as Multisystem inflammatory syndrome in children (MIS-C) which is temporally associated with COVID-19 and treated successfully.
 AKMMC J 2021; 12(1) : 62-65

Numerical analysis of frictional contact between crack lips in the framework of Linear Elastic Fracture Mechanics by a mesh-free approach

In this paper, a mesh-free approach is presented for the numerical analysis of frictional contact in the framework of Linear Elastic Fracture Mechanics (LEFM). This approach (WLS-HOCM) is obtained by combining a Weighted Least Square approximation (WLS) under a strong formulation with a High Order Continuation Method (HOCM), the Coulomb friction model and the visibility criterion to investigate the contact that occurs between the crack lips under compression loads. The contact between the crack lips is regarded as boundary conditions, and a regularization technique is used to replace these no-smoothed conditions with smoothed ones. We were able to avoid the numerical integration encountered in the weak formulation by using the strong formulation. The stick and slip phenomena of closed cracks are studied using numerical examples. The numerical results obtained demonstrate the effectiveness and precision of the suggested method for computing frictional self contact problems.

68 The confounder in time of confusion: a case report on Multisystem Inflammatory Syndrome in Children (MIS-C)

68 The confounder in time of confusion: a case report on Multisystem Inflammatory Syndrome in Children (MIS-C)

Behavior in mixed-mode of desiccation cracks on a clayey rock front gallery

This study reports on the mixed-mode behavior of desiccation cracks in a clayey rock front gallery. As most digital image correlation (DIC) algorithms have access to the full-field measurements of the displacements and strains, the improvements in DIC now allow the automatic detection of the jumps in the displacements induced by the opening and sliding of desiccation cracks without imposed initial conditions. This new local data allows us to specifically study the kinematics of the crack lips at each deformed state. These results allow us to quantify the opening and sliding of cracks and the cracked area during the desaturation and saturation paths of the rock mass. Amongst other results, a linear trend between the deformation of the solid phase and the crack porosity is observed. The results also demonstrate that most desiccation cracks evolve in a mixed-mode, the values of the shear component are of the same order of magnitude as the opening values.

Nontypical presentation of a common disease: a case report

BackgroundKawasaki disease is an idiopathic medium-sized vasculitis that occurs primarily in infants and children younger than 5 years of age. Atypical Kawasaki disease applies to patients who do not fulfill the complete criteria of fever of 5 days or more with at least four of five features: bilateral conjunctival injection, changes in the lips and oral cavity, cervical lymphadenopathy, extremity changes, and polymorphous rash. Acute kidney injury is defined as a sudden decline in kidney function within hours, including structural injuries and loss of function. Acute kidney injury is extremely common in hospitalized pediatric patients. However, it is rarely documented in Kawasaki disease. Acute kidney injury is underestimated in Kawasaki disease due to the lack of a clear definition of age-specific normal serum creatinine levels and routine renal functions. This report describes a case who presented with clinical features suggestive of atypical Kawasaki disease and developed acute kidney injury.Case presentationA 2-year-old Saudi girl had a history of high-grade fever for 5 days, moderate dehydration, dry cracked lips, poor appetite, and generalized erythematous rash; therefore, she was diagnosed to have incomplete Kawasaki disease. Laboratory investigations revealed normochromic normocytic anemia, leukocytosis, thrombocytosis, high inflammatory markers, and acute kidney injury stage III. An echocardiogram showed a 4-mm dilatation on the left main coronary artery and a 3-mm dilatation on the right. A renal biopsy was not performed to identify the cause of the injury as it showed improvements after the start of the specific therapy for Kawasaki disease; intravenous immune globulin at a dose of 2 g/kg, aspirin at a high dosage of 80 mg/kg/day, and prednisolone at 2 mg/kg. In addition to the acute kidney injury management, normal saline boluses were followed by furosemide at a 2 mg/kg dose. Her urine output increased, and her renal functions normalized. She was discharged in good condition after 10 days.ConclusionsIt is valuable to check renal function tests in a confirmed case of Kawasaki disease to reduce the negative consequences of late acute kidney injury discovery. Early detection and intervention make a substantial difference in acute kidney injury management.

The time administration and cost burden of intravenous immunoglobulin (IVIG) therapy in a 4-year-old girl with Kawasaki disease: A case report

Kawasaki disease (KD) is an acute systemic vasculitis frequently affecting children under five years old. KD can cause severe complications. It can lead to coronary aneurysms in 15-25% of untreated cases. Intravenous immunoglobulin (IVIG) treatment within ten days of initial onset can reduce the rate of coronary artery aneurysms. However, IVIG administration in Indonesia is currently limited due to its high cost. The case reported a 4-year-old girl with a chief complaint of fever. She complained about a high fever seven days before hospitalization. She also complained about vomiting, cough, joint pain, diarrhea, skin peeling, and rash on her body, palms, and soles. On examination, she looked irritable and sluggish. The temperature was 39.9o C. There were red eyes without discharge, strawberry tongue, oral thrush, and red, dry, cracked lips, swollen neck lymph nodes, and skin rash on her body, palms, and soles. Laboratory testing showed microcytic hypochromic anemia with Hb 7.9 g/dL and leukocytosis 24.230/mm3. Chest X-ray showed perihilar and paracardial infiltrates. Electrocardiogram revealed sinus tachycardia. An echocardiogram showed left ventricle dilatation with trivial mitral regurgitation and no coronary abnormalities were found. She was diagnosed with Kawasaki Disease. She was treated by IVIG 30 gr single dose during 12 hours on day 7 of initial onset, methylprednisolone injection 10 mg/8 hours, paracetamol 150 mg/8 hours, and aspirin 400 mg/8 hours orally and discharged from the hospital with improvement. There weren’t any coronary artery abnormalities found. IVIG administration within ten days of initial onset in KD patients can reduce the risk of coronary artery complications. IVIG administration after day 10 of initial onset can achieve resolution of inflammation but can be insufficient for preventing coronary artery lesions (CALs).

The Prevalence of using Prescribed & Unprescribed “Roaccutane (Isotretinoin)” among Females Riyadh, Saudi Arabia: A Cross Sectional Study

Aims: To determine the prevalence of using prescribed and unprescribed Isotretinoin and to assess knowledge of its adverse effects among females in Riyadh, SA.
 Study design: cross-sectional study.
 Place and Duration of Study: online questionnaire collected throughout two months by distributing the questionnaire via. social media platforms.
 Methodology: We included 385 female patients (age range 15-45 years) use Roaccutane (Isotretinoin) with or without prescribed. Statistical analysis was performed using Rv 3.6.3. Counts and percentages was used to summarize the distribution of categorical variables and data. Chi-square test was used to estimate the association between categorical variables. Hypothesis testing was performed at a 5% level of significance.
 Results: 568 respondents completed the questionnaire. Of these, 440 were from Riyadh. The majority of respondents were aged 15 – 20 (46.4%) and 21 – 25 (35.2%). Knowledge regarding some side effects of Roaccutane was significantly higher in respondents who reported using Roaccutane than those who did not. Knowledge of dry and cracked lips as a side effect was significantly higher in users (91.9%) than non-users (73.1%). Similarly, knowledge regarding dry eyes, depression, continuous thirst, nose dryness, bleeds, and effect of Roaccutane on liver biochemical profile, lipid profile, and bones was higher in users than non-users, regarding the teratogenic effect of Roaccutane was insignificantly different between groups.
 Conclusion: Females in Riyadh are aware of the side effects of isotretinoin, particularly dryness of the skin, eyes, and lips. Yet there is insufficient knowledge regarding its teratogenic effect. Based on the reported results, a few participants obtained Roaccutane without a prescription from the doctor, and some obtained their information from unreliable sources (i.e., friends/relatives). Our results suggest good practice towards the prescription of isotretinoin.

The Association between Malnutrition and Oral Health in Older People: A Systematic Review

The aim of this systematic review was to examine the association between malnutrition and oral health in older people (≥ 60 years of age). A comprehensive systematic literature search was performed in four databases (PubMed, CINAHL, Dentistry and Oral Sciences Source, and Embase) for literature from January 2000 to May 2020. Both observational and intervention studies were screened for eligibility. Two reviewers independently screened the search results to identify potential eligible studies, and assessed the methodological quality of the full-text studies. A total of 3240 potential studies were identified. After judgement for relevance, 10 studies (cross-sectional (n = 9), prospective cohort (n = 1)) met the inclusion criteria. Three studies described malnourished participants as having fewer teeth, or functional (tooth) units (FTUs), compared to well-nourished participants. Four studies reported soft tissue problems in malnourished participants, including red tongue with blisters, and dry or cracked lips. Subjective oral health was the topic in six studies, with poorer oral health and negative self-perception of oral health in malnourished elderly participants. There are associations between (at risk of) malnutrition and oral health in older people, categorized in hard and soft tissue conditions of the mouth, and subjective oral health. Future research should be focused on longitudinal cohort studies with proper determination of malnutrition and oral health assessments, in order to evaluate the actual association between malnutrition and oral health in older people.

FE modeling of concrete with strong discontinuities for 3D shear fractures and comparison with experimental results

In this paper, a new Enhanced Finite Element Method (E-FEM) model is proposed to describe 3D shear fractures of quasi-brittle materials such as concrete. Special attention is made to the failure behaviors in cyclic loadings as it is a common phenomenon in practical engineering. Within the framework of the E-FEM, the discontinuities are locally embedded in the finite elements. Here, two kinds of discontinuity enhancements are used in this model: weak discontinuities allow the model to represent heterogeneities in an unstructured mesh explicitly, and strong discontinuities enable the displacement jumps in finite elements to perform cracks and fractures. In this paper, our interest is focused on the shear sliding discontinuity (mode-II). The closure mechanism is also taken into concern, which simulates frictional sliding forward and backward between the lips of cracks. Then the performance of the proposed model is tested and analyzed by comparing it to experimental results. Certain limitations of the simulation are pointed out, and the corresponding solutions are addressed. Finally, the consistencies and differences between the simulation and the experimental results are discussed.

Fracture processes imaging in concrete using nonlinear ultrasound

This paper shows the complementarity of two nonlinear ultrasonic imaging methods to characterize closed macro cracks in concrete. A time reversal mirror is used to locally probe and image the nonlinearity of a cracked region. Two nonlinear parameters are extracted to map the cracked region. The image obtained using the first parameter relates the harmonic generation due to the contact and frictional behaviors at the crack lips, correlated with vibro-thermography imaging of the same crack. The image obtained using the second parameter is based on the conditioning of the material induced by distributed micro cracks arising from the fracture process zone. These results show a great potential for characterization of fracture processes in concrete, with the possibility to uncouple the effects of the crack itself from surrounding distributed micro damage.

Stability Analysis of Carrot-based Natural Moisturising Lip Balm

Moisturising lip balm is an essential cosmetic product to enhance the lips appearance as well as to prevent inflammation or cracked lips. Lip balm with moisturising function formulated using all-natural ingredients is very significant because of the negative side effect awareness among people on using the unnatural or chemically derived ingredients of the lip balm. However, the stability analysis of this natural lip balm must be conducted to ensure the safety of the product as well as to predict the product shelf life. This study aims to evaluate the stability of carrot lip balm in two weeks under room temperature and refrigerator condition. Three lip balms with different concentration of virgin coconut oil (VCO) to carrot (35:65, 38:62, 43:57) were formulated and tested for their physicochemical properties (texture, colour, pH and spread ability) for two weeks. Lip balms with ratios of 35:65 and 38:62 were the best formulations as they presented good result in spread ability criteria in the stability test. From the observations, lip balms showed some changes at different temperature and time because of the degradation of natural ingredients. The product shelf life can be predicted from this stability test.

Crack path tracking using DIC and XFEM modelling of mixed-mode fracture in wood

A wedge split test in mode I and mixed-mode was designed and performed for wood at structural component scale. The displacement fields around cracks during propagation were recorded and analysed to provide information on crack tip position, the composition of deformation modes, resistance to fracture propagation, and separation of the crack lips. The data were fed into a non-linear numerical finite element model. A cohesive zone model based on the eXtended Finite Element Method was applied for mixed-mode fracture in 2D rectilinear orthotropic materials. Extrinsic exponential traction-separation laws for modelling mixed-mode splitting of wood from Norway spruce along the grain were calibrated to experimental crack data. The chosen model captures well the damage initiation and crack propagation in wood along the grain. The simulation results show the importance of initial crack length and actual mode composition as model parameters.

Multisystem Inflammatory Syndrome in Children Temporally Related to COVID-19: A Case Report From Saudi Arabia

The World Health Organization is still revising the epidemiology of multi-system inflammatory syndrome in children (MIS-C) and the preliminary case definition, although there is a dearth of robust evidence regarding the clinical presentations, severity, and outcomes. Researchers, epidemiologists, and clinicians are struggling to characterize and describe the disease phenomenon while taking care of the diseased persons at the forefronts. This report tackles the first case of a 13-year-old Saudi female with the MIS-C mimicking Kawasaki disease. Her main manifestations were fever, gastrointestinal symptoms, evidence of organ failure with an increase in inflammatory markers, and a history of coronavirus disease (COVID-19) infection. She had glucose-6-phosphate dehydrogenase (G6PD) deficiency and no significant previous history of any disease. She presented with signs of acute illness: high-grade fever (39.6°C) for five days accompanied by sore throat, malaise, reduced oral intake, abdominal pain, diarrhea, skin rash, bilateral non-suppurative conjunctivitis, and erythematous, cracked lips. Eventually, she died despite aggressive management based on the Centers for Disease Control and Prevention and the Saudi Ministry of Health guidelines for COVID-19 management. Based on this case, we suggest that pediatricians need to be aware of such atypical presentations and early referral to tertiary care is imperative for further early diagnosis and management.MIS-C is a rare yet severe and highly critical complication of COVID-19 infection in pediatrics, leading to serious and life-threatening illnesses. Knowledge about the wide spectrum of presenting signs and symptoms and disease severity, including early detection and treatment, is pivotal to prevent a tragic outcome.

Subpixel precision of crack lip movements by Heaviside‐based digital image correlation for a mixed‐mode fracture

AbstractThis study reports on the Heaviside‐based digital image correlation (H‐DIC) procedure and its application in fracture analysis. This improved DIC procedure was proposed to solve the uncertainty problems at the vicinity of the crack and to evaluate the opening and shear movements of crack lips and the orientations of cracks in the subset. Some tests were conducted to demonstrate the performance of the H‐DIC algorithm. An application on argillaceous rock mass exhibiting multiple mixed‐mode fractures is shown to validate the efficiency and robustness of the proposed method. This application consisted in processing images acquired from an experimental investigation performed in a gallery front submitted to climatic seasonal variations. The results illustrated how the H‐DIC procedure enables to localise and to quantify the opening, shearing and orientation of subpixel cracks. A sensibility study performed on the opening and shear components demonstrated that the precision of crack aperture by H‐DIC procedure is close to 0.14 pixel and the spatial resolution is equal to one pixel. Moreover, the crack area was calculated from local apertures on a monitoring duration of 1 year, and a maximum value of 595.8 mm2 in winter was obtained.

Closure of parallel cracks: Micromechanical estimates versus finite element computations

3D finite element simulations have been performed in order to assess the ability of five classical micromechanical estimates to model the elastic behavior of solids with parallel cracks, namely the dilute, Mori-Tanaka, self-consistent and differential schemes and the Ponte-Castaneda and Willis bounds. The cracks have been represented in the simulations by right circular cylinders with aspect ratios as low as 10−3 and with centroids randomly located in the REV. Special attention has been paid to the crack aspect ratio variation predicted by the different schemes, since the goal is ultimately to propose a non-linear micromechanical model of a cracked solid, taking complete crack closure into account.The results confirm earlier studies which showed that the differential scheme was best suited for this kind of morphology when computing elastic moduli, but additionally, we show that changes in crack aperture are also accurately predicted. It is however noted that the randomness in the positions of the cracks leads to significant scatter in the magnitude of the aperture variation inside a given simulation, which suggests that the cracks do not close simultaneously. As a consequence, non-linear numerical simulations accounting for contact between the crack lips should be performed in order to completely validate a non-linear micromechanical model in alternate tension/compression loading cases.