Linear Fracture Research Articles

Fractal fracture toughness measurements of heat-treated granite using hydraulic fracturing under different injection flow rates

In geothermal energy extraction research, fractal fracture toughness measurements of high-temperature rocks during hydraulic fracturing have yet to be investigated but are crucial for hot dry rock reservoir reconstruction. In this paper, real-time high-temperature hydraulic fracturing tests at different injection flow rates were performed using thick-walled hollow cubic granite specimens with pre-crack. By introducing fractal theory, the fractal dimension was deployed to describe the tortuous morphology of the hydraulic fracture surface before establishing a fracture toughness theoretical model under fractal fracture. Acoustic emission events were monitored during fracturing, the effect of temperature and rate on the microstructure of the hydraulic fracture surface was examined using scanning electron microscopy (SEM) after fracturing. Finally, the effect of temperature and rate on hydraulic fracture characteristics and the correlation between fractal and fracture toughness were discussed. Experimental results showed that the fractal fracture toughness decreased with increasing specimen temperature and decreasing injection flow rate. As with other fracture characteristics such as breakdown pressure, fractal dimension, and microstructure, it was not governed by either temperature or rate alone, but was facilitated by the coupling of both factors, which could be explained by the thermal shock of high-temperature rock exposed to fracturing fluids. The results of fractal fracture toughness were greater than linear fracture toughness, which is attributed to greater fracture energy consumption due to mineral grains separation and micro-crack development associated with fractal fracture compared to linear fracture. This also indicated that fractal fracture toughness conformed favourably to the essence of rock fracture. These results can provide novel insights on the fracture mechanism of hydraulically fractured thermal reservoir at different injection flow rates.

Assessment of failure probabilities and the allowable size of defects in structural elements using the criteria of fracture mechanics

The possibility of assessing the safe size of the defects of metal continuity using risk criteria are considered. Such defects occur at all stages of the life cycle of structures. Assessment of their hazard and determination of their allowable size becomes important when the defects can lead to brittle or quasi-brittle fracture. In this case, models of linear and nonlinear fracture mechanics are used. In these models, defects are considered as internal elliptical or surface semi-elliptical cracks. The stochastic variety of shapes, sizes, locations, and orientations of defects has a significant effect on the destruction mechanisms. In this regard, the relevant probabilistic problem of assessing the permissible size of defects according to the criteria of the risk of destruction comes to the fore. We consider a general approach to assessing hazard of defects by risk criteria. Two settings of the probabilistic problem of risk assessment based on of one- and two-parameter fracture criteria are presented. The risk function in the form of the probability of fracture according to a given criterion is used as the main calculated characteristic. The expression of the risk function based on one-parameter criteria of fracture mechanics is presented. The main attention is paid to the probabilistic model based on the two-parameter fracture criterion by E. M. Morozov. This criterion provides ample opportunities for analyzing fracture mechanisms with a change in the size of defects. An expression for the risk function based on the family of two-dimensional probability distributions of Lu – Bhattacharya of the Weibull type is obtained. It is shown that the correlations of the fracture mechanisms can significantly affect the values of the fracture probabilities, and, consequently, the allowable size of defects.

Three-dimensional dynamic fracture analysis using scaled boundary finite element method: A time-domain method

A time-domain method for modeling three-dimensional transient dynamic fracture problems is developed based on the scaled boundary finite element method (SBFEM). For this purpose, a cracked polyhedron modeled by the SBFEM is constructed to simulate the through-thickness crack in the domain. The mass and stiffness matrices of polyhedrons are derived and assembled to form the three-dimensional elastodynamic equations in the time domain. High-order elements are used to improve computational accuracy. The dynamic response is evaluated by the Newmark method, and the stress field is expressed semi-analytically. Based on the theory of linear ealstodynamic fracture mechanics, the static stress intensity factors are extended to the dynamic stress intensity factors (DSIFs) by considering the dynamic effect. The DSIFs are directly extracted from the analytical solution in the radial direction of the cracked polyhedron. Numerical examples are modeled to validate the presented method. Good agreement is observed between the computed results and the published results in the literature. The effects of the time step, mesh density, and material damping coefficient on the computational accuracy are also investigated. It is found that moderately sized third-order elements can lead to very good solutions, and an increase of both the orders or number of elements does not significantly improve the accuracy of the simulation. The distribution of the DSIFs along the crack front of the 3D models is investigated and it is found that the DSIFs vary strongly along the crack front.

Active crack control approach applied to a horizontal rotating machine

The present contribution proposes an active vibration control technique devoted to shafts with cracks aiming to minimize their propagation. The existence of a crack in rotating shafts can be characterized by 2X and 3X super-harmonic amplitudes in the vibration responses of the rotor, which can increase as the crack propagates along the shaft’s cross-section. A proportional-integral-derivative control technique is applied to suppress the 2X and 3X vibration amplitudes of a cracked shaft, which is performed by using a bandpass filter applied to the vibration responses of the rotor. Numerical and experimental results are obtained through both a representative finite element model of a horizontal rotor and its corresponding test-rig. In this case, electromagnetic actuators are used to apply the control effort to the rotor. The Mayes model is applied for simulating the breathing behavior of the transverse crack. The linear fracture mechanics theory is considered to correlate the crack depth with the corresponding additional rotor flexibility. Both numerical and experimental results demonstrate the possibility of reducing the effects of a transverse crack through active control on the dynamic behavior of a rotating machine. Moreover, it is shown that the proposed control law is capable of controlling the crack effects with the rotor operating in different rotation speeds.

Fast penetration of Ga in Al: liquid metal embrittlement near the threshold of grain boundary wetting

Abstract The thermodynamic conditions for spontaneous grain boundary wetting and stress driven liquid metal embrittlement are related to each other and the kinetic mechanism responsible for fast GB penetration under small stress is described. The dissolution – condensation mechanism of liquid metal embrittlement and linear fracture mechanics for calculation of a crack profile are applied to the classical system “Al – liquid Ga”. The results tend to support the idea that the recently observed fast linear penetration of Ga along 150° tilt <110> GB of Al should be considered as propagation of a liquid metal embrittlement crack under a small residual stress rather than as spontaneous grain boundary wetting. With the residual tensile stress σ ≈ 0.5 MPa acting normal to the GB plane, all major findings reported for this model system are explained in a semiquantitative way assuming that the GB spreading coefficient is extremely small by its absolute value, i. e. that the system is near the threshold of spontaneous grain boundary wetting.

The Link Between Skull Fracture and Extradural Hematoma in Head Injury Patients who came to a Tertiary Care Hospital in Pakistan

Aim: The purpose of our current study is to see if there is any connection between skull fracture and extradural hematoma in head injury patients who came to the tertiary care hospital in Pakistan. Methods: From January 2020 to December 2021, this descriptive research was conducted at Chandka Medical College, Shaheed Mohtrama Benazir Bhutto Medical University Larkana. The research comprised those patients who have undergone extradural hematoma surgery during study period. Normal skull X-rays being taken, and the type and position of fractures were documented on the X-rays, CT scan, and during surgery. The frequency of skull fracture linked through extradural hematoma was studied in different ages. SPSS version 24.0 was utilized to investigate our current findings. Results: A sum of 130 individuals were operated on for extradural hematoma. In 70 cases, a linear fracture was seen, and in 18 individuals, a depressed skull fracture was seen. Another ten individuals with no radiologically evident fracture reported discovered to also have a fracture line intra-operatively. As a result, 87 (78 percent) of the participants suffered a skull fracture. Here remained no statistically important variation in occurrence of skull fracture among age ranges. Conclusion: Although there is a significant link between skull fracture and extradural hematoma, a normal X-ray does not rule out extradural hematoma. Keywords: Skull fracture, extradural hematoma, head injury, Tertiary Care Hospital, Larkana, Pakistan.

Influence of nanoparticulate diameter on fracture toughness enhancement of polymer nanocomposites by an interfacial debonding mechanism: A multiscale study

Herein, we propose a multiscale modeling framework to predict the fracture toughness enhancement of polymer nanocomposites due to interfacial debonding and subsequent plastic nanovoid growth mechanisms. As far as we know, this is the first attempt to develop a multiscale modeling framework by merging all-atomistic molecular dynamics (MD) simulations, micromechanics, and the linear fracture mechanics theory. The elastoplastic constitutive law of interphase and interfacial energy were characterized using a multiscale bridging modeling approach based on the all-atomistic MD simulations and mean-field (MF) homogenization. Our results showed that the nanoparticulate radius influenced the elastoplastic constitutive law of interphase and interfacial energy. Based on the proposed framework, we investigated the influence of the nanoparticulate radius on the fracture toughness enhancement. We expect the results of this study to reveal the influence of the interphase on the fracture toughness enhancement of polymer nanocomposites and provide useful guidelines for the rational selection of toughening agents.

Pattern and distribution of injuries in fatal motorized two-wheeler accident cases - A prospective study

In India, motorized two-wheelers are an extremely popular form of transport, and they are more commonly involved in road traffic accidents (RTAs) than other vehicles. Occupants of motorized two-wheelers are more prone to sustaining serious injuries, which are responsible for greater morbidity and mortality among them. This study was conducted to assess the pattern and distribution of injuries and the causes of death in fatal RTAs involving motorized two-wheelers. This is a prospective study of 100 cases of RTAs involving riders and pillion riders of motorized two-wheelers, which were brought for autopsy in the mortuaries of J.J.M. Medical College and Chigateri General Hospital, Davangere over 2 years. In our study, the head and neck regions were found to be most commonly involved, and abrasions were the most common external injury. Intracranial hemorrhages were found to be the most common head injury. The most commonly involved skull bone was the base of the skull, and linear (fissured) fracture was the most common type of skull fracture. The commonest intracranial hemorrhage was subarachnoid hemorrhage. Frontal lobes suffered maximum injury, and contusions were the most common brain tissue injury. The most common thoracic injuries were rib fractures. The liver was the most commonly injured solid organ. More injuries were seen in the thoracic and lumbar regions of the vertebrae. The humerus was the most common upper limb bone to be fractured. The femur was the most common lower limb bone to be fractured. Head and neck injuries were responsible for deaths in the majority of the victims.

Prediction of fracture strength for products with single or multiple holes

Conventional linear notch mechanics, proposed in the 1980s, clarifies the distinction between the fracture zone and non-fracture zone of notched materials and is useful for evaluating the fracture strength of brittle materials. While linear fracture mechanics, a method for evaluating the strength of cracked materials, requires only one measure of severity, the stress intensity factor K, this conventional linear notch mechanics requires two measures. The two measures are the maximum stress at the bottom of the notch and the notch radius. In this study, we clarify the effectiveness of an improved linear notch mechanics that uses the stress gradient at the bottom of the notch instead of the notch radius, and refer to the extension of applicability.

Asymmetric Bilateral Traumatic Epidural Hematoma: A Report of a Rare Traumatic Lesion

Bilateral epidural hematoma is a rare presentation in head trauma injuries, accounting for only 1%-2% of all epidural hematomas, but with a higher mortality rate than the unilateral form. Herein, we report the case of a 27-year-old man admitted to our department following a road traffic accident. On admission,his Glasgow Coma Scale (GCS) score was 13/15. After a few minutes, he became comatose (GCS 6/15) with right anisocoria. CT scan revealed a bilateral asymmetric epidural hematoma with a left extralabyrinthic linear fracture. Surgical evacuation was subsequently performed, starting with the voluminous right hematoma. The patient was discharged on the 23rd postoperative day with a right third-nerve palsy. Conclusions: In this case report, we discuss the etiology, mechanism, and management of bilateral epidural hematoma. Early diagnosis and a judicious surgical approach for bilateral epidural hematoma are necessary to minimize mortality and morbidity. Prevention is key to reducing traumatic brain injuries.

Effect of the Stress State on the Adhesive Strength of an Epoxy-Bonded Assembly

The paper studies the adhesive strength of aluminum alloy specimens bonded with the use of an epoxy adhesive, under the tensile-shear stress state, depending on the testing temperature. Tension of modified Arcan specimens with load angles of 0, 22.5, 45, 67.5, and 90° with respect to the plane of adhesion is chosen as the experimental method. Experiments were performed at temperatures of −50, +23, and +50 °С. The analysis of the obtained results yields a linear fracture criterion and a fracture locus for the adhesive failure strain energy density, which takes into account the ratio of the elastic properties of the adhesive to those of the substrate. The region bounded by the fracture loci of adhesive strength and ultimate strain energy density determines the conditions for the safe loading of the bonded assembly in terms of the energy and force criteria of adhesive failure. The proposed fracture loci can be used, preferably simultaneously, to estimate the in-service strength and reliability of adhesively bonded assemblies.

SIS therapy in the treatment of distal radius epiphyseal fracture (Case report)

Introduction. Fractures of the distal radius epiphysis are the most common fractures of the upper limb, present both in the general population active following major trauma and in the elderly population in minimal trauma due to osteoporosis. Among the adjuvant therapies for orthopedic treatment of distal radius epiphyseal fracture we can list Super Inductive System (SIS), a therapy based on the interaction between the electric field and the human body with the improvement of the healing process by acting on the pathophysiological stages of bone callus. Material and method. A clinical case study was performed on a 28-year-old patient, hospitalized and treated in the neurosurgery department of the Constanta County and Emergency Hospital for a polytrauma by road accident (passenger) with amyelotic cervical vertebral trauma, thoracic trauma and trauma to the right upper limb, subsequently performing 12 SIS therapy sessions at the Balneal and Rehabilitation Sanatorium of Techirghiol. CT examination of the cervical spine reveals fractures of C4 vertebra (the blade and pedicle) and C5 vertebra (vertebral body, lamina and pedicle). Right forearm radiography reveals fracture of the right radial styloid. After conservative treatment of the cervical injury and orthopedic treatment of the upper limb injury, the clinical evolution is favorable, allowing the patient to be discharged and allowed to do 12 sessions of SIS therapy, 3 times a week, within 4 weeks. The subsequent clinical and paraclinical evolution was favorable for the outpatient orthopedic ambulatory reevaluation performed at 5 weeks. Results and discussions. Due to the type of fracture of the radial distal epiphysis (linear fracture without displacement), absence of comorbidities and young age, led to the indication of orthopedic treatment with immobilization in the antebrachio-palmarcast, which allowed subsequent physiotherapy. Keywords: radial fracture, callus, polytrauma, cervical spine, lamina, Super Inductive System,

FATIGUE ASSESSMENT OF CORRODED DECK LONGITUDINALS OF TANKERS


 
 
 Fatigue life of deck longitudinals of oil tankers is analysed based on linear elastic fracture mechanics. A parametric formulation for the estimation of stress intensity factors and the Paris-Erdogan law are applied. Long-term effects of corrosion are modelled based on regression equations fitted to thickness measurements made during inspections of two tankers. Parametric studies are performed in order to investigate the importance of the governing parameters of crack propagation. A comparison of the fatigue analyses performed by linear fracture mechanics and S-N approaches is presented.
 
 

Traumatic Head Injury and the Diagnosis of Abuse: A Cluster Analysis.

Data guiding abusive head trauma (AHT) diagnosis rest on case-control studies that have been criticized for circularity. We wished to sort children with neurologic injury using mathematical algorithms, without reference to physicians' diagnoses or predetermined diagnostic criteria, and to compare the results to existing AHT data, physicians' diagnoses, and a proposed triad of findings. Unsupervised cluster analysis of an existing data set regarding 500 young patients with acute head injury hospitalized for intensive care. Three cluster algorithms were used to sort (partition) patients into subpopulations (clusters) on the basis of 32 reliable (κ > 0.6) clinical and radiologic variables. P values and odds ratios (ORs) identified variables most predictive of partitioning. The full cohort partitioned into 2 clusters. Variables substantially (P < .001 and OR > 10 in all 3 cluster algorithms) more prevalent in cluster 1 were imaging indications of brain hypoxemia, ischemia, and/or swelling; acute encephalopathy, particularly when lasting >24 hours; respiratory compromise; subdural hemorrhage or fluid collection; and ophthalmologist-confirmed retinoschisis. Variables substantially (P < .001 and OR < 0.10 in any cluster algorithm) more prevalent in cluster 2 were linear parietal skull fracture and epidural hematoma. Postpartitioning analysis revealed that cluster 1 had a high prevalence of physician-diagnosed abuse. Three cluster algorithms partitioned the population into 2 clusters without reference to predetermined diagnostic criteria or clinical opinion about the nature of AHT. Clinical difference between clusters replicated differences previously described in comparisons of AHT with non-AHT. Algorithmic partition was predictive of physician diagnosis and of the triad of findings heavily discussed in AHT literature.

Traumatic brain injury of childhood

Traumatic brain injury of childhood

Characteristics and clinical findings of traumatic brain injury patients in single referral hospital dr. Hasan Sadikin hospital, Bandung, West Java, Indonesia

Introduction: Traumatic brain injury (TBI) is the leading cause of mortality and morbidity in children and young adults globally. Knowledge of TBI characteristics holds importance on the treatment improvement of and scientific progression. Thus, this study aimed to evaluate the characteristics of TBI in Hasan Sadikin Hospital.Methods: Analysis of data obtained from a retrospective review of medical records and from a systematic database pertaining to diagnostic criteria of TBI treated in the Department of Neurosurgery at Dr. Hasan Sadikin Hospital, Bandung, Indonesia from January 1st 2012 to December 31st 2018.Results: This study included 10,234 cases over the described time period. Men had a higher prevalence of TBI (7,539 patients or 73.7%) compared to women (2,695 patients or 26.7%). The majority of the cases were mild TBI (68.3%). The most common skull fracture was linear fracture (68.6%), while the majority of skull base fracture was anterior skull base fracture (66.7%). The majority of intracranial lesions were cerebral contusion (26.4%). Intracranial lesions were commonly observed in patients with moderate or severe than mild TBI.Conclusion: The incidence of accompanying intracranial lesions and skull fracture were commonly observed in patients with moderate or severe TBI than patients with mild TBI.Keywords: alcohol intoxication, intracranial lesions, skull base fracture, skull fracture, traumatic brain injury

Neglected Growing Skull Fracture: Details on Peroperative Findings and Surgical Repair

Growing Skull Fracture (GSK) is a rare but significant complication of pediatric head trauma. It commonly develops after a head trauma with a linear skull fracture and an underlying dural tear. Delayed diagnosis and improper management can lead to severe complications. Few reports provide details on peropeartive findings and surgical management of GSF. Herein we report the case of a neglected growing skull fracture in a 2-year-old infant who suffered from an abuse head trauma at the age of three months. A progressive bulging at the site of the fracture was neglected by the family for months. CT scan of the brain showed gliotic brain tissue herniated through a large ragged skull defect. Surgery was indicated and the goals of operation were to remove safely nonviable herniated brain tissue and to protect the neural elements by restoring dural and bone defect. Surgery should be performed acutely in children with GSF to reduce the morbidity and improve outcome.

EVALUATION OF STRENGTH PARAMETERS OF POLYMER COMPOSITES USED FOR DENTAL RESTORATION BY THE METHOD OF ACOUSTIC EMISSION

The aim of the study is to create a technique and perform mechanical tests to determine the strength parameters of dental composites from the standpoint of linear fracture mechanics, and using the phenomenon of acoustic emission to determine the origin and development of destruction of light-curing dental composites under quasi-static local compression load. The following hybrid dental composites of domestic and foreign manufacturers were selected for comparison: Latelux (Latus, Ukraine), TETRIC N-CERAM (Ivoclar Vivadent, Liechtenstein), CHARISMA CLASSIC (Kulzer, Germany). 10 disc samples of 13 mm diameter and 5 mm thick of each material were made by using a specially designed mould for study purposes. Packaging and moulding of the material into the mould was performed in laboratory conditions at an air temperature of 18 – 21°C. Before testing, the samples were kept for 24 hours at a temperature of 37°C in saline solution. The samples were loaded on the SVR-5 machine using a ball indenter. During the experiments, acoustic emission data were simultaneously recorded using the SKOP-8 measuring system. In the post-processing stage, the dependencies of the load change during the experiment, the distribution of the amplitudes of the registered AE signals and their sum over time were recorded. The fracture load, indenter displacement, and the features of composite fracture were determined from the obtained dependencies based on the analysis of AE generation under the load. Analysis of the parameters of the AE signals showed that during the destruction of the Tetric N-Ceram composite the signals had the largest amplitude and energy, and of Latelux had the smallest ones.

Determination of Mechanical and Fracture Properties of Silicon Single Crystal from Indentation Experiments and Finite Element Modelling.

It is well-known that cracks are observed around the impression during indentation of brittle materials. The cracks inception depends on load conditions, material and indenter geometry. The paper aims to use experimental micro-indentation data, FE simulations with cohesive zone modelling, and an optimisation procedure to determine the cohesive energy density of silicon single crystals. While previous studies available in the literature, which use cohesive zone finite element techniques for simulation of indentation cracks in brittle solids, tried to improve methods for the evaluation of material toughness from the indentation load, crack size, hardness, elastic constants, and indenter geometry, this study focuses on the evaluation of the cohesive energy density 2Γ from which the material toughness can be easily determined using the well-known Griffith-Irwin formula. There is no need to control the premise of the linear fracture mechanics that the cohesive zone is much shorter than the crack length. Hence, the developed approach is suitable also for short cracks for which the linear fracture mechanics premise is violated.

The effect of fracture growth rate on fracture process zone development in quasi-brittle rock

The nonlinear development zone in front of the rock fracture tip, called fracture process zone (FPZ), could affect the propagation of fracture. Understanding the effect of fracture growth rate on FPZ could provide guidance for engineering applications such as hydraulic fracturing. In this paper, a pressure-driven fracture device was adopted to carry out Model-Ⅰ fracture test on sandstone specimens. Based on the cohesive zone model, a criterion was proposed to identify the tip of traction-free fracture and the boundary of FPZ using Digital Image Correlation (DIC) method. The fracture growth rates were calculated during the fracture process, where the FPZ length and shape were characterized. It was found that the fracture growth rate could affect the FPZ length significantly. In the linear fracture growth stage, FPZ is nearly constant in length, semi-elliptical in shape; in the exponential fracture propagation stage, FPZ lengthens with fracture growth rate, and its shape grows from a semi-ellipse to a band. A cohesive zone model considering fracture growth rate was established to describe the softening function, fracture energy, and the characteristic length of FPZ, from which the effect of fracture growth rate on characteristic length was analyzed, indicating that the FPZ length increases at a high fracture propagation rate because of the decrease of brittleness in rock.