Dynamic caustics experimental study on interaction between propagating crack and deformity inclusions in primary structure

The approach combining the dynamic caustics method with high-speed photography technology is used to study the interaction between propagating cracks and three kinds of deformity inclusions（ cylinder inclusion, quadruple inclusion and triangular inclusion） under lowvelocity impact loading. By recording the caustic spots of crack tips at different moments during the crack propagation, the variation regulations of dynamic stress intensity factors（ DSIF） and crack growth velocity with respect to time are obtained. The experimental results showthat the resistance effects to crack growth are varied with different shapes of inclusions in specimens, and the quadruple inclusion＇s effect is more apparent. The distortion degree of caustic spots is affected by the shapes of inclusions as well, and the situation is more serious for cylinder and quadruple inclusions. The overall values of DSIFs of triangular inclusion specimen are greater than the others, and the crack growth velocities, characteristic sizes and DSIFs showprocesses of fluctuations because of the disturbance of reflection waves in specimens. The results provide an experimental basis for the analysis of strength and impact-resistance ability in structures with deformity inclusions.

Caustics study of the effect of glass fibres on dynamic fracture of hardened cement paste

The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.

Dynamic caustics test of blast load impact on neighboring different cross-section roadways

Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.

Dynamic fracture behavior of rock under impact load using the caustics method

We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.

A STUDY OF DYNAMIC CAUSTICS AROUND RUNNING INTERFACE CRACK TIP

Based on the first invariant of stress singular field in the vicinity of running tip of an interface crack, mapping equations of the caustic curve on the reference plane and the initial curve on the specimen plane are developed. The dynamic caustics are analyzed for the crack propagating along the interface between two bonded dissimilar materials. The variation of the caustic configurations is shown with the velocity change of the running crack and the ratio change of the stress intensity factors. Two characteristic dimensions are proposed that are not only practically measurable from optical caustic contours but also suitable to represent the behavior of transient caustics.

Study on dynamic fracture behavior of TA15ELI alloy under mode-Ⅱ loading by caustics method

The dynamic fracture behavior of TA 15ELI alloy with lath-like microstructure was studied by caustics method. Specimens with double-side pre-notch were tested under the plane-stress condition at mode-II loading with a drop hammer system. Caustics information recorded in films illustrated the histories of both crack length and stress intensity factor. The dynamic fracture toughness and crack growth velocity of TA15ELI with lath-like microstructure were determined to be 279 MPa.m1/2 and 32.6 m/s, respectively. SEM fractograph analysis showed a mixed feature of mainly plastic mode for TA 15ELI alloy in dynamic mode-II fracture. Shear localization was observed in the vicinity of the crack initiation area.

EXPERIMENTAL RESEARCH ON STRESS INTENSITY FACTOR K_Ⅲ FOR 3-D CRACK BY CAUSTICS

An experimental technique for determining the anti plane stress intensity factor K Ⅲ of a three dimensional crack, which is very difficult to obtain by other experimental methods, has been presented by using reflected caustics in combination with the stress freezing and stress releasing technique. The results of this experimental method coincided favorably with the theoretical analysis results of Tweed and Rooke.

An experimental study of the dynamic features of shadow areas of caustics in response to loading/unloading fracture

Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area.

Effect of the Relative Position with Gaussian Beam Center and Droplet Center on Optical Caustics

In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics of drops with an equatorial radius a = 50 μm, 100 μm, 200 μm, and 500 μm are studied at the same drop/beam ratios (i.e. γ the ratio between the droplet equatorial radius and the Gaussian beam waist) using concentric illumination with a Gaussian beam, and the effect of droplet size on the optical caustics is analyzed. The curvature of the rainbow fringe and the evolution of the cusp caustics position, in this case, are obtained;the diameter range of droplet shape (ellipsoid) measured by Gaussian beam illumination is broadened. Based on this model, the effects of the relative positions d = 0, 0.5yR, and yR on the optical caustics of the droplet when the center of the Gaussian beam deviates from the droplet center (the center of the Gaussian beam waist is on the same y-axis as the droplet center) are discussed. The optical caustics of the droplet when the center of the Gaussian beam is off the droplet center (the center of the Gaussian beam waist is on the z-axis with the droplet center) are also discussed. The effects of the relative positions of the center of the beam waist and the droplet center d = 0, 0.5yR, and yR on the optical caustics are also discussed. A method of measuring droplet shape with Gaussian beam illumination is proposed when the beam waist center is coaxial with the droplet center.

Ingestion of Caustics by Children in Brazzaville (CONGO)

Ingestion of caustics by children is serious because of the increase in their frequency and the difficulties due to their management. Objective: To improve the management of caustic lesions in Pediatric Department at the University Hospital of Brazzaville. Patients and Methods: Prospective study was conducted from January 2014 to December 2015 in the Pediatric Departments of the UHB and centers of digestive endoscopy in Brazzaville. All children who ingested a caustic product and hospitalized were included after obtaining parental’s consent. The studied parameters were: Age, sex, nature and quantity of the caustic, the family’s attitude, clinical signs, endoscopic results according to Zagar’s classification, therapeutic modalities and evolution. Results: 8292 children were hospitalized and 68 because of the ingestion of caustic, a frequency of 0.8%. The average age was 23.6 months [2 months - 16 years]. The male sex was predominant (57.4%). Ingestion was accidental in 88.2% and voluntary in 11.8%. Factors favoring ingestion were storage methods (81.5%) and parental’s inattention or negligence (10.8%). Bleach was the most incriminated caustic (54.4%) followed by caustic soda (29.4%). The estimated quantity ingested was assumed to be minimal in 61.7%. Unsuitable acts were practiced by the family before the medical consultation in 66.1%. The dominant symptoms were digestive (47%) and neurological (25%). The average time to perform endoscopy was 48 hours in 88.2%. Endoscopy revealed lesions in 51.7%, the different stages were I (12 cases), II (16 cases) and III (3 cases). The mains factors of gravity were inappropriate gestures (85%) and the non-respect of the fasting (9%). Proton pump inhibitors were used in 50%. The evolution was favorable for in 73.5%. Conclusion: Ingestion of caustics by children is most often accidental favored by the inadequate packaging and storage. Prevention is about educating people in order to reduce their frequency.

Death from caustic ingestion:A case report

Rationale:Acute caustic ingestion from suicidal intent is not usual in emergency departments in developed countries.One of the substances commonly ingested by suicidal patients,phosphoric acid,tends to cause multi-system derangements.Patient’s Concern:A 41-year-old male patient presented with complaints of throat discomfort,severe generalized abdominal pain,and multiple episodes of hematemesis after ingesting a restroom cleaning solution.Diagnosis:Poisoning by acute caustic ingestion(containing<30%phosphoric acid and<4%ethylene glycol).Interventions:The patient was administered 50 mL of 8.4%sodium bicarbonate solution followed by an isotonic sodium bicarbonate solution running at 500 mL/h,a hyperkalemia kit,ceftriaxone,metronidazole,omeprazole,and atropine.The patient then underwent urgent hemodialysis.Outcomes:The patient suffered gastrointestinal bleeding as a result of local caustic injury.In addition,his course of illness was complicated by severe acidemia from high anion gap metabolic acidosis and deranged electrolytes(hyperphosphatemia,hyperkalemia,and hypocalcemia).He developed multi-organ failure and eventually demised.Lessons:The clinician needs to be mindful of the multi-system complications arising from such a caustic ingestion.These patients need to be monitored closely for deterioration,and have prompt management of the various arising complications,to reduce the high morbidity and mortality associated with this condition.

Caustics of developable surfaces

While considering a mirror and light rays coming either from a point source or from infinity,the reflected light rays may have an envelope,called a caustic curve.In this paper,we study developable surfaces as mirrors.These caustic surfaces,described in a closed form,are also developable surfaces of the same type as the original mirror surface.We provide efficient,algorithmic computation to find the caustic surface of each of the three types of developable surfaces(cone,cylinder,and tangent surface of a spatial curve).We also provide a potential application of the results in contemporary free-form architecture design.

Accidental Ingestion of Nitric Acid in an Agricultural Company: A Case Study and Literature Review

Introduction: Though common in society, caustic accidental ingestion is rare in the agricultural industry. This study describes a case of ingestion of nitric acid used as an agricultural fertilizer by an ordinary worker at the Société de Cultures Légumières. Clinical Case: This is a 33-year-old unschooled woman who ingested a sip of nitric acid from an abandoned labelled acid canister near a farming plot of land. She showed a burn of the oral cavity with a bleeding tablecloth and an intense retrosternal pain. The duodenal oesophagus fibroscopy screening that was carried out 18 hours after the accident, revealed an esophagitis class 2b. The tests revealed no anomalies. Fifteen (15) days after the accident, the FOGD was normal. Following an 8-month-follow up, no signs of stenosis or degeneration were noted. Conclusion: The accidental ingestion of nitric acid is rare in adult. Its treatment is mainly symptomatic and aims at preserving vital functions without directly fighting the ingested substance off. The right actions must be integrated into the 15-minute Health and Safety awarenesssessions for optimum pre-hospital management. The hospital evaluation is mandatory and is carried out thanks to the digestive endoscopy, which is still relevant in this indication, but is completed by the thoraco-abdominal CT. The latter is very sensitive the transmural necrosis diagnosis.

Changing trends in the minimally invasive surgery for corrosive esophagogastric stricture

Esophagogastric stricture is the troublesome long-term complication of corrosive ingestion with a significant adverse impact on the quality of life.Surgery remains the mainstay of therapy in patients where endoscopic treatment is not feasible or fails to dilate the stricture.Conventional surgical management of esophageal stricture is open esophageal bypass using gastric or colon conduit.Colon is the commonly used esophageal substitute,particularly in those with high pharyngoesophageal strictures and in patients with accompanying gastric strictures.Traditionally colon bypass is performed using an open technique that requires a long midline incision from the xiphisternum to the suprapubic area,with adverse cosmetic outcomes and long-term complications like an incisional hernia.As most of the affected patients are in the second or third decade of life minimally invasive approach is an attractive proposition.However,minimally invasive surgery for corrosive esophagogastric stricture is slow to evolve due to the complex nature of the surgical procedure.With advancements in laparoscopic skills and instrumentation,the feasibility and safety of minimally invasive surgery in corrosive esophagogastric stricture have been documented.Initial series have mainly used a laparoscopic-assisted approach,whereas more recent studies have shown the safety of a total laparoscopic approach.The changing trend from laparoscopic assisted procedure to a totally minimally invasive technique for corrosive esophagogastric stricture should be carefully disseminated to preclude adverse longterm outcomes.Also,well-designed trials with long-term follow-ups are required to document the superiority of minimally invasive surgery for corrosive esophagogastric stricture.The present review focuses on the challenges and changing trends in the minimally invasive treatment of corrosive esophagogastric stricture.

Endoscopic Aspects of Caustic Injuries of the Upper Gastrointestinal Tract in Parakou, Benin Republic: A Multicenter Study

Objective: Caustic ingestion is a medico-surgical emergency. The objective of this study is to describe endoscopic lesions of the upper gastrointestinal tract secondary to caustic ingestion in Parakou, Benin Republic. Patients and Methods: This was a retrospective and descriptive cross-sectional study. The study was multicenter in the gastrointestinal endoscopy units of the Teaching Hospital Center of Borgou-Alibori and the Military Teaching Hospital of Parakou. It covered the period from July 2015 to October 2021. This included any patient who ingested a caustic substance and performed a gastroscopy in one of the two endoscopy units. The variables studied were: socio-demographic data, the nature of the caustic substance ingested, the time between the caustic ingestion and the performance of gastroscopy and injuries of the upper gastrointestinal tract. Results: Out of the 24 patients included, 19 were men, i.e. a sex ratio of 3.8. Their average age was 25.54 ± 12.04 years with extremes of 6 and 50 years. Five subjects (20.83%) were under the age of 18 and the ingestion was accidental in them. Among the 19 patients aged at least 18 years, caustic ingestion was voluntary in 14 (73.68%). The caustic substance ingested was either a base (sodium hydroxide or caustic soda) or an acid (sulfuric acid) in 14 cases (58.33%) and 10 cases (41.67%), respectively. The time between the caustic ingestion and the performance of gastroscopy varied from 1 to 1095 days. The endoscopic lesions objectified were: stenosis (37.5%), ulcerations (29.17%), necrosis (20.83%), or erythema (12.25%). Conclusion: In Parakou, caustic ingestion, usually bases, is often voluntary in adult men. Endoscopic lesions were often ulcerative but sometimes necrotic.

Accidental ingestion of foreign bodies/harmful materials in children from Bahrain:A retrospective cohort study

BACKGROUND Children like to discover their environment by putting substances in their mouths.This behavior puts them at risk of accidentally ingesting foreign bodies(FBs)or harmful materials,which can cause serious morbidities.AIM To study the clinical characteristics,diagnosis,complications,management,and outcomes of accidental ingestion of FBs,caustics,and medications in children.METHODS We conducted a retrospective cohort study of all children admitted for accidental ingestion to the Department of Pediatrics,Salmaniya Medical Complex,Bahrain,between 2011 and 2021.Demographic data,type of FB/harmful material ingested,and investigations used for diagnosis and management were recorded.The patients were divided into three groups based on the type of ingested material(FBs,caustics,and medications).The three groups were compared based on patient demographics,socioeconomic status(SES),symptoms,ingestion scenario,endoscopic and surgical complications,management,and outcomes.The FB anatomical location was categorized as the esophagus,stomach,and bowel and compared with respect to symptoms.The Fisher’s exact,Pearson’s χ^(2),Mann-Whitney U,and Kruskal-Wallis tests were used for comparison.RESULTS A total of 161 accidental ingestion episodes were documented in 153 children.Most children were boys(n=85,55.6%),with a median age of 2.8(interquartile range:1.8-4.4)years.Most participants ingested FBs(n=108,70.6%),31(20.3%)ingested caustics,and the remaining 14(9.2%)ingested medications.Patients with caustic ingestion were younger at the time of presentation(P<0.001)and were more symptomatic(n=26/31,89.7%)than those who ingested medications(n=8/14,57.1%)or FBs(n=52/108,48.6%)(P<0.001).The caustic group had more vomiting(P<0.001)and coughing(P=0.029)than the other groups.Most FB ingestions were asymptomatic(n=55/108,51.4%).In terms of FB location,most esophageal FBs were symptomatic(n=14/16,87.5%),whereas most gastric(n=34/56,60.7%)and intestinal FBs(n=19/32,59.4%)were asymptomatic(P=0.002).Battery ingestion was the most common(n=49,32%).Unsafe toys were the main source of batteries(n=22/43,51.2%).Most episodes occurred while playing(n=49/131,37.4%)or when they were unwitnessed(n=78,57.4%).FBs were ingested more while playing(P<0.001),caustic ingestion was mainly due to unsafe storage(P<0.001),and medication ingestion was mostly due to a missing object(P<0.001).Girls ingested more jewelry items than boys(P=0.006).The stomach was the common location of FB lodgment,both radiologically(n=54/123,43.9%)and endoscopically(n=31/91,34%).Of 107/108(99.1%)patients with FB ingestion,spontaneous passage was noted in 54(35.5%),endoscopic removal in 46(30.3%),laparotomy in 5(3.3%)after magnet ingestion,and direct laryngoscopy in 2(1.3%).Pharmacological therapy was required for 105(70.9%)patients;79/105(75.2%)in the FB group,22/29(75.9%)in the caustic group,and 4/14(28.8%)in the medication group(P=0.001).Omeprazole was the commonly used(n=58;37.9%)and was used more in the caustic group(n=19/28,67.9%)than in the other groups(P=0.001).Endoscopic and surgical complications were detected in 39/148(26.4%)patients.The caustic group had more complications than the other groups(P=0.036).Gastrointestinal perforation developed in the FB group only(n=5,3.4%)and was more with magnet ingestion(n=4)than with other FBs(P<0.001).In patients with FB ingestion,patients aged<1 year(P=0.042),those with middle or low SES(P=0.028),and those with more symptoms at presentation(P=0.027)had more complications.Patients with complications had longer hospital stays(P<0.001)than those without.CONCLUSION Accidental ingestion in children is a serious condition.Symptomatic infants from middle or low SES families have the highest morbidity.Prevention through parental education and government legislation is crucial.

Experimental study on dynamic fracture behavior of three-point bending beam with double deformity inclusions

The dynamic fracture behavior of the three-point bending beam with double deformity inclusions under impact loading is studied by using digital high-speed photography in combination with the transmission-type dynamic caustic method. The experimental results indicate that the fluctuation of crack propagation velocity v first increases and then decreases in the crack propagation process. During the process of crack propagating into the inclusion area, the fracture resistance effect of the circular inclusion is the most significant and the effects of triangular and square inclusions are less obvious. The stress intensity factor near the crack tip increases during the propagation process and reaches its maximum value when the crack tip is close to the inclusions. The crack tip’s dynamic stress intensity factor （ DSIF） decreases when the crack exceeds the middle area of the double inclusions. These results provide an experimental basis and scientific foundation to strengthen the evaluation and fracture analysis of the structure containing deformity inclusions.

Therapeutic upper gastrointestinal tract endoscopy in Paediatric Gastroenterology

Since the first report of use of endoscopy in children in the 1970 s, there has seen an exponential growthin published experience and innovation in the field. In this review article we focus on modern age therapeutic endoscopy practice, explaining use of traditional as well as new and innovative techniques, for diagnosis and treatment of diseases in the paediatric upper gastrointestinal tract.

INFLUENCE OF LOADING RATE ON DYNAMIC FRACTURE BEHAVIOR OF FIBER-REINFORCED COMPOSITES

The effect of loading rate on the dynamic fracture properties and the failure mechanisms of glass fiber-reinforced composite materials under mode I fracture is studied. Dynamic reflective caustic experiments are carried out for two loading rates. By measuring the characteristic dimensions of the shadow spots during the caustic experiments, the dynamic SIFs are calculated for different loading rates. The experimental results indicate that the dynamic fracture toughness Kid increases remarkably with increasing loading rate, and the crack grows faster under the high-velocity impact. Moreover, by examining the crack growth routes and the fracture surfaces, it is shown that the loading rate also greatly affects the failure mechanisms at micro-scale.

EXPERIMENTAL STUDY ON CRACK CURVING PROPAGATION IN BENDING BEAMS UNDER IMPULSIVE LOAD

Dynamic fracture behaviour of crack curving in bent beams has been investigated. In order to understand the propagation mechanism of such cracks under impact, an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack. From the state change of the transient stresses in polymer specimen, the curving fracture in the impulsively loaded beams is analyzed. The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.