Indeed, fracture or breakdown studies might be the oldest physical science studies, which still remain intriguing and very much alive. Leonardo da Vinci, more than 500 years ago, observed that the tensile strengths of nominally identical specimens of iron wire decrease with increasing length of the wires (see e.g., for a recent discussion). Similar observations were made by Galileo Galilei more than 400 years ago. This is the manifestation of the extreme statistics of failure (bigger sample volume can have larger defects due to cumulative fluctuations where failures nucleate and induce lower strength of the sample). Types
There are two types of fractures: brittle and ductile fractures respectively without or with plastic deformation prior to failure. Brittle
In brittle fracture, no apparent plastic deformation takes place before fracture. Brittle fracture typically involves little energy absorption and occurs at high speeds—up to 2,133.6 m/s (7,000 ft/s) in steel. In most cases brittle fracture will continue even when loading is discontinued.In brittle crystalline materials, fracture can occur by cleavage as the result of tensile stress acting normal to crystallographic planes with low bonding (cleavage planes). In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, with cracks proceeding normal to the applied tension.
Signs and symptoms
Signs and symptoms of familial dysautonomia usually commence during infancy and worsen with age, and may include: gastrointestinal dysmotility (including erratic gastric emptying, gastroesophageal reflux, abnormal esophageal peristalsis, oropharyngeal incoordination), dysphagia (as poor suckling in infancy) and frequent choking/gagging, recurrent vomiting, poor weight gain/growth, delayed development (especially walking) and puberty (especially in girls), recurrent aspiration pneumonia (due to inhalation of food or vomitus) with possible secondary chronic lung disease, absence of overflow tears during crying, corneal ulcers, red skin blotches and excessive sweating (often during eating or excitement), breath-holding spells, slurred speech/nasal voice, tongue ulcers (from accidental self-injuries), hyporeflexia (variable absence of deep tendon reflexes), hypotonia, enuresis, arrhythmias, hypertension (including episodic hypertension in response to emotional stress or visceral pain), hypotension (including orthostatic hypertension with compensatory tachycardia (invariably present)), impaired (but not absent) temperature and pain perception (leading to frequent accidental injury), impaired proprioception, a smooth glossy tongue, scoliosis (with possibly secondary restrictive lung disease), abnormal gait, short stature, chronic renal failure (common), visual impairment, variable cognitive ability, characteristic facial features that develop with time, impaired vibration perception, lack of fungiform papilla of the tongue, and impaired taste perception (especially for sweetness). Autonomic crises - In children with FD, recurrent episodes of vomiting may occur. Such episodes may be triggered by physical (e.g. infection) or emotional stress, may occur every 15–20 minutes for over 24 hours, and may be accompanied with: significant hypertension, drenching sweat, breathing issues, fever, tachycardia, aspiration pneumonia, skin blotches, drooling, and negative personality change.