مقاله سیستم های خبره (هوش مصنوعی)

مقاله اکسس

آشنایی با UPS(منبع تغذیه بدون وقفه)

The ability to acid etch enamel dramatically affected
the practice of dentistry and initiated the interest in
adhesive procedures.1 The development and commercial
introduction of the first composite resin followed
shortly thereafter,2 as did the definition of a
composite as a “three-dimensional combination of
at least two chemically different materials with a distinct
interface separating the components.”3 The
applications for composite resin now vary from
restoration of cavities, to reconstruction of anterior
teeth, core preparation for crowns, correction of
stains and erosion, placement of orthodontic brackets,
and cementation of dental prostheses.4

Mechanical testing
Tensile tests on specimens measuring 25 by 250
mm were conducted according to ASTM 638-90 and
flexural tests on specimens measuring 11 by 140 mm
by ASTM 790-90 at the Forest Products Laboratory
Engineering Mechanics Laboratory with load applied
perpendicular to the surface of the fiber mat. A
crosshead speed of 5 mm/min. was used. The stressstrain
curves were analyzed using a three-parameter
hyperbolic tangent model that has been shown to
accurately represent the stress-strain behavior. The
composite specimens were all tested to failure. Information
collected in the tests included tensile strength
at failure, tensile modulus, flexural strength, and
flexural modulus. Notched and unnotched highspeed
impact performance of the composites (13 by
65 mm) was evaluated by Izod impact according to
ASTIM D 256.