The connection between load distribution and fracture load in the diametral compression test. An experimental study.
Dental stone specimens (diameter 41,5 mm, length 14,0 mm) manufactured with water/powder ratios 0.22 (unimpregnated and polymethylmethacrylate-impregnated specimens) and 0.30 were loaded by direct contact with the platens of the testing device and with interposed soft paddings of varying thickness and width. To ensure an even load distribution, in some experiments, inserts of aluminium with one side vaulted were inserted next to the platens. The experiments showed that: - if strip shaped paddings were inserted which were as wide as the contact surface formed on direct contact, the load required for fracture did not change; - if the contact surfaces were reduced by means of strip-shaped paddings, fracture load was considerably reduced even for small changes in the load bearing area; - if the contact surface was increased, by means of wide paddings or vaulted inserts, the fracture load also increased. The results could not be explained on the basis of statistical fracture theories. This conclusion was supported by some experiments with miniature specimens. A probabel explantation would, however, be that below a critical load distribution parasitic stresses are generated which entail fractures with fracture patterns which do not distinctively deviate from what previously has been considered as typical for valid tensile fractures.
D002133:Calcium Sulfate / Q000032:analysis*; D008768:Methylmethacrylates / Q000032:analysis; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength
D008768:Methylmethacrylates; D002133:Calcium Sulfate