Dynamic material testing system having independent control over specimen deformation and strain rate and a method for use therein

In a material testing system, apparatus for controllably deforming a specimen comprising:

• force producing means, having a first servo-controlled hydraulic cylinder and mounted to a fixed frame, for controllably generating a mechanical force along a first pre-defined direction;
• said frame having first and second cross heads spaced apart and electrically and mechanically connected together, in a fixed arrangement, by first and second conductive columns, said first and second cross-heads having first and second holes extending therethrough in said first pre-defined direction and a first insulating bearing lining said first hole;
• first and second deforming means for compressively deforming a speciment so as to generate a compressive deformation therein, wherein said first and second deforming means comprise first and second electrically conductive anvils which abuttingly engage with corresponding opposing sides of said specimen while the specimen is being deformed;
• force transferring and stopping means, situated in abutting engagement with said first deforming means, for moving said first deforming means, in response to said force, along said first pre-defined direction so as to compressively deform said specimen and for terminating further movement of said first deforming means as soon as said first deforming means has compressed said specimen by a pre-determined amount;
• said force transferring and stopping means comprising:
• a cross bar having two opposing ends and fixedly connected to said first and second pistons in the vicinity of the two opposing ends thereof, for establishing and maintaining, in response to a force exerted thereon by said pair of cylinders, an electrical current path through said specimen, said cross bar further having a coupler for abuttingly engaging with a corresponding coupler attached to an end of a piston of said first cylinder and transferring the mechanical force produced therefrom to said specimen so as to produce the compressive deformation thereof;
• an insulating plate fixedly connected at one surface of said plate at substantially a center axial location thereof to said cross bar;
• first and second conductive extension shafts, said first extension shaft extending through the first insulating bearing located in said first cross-head so as to be electrically insulated from said first cross head;
• a rigid conductor fixedly and electrically connected between a second surface of said insulating plate, opposite to said first surface thereof, and a first end of said first extension shaft;
• a substantially U-shaped cross stop having a third hole located axially therethrough and a second bearing lining said third hole for guiding said second shaft along said first and second directions but electrically insulating said second shaft from said cross head;
• a stop plate fixedly secured to a first end of said second shaft and situated between a second end of said first shaft and the first end of said second shaft, wherein the stop plate has a diameter greater than that of the third hole and functions to impact against said cross stop during movement of said second shaft in the first direction so as to abruptly halt further movement of said second shaft in said first direction during compressive deformation of said specimen;
• and
• first and second stop bars fixedly securing, through corresponding first and second insulating spacers, said cross stop to the second cross head;
• moving means, having a second servo-controlled hydraulic cylinder and coupled to said second deforming means and mounted to the fixed frame, and operative in response to the second hydraulic cylinder, for moving said specimen and said first and second deforming means by the pre-determined amount and in a second direction opposite to the first pre-defined direction prior to commencement of said compressive deformation, wherein said moving means experiences substantially no movement in said first pre-defined direction while said specimen is being compressively deformed;
• said moving means comprising:
• a wedge shaft connected at one end to said second deforming means and extending in said first direction therefrom;
• a wedge having a first inclined surface;
• a wedge guide fixedly connected to said frame for guiding movement of said wedge along third and fourth directions, said third and fourth directions being opposite to each other and substantially perpendicular to said first and second directions;
• a wedge yoke connected to said wedge shaft at a second end thereof and having a second inclined surface complementary to said first inclined surface for slidably engaging with said first inclined surface so as to move said wedge yoke in either said first or second directions as said wedge yoke is moved in said third or fourth directions, wherein said wedge yoke moves at a pre-defined proportion of distance and rate at which said wedge moves while in sliding engagement therewith;
• and
• wherein the second hydraulic cylinder is connected to said wedge at one end thereof for controllably moving said wedge through a desired distance in either said third or fourth directions;
• and
• wherein the first anvil is securely mounted to a second surface of said second extension shaft;
• and wherein said first and second extension shafts, said stop plate and said anvil are in substantial coaxial alignment;
• whereby strain rate and final strain induced in the specimen during said compressive deformation are respectively and substantially independently determined by velocity of said force transferring and stopping means along said first direction during said deformation and a distance that said moving means is moved in said second pre-defined direction prior to said deformation.

In a dynamic thermal-mechanical material testing system, a method for simultaneously imparting pre-defined thermal and deformation profiles to a test specimen, comprising the steps of:

• imparting a mechanical deformation to a specimen comprising:
• controllably generating, through a first actuator mounted to a fixed frame, a mechanical force along a first pre-defined direction;
• compressively deforming the specimen, using first and second deforming means, so as to generate a compressive deformation therein, wherein said first and second deforming means abuttingly engage with corresponding opposing sides of said specimen while the specimen is being deformed;
• first moving said first deforming means, in response to said force, along said first pre-defined direction so as to compressively deform said specimen and terminating further movement of said first deforming means as soon as said first deforming means has compressed said specimen by a pre-determined amount;
• and
• second moving, using a wedge assembly coupled to both said second deforming means and mounted to the fixed frame and having a second actuator, said specimen and said first and second deforming means by the pre-determined amount and in a second direction opposite to the first pre-defined direction prior to commencement of said compressive deformation;
• and
• imparting a thermal profile to said specimen substantially simultaneously with said mechanical deformation comprising:
• establishing an electrical current path through said specimen prior to the commencement of said compressive deformation;
• and
• passing a controlled amount of electrical current through said path at least while said compressive deformation is occurring so as to self-resistively heat said specimen in order to generate both a desired heating rate and isothermal planes at a desired corresponding temperature substantially throughout a work zone of the specimen.