Fixture that Can Stretch & Twist Materials in Multiple Dimensions Simultaneously

Traditionally, the tensile and shear properties of materials are evaluated separately using uniaxial test machines. In practice, most materials are subjected to forces imposed simultaneously in multiple directions resulting in coupled responses that are quite different from the uncoupled behaviors observed from uniaxial tests. The current innovation was developed to permit the evaluation of both strength and stiffness properties of materials such as weaves (shown in the left hand figure), braids, and knits subject to combined biaxial tension and shear loadings. For fabrics constructed of two principle fiber directions, the fixture utilizes two rhombus-shaped frames connected with rotary joints. The center and right hand figures illustrate this device with a plain-woven fabric under biaxial tension and shear modes respectively. When testing a specimen with biaxial loading, four ends of the specimen are rigidly secured by the clamping mechanism. The vertices of the apparatus are attached to the crossheads of a conventional uniaxial tensile/torsion machine. Upon a movement of the vertices of the linkages toward each other, their lateral links will extend outward thereby increasing the distance between the corresponding load transfer plates of each linkage. This movement applies planar tension to the specimen. Additionally, by rotating one linkage with respect to the other, the specimen will be subjected to in-plane shear. An extension to the base patent teaches a design where differential force ratios within and between axes are possible. The data obtained by fixtures incorporating this suite of innovations will allow higher-fidelity design and analysis of structures fabricated from a variety of materials including fabrics, composites, elastomers, metals, biological tissues and others. Benefits: Performance – provides coupled mechanical properties of materials much more akin to those observed in actual use User friendliness – compatible with both coventional tension/torsion and uniaxial test machines Versatility – this one fixture efficiently does the job that normally would require the inventory of many fixtures. Application Examples: Composite preforms – helps designers model fiber placement methods to avoid fiber wrinkling during resin transfer molding Tires – many of the benefits realized by the inflatable structure practitioners are transferrable to the tire community Biomedical – connective tissues on human joints are subjected to multi-axial forces resulting in complex stress states that can be better evaluated using this tool Inflatable structures – establishes effects of pressure and shear on mechanical properties of textiles and structural integrity of seams In addition to the two patents in the Documents section Patent Application 11/401,014 is also associated.