ISO 14126 | ASTM D3410: Shear Loading Compression
Compression test with shear loadingThe ISO 14126 and ASTM D3410 standards describe the shear loading compression test on composites.
The objective of this standard test method is the determination of compressive properties in laminate planes.
For this method, the compression force is transmitted via shear forces to the specimen, which is secured in the test fixture and usually includes cap strips. Homogeneous stress distribution is achieved if there is sufficient grip-to-grip separation in the unsupported center area of the specimen.
One of the benefits provided is axial guidance of the specimen during the test, as well as the elimination of force application via the end faces. This eliminates the need for high-precision preparation of the specimen end faces.
The DIN EN 2850 standard also describes the shear loading compression test on composites (Type A).
Shear loading compression test to ISO 14126, ASTM D3410
The shear loading compression method was standardized in the 1980s in ASTM D3410 as the Celanese test fixture with conical clamping elements. However, with this original Celanese device, variations in specimen thicknesses lead to unwanted linear supports of the conical clamping elements. This problem was solved in standards DIN 65375 and DIN EN 2850 (Type A) through modified Celanese test fixtures with flat wedges.
IITRI in the US developed a similar device with column guides, which replaces the old Celanese compression fixture in the current ASTM D3410. Here, the compression specimen is also clamped in guided flat wedges of the modified Celanese test fixture.
The compression specimen is first inserted in the wedge jaws, for which a separate tool is often helpful. The wedge jaws with installed specimen are then inserted in the guided compression test kit.
During the compression test, the gripping pressure is generated with wedge action created by the axial force. This can, however, lead to movement of the wedges and thereby uneven load application on the specimen.
To determine the validity of the compression test by quantifying superimposed bending deformations (percent bending), a strain measurement is carried out with separately measuring strain gauges applied centrally on both sides. The signals of the strain gauges are then averaged for determination of the compressive strain.
With the patented hydraulic compression fixture HCCF, originally developed by IMA Dresden and available through ZwickRoell, composite compression tests can be carried out according to common shear loading compression test methods.
The HCCF offers excellent accessibility, simple handling, and fixed jaws, which remain precisely aligned with one another without slipping, even during the test .
The shear loading compression method is ideal for unidirectional composite materials with lower strengths in the direction of the fiber, and for compression tests on fabrics and multidirectional composite laminates.
For high-strength carbon-fiber-reinforced composite materials and compression tests with unidirectional laminates in the direction of the fiber (UD0°), sole shear force application is often not sufficient. It either leads to invalid failure modes (end crushing, cap strip failure) or to lower compressive strength due to non-uniform stress distribution in the free specimen area. In this case it is better to apply the combined loading compression method.
