Torsional Shear Strength Tests for Glass–Ceramic Joined Silicon Carbide

Abstract

A torsion test on hour‐glass‐shaped samples with a full joined or a ring‐shaped joined area was chosen to measure shear strength of glass–ceramic joined silicon carbide. Shear strength of about 100 MPa was measured for full joined SiC with fracture completely inside their joined area. Attempts to obtain this shear strength with a ring‐shaped joined area failed due to mixed mode fractures. On the contrary, full joined and ring‐shaped steel hour‐glasses joined by a glass–ceramic gave the same shear strength, thus suggesting that this test measures shear strength of joined components only when their fracture is completely inside their joined area.

Modeling and testing miniature torsion specimens for SiC joining development studies for fusion

“…The PNNL joints, which are synthesized using displacement reactions between TiC and Si, are observed to fail out-of-plane, or in the base SiC material, during torsion testing [1], similar to what others had observed for high-strength joints [20,22,23]. Most of the types of joints reported in Ref.…”

“…In addition, these test specimens are all quite large, or conversely are not miniature-type tests, whereas irradiation volumes are small and demand miniature specimen designs. The miniature torsion geometry, therefore, was designed to provide a test specimen consistent with small irradiation test volumes associated with in-reactor irradiation testing [3,8,[20][21][22][23][24] and to provide a more consistent shear strength test. The experimental data for some joint configurations revealed excellent data reliability and reduced data scatter [21,24] for this specimen design.…”

“…The experimental data for some joint configurations revealed excellent data reliability and reduced data scatter [21,24] for this specimen design. However, recent high-strength joints fabricated for SiC and SiC-composites have revealed that this test specimen design also has some problems [20,22,23], namely out-ofplane fractures that fail to provide simple shear strength values. Since the miniature torsion test appears to be reliable under certain conditions, but not others, and since this design is ideal for testing many joints in a small irradiation volume, a mechanical model of this joint was created to help understand the observed shear failures under a range of simulated conditions.…”

Mechanical behavior of SiC joints brazed using an active Ag‐Cu‐In‐Ti braze at elevated temperatures

“…Bending test is a good tool to characterize the behavior of the joint at high temperatures, but the measurement of the shear strength without the contribution of any other force in the joining area is fundamental to perform a full joint characterization . Therefore, the use of a torsional shear test is of importance as it only contains torsional shear stresses on the joints . With the torsional shear apparatus, it was not possible to characterize the joint accurately below 450°C as the samples always broke in the ceramic partner, an example is shown in Figure .…”

“…36 Therefore, the use of a torsional shear test is of importance as it only contains torsional shear stresses on the joints. 37 With the torsional shear apparatus, it was not possible to characterize the joint accurately below 450°C as the samples always broke in the ceramic partner, an example is shown in Figure 8. This is due to a combination of the accumulation of very high localized stresses at contact points where the shear load is transferred and the low K Ic of the material, initiating fracture in the ceramic.…”