FEA and testing
Tensile tests were carried out on four carabiners. The aim of the testing was to determine the failure locations and failure loads. This information could then be used to verify FEA stress testing. In addition, the location of failure and the failure load can be used to judge the accuracy of the assumption that a carabiner fails in pure tension.
Longitudinal, closed gate tensile tests were carried out according EN12275 on two Black Diamond Light D and two Black Diamond Hotwire carabiners. Failure locations can be seen in figure 30 - failure occurs consistently where the carabiner arms connect to the spine.
Figure 30: Two Black Diamond Light D (left) and two Black Diamond Hotwire (right) carabiners were tested to failure.
The failure loads of the Light D carabiners were 28.0 kN and 29.1 kN. The failure loads of the Hotwire carabiners were 28.8 kN and 29.1 kN. The cross-section area of a Light D carabiner is 7.17 x10 -5 m 2 . Taking an average failure load of 28.55kN, if it is assumed that the load is taken entirely by the spine, this would result in a stress of 398 MPa in the spine. The tensile strength of the carabiner material is around 510 MPa, so the stress in the spine is 112 MPa higher than if the spine was in pure tension. This suggests that the bending of the carabiner arm plays a significant role the carabiner strength.
A CAD model of a Black Diamond Light D carabiner was created in SolidWorks and FEA stress analysis was carried out using CosmosWorks. The Light D geometry was recreated using data from Black Diamond and overlaying an image of a Light D carabiner onto a sketch in Solidworks.
Figure 31: Stress analysis was carried out on a model of a Black diamond Light D carabiner using CosmosWorks.
The CAD model was meshed, material property data for aluminium 7075 T6 was entered and forces and constraints were applied. On one end, the carabiner was constrained for translation in three orthogonal axes to represent a fixed pin contact (see figure 31). On the other end it was constrained in two orthogonal directions perpendicular to the spine - to represent a moving tensile test pin. The model represented the carabiner in its open gate configuration. A force of 7 kN was applied, in the direction of the spine, on the less constrained of the two surfaces. A simulation was run and this resulted in maximum stresses at the constraint points and stresses of a similar magnitude on the inner surface where the arms connect to the spine. This shows some agreement with the tensile tests performed as initial yielding occurred at the test pin contact points and then breakage occurred at the arm/spine connecting point. However, the stress at this point was estimated as 630 MPa. The black diamond Light D carabiner has an open gate strength rating of 7 kN, and the carabiner material has a strength of 510 MPa - this suggests that the FEA analysis is overestimating the stress in the carabiner. Once configured correctly this analysis could be used to optimise the carabiner design proposed in the design section. However, this is beyond the scope of this report.