Test Methodology Development for Experimental Structural Assessment of ASC Planar Spring Material for Long-Term Durability

A vibration-based testing methodology has been developed that will assess fatigue behavior of the metallic material of construction for the Advanced Stirling Convertor displacer (planar) spring component. To minimize the testing duration, the test setup is designed for base-excitation of a multiplespecimen arrangement, driven in a high-frequency resonant mode; this allows completion of fatigue testing in an accelerated period. A high performance electro-dynamic exciter (shaker) is used to generate harmonic oscillation of cantilever beam specimens, which are clasped on the shaker armature with specially-designed clamp fixtures. The shaker operates in closed-loop control with dynamic specimen response feedback provided by a scanning laser vibrometer. A test coordinator function synchronizes the shaker controller and the laser vibrometer to complete the closed-loop scheme. The test coordinator also monitors structural health of the test specimens throughout the test period, recognizing any change in specimen dynamic behavior. As this may be due to fatigue crack initiation, the test coordinator terminates test progression and then acquires test data in an orderly manner. Design of the specimen and fixture geometry was completed by finite element analysis such that peak stress does not occur at the clamping fixture attachment points. Experimental stress evaluation was conducted to verify the specimen stress predictions. A successful application of the experimental methodology was demonstrated by validation tests with carbon steel specimens subjected to fully-reversed bending stress; high-cycle fatigue failures were induced in such specimens using higher-than-prototypical stresse

Experimental validation of multistep quantitative crack damage assessment for truss structures by finite element model updating

In this paper, a multistep damage quantification method has been experimentally validated by quantifying crack damage of load-carrying members of truss structures based on experimental vibration records. Damage quantifications are still challenging tasks for difficulties in interpreting response signals measured from engineering structures. Open crack depth is parameterized as a damage variable. The open crack in Euler–Bernoulli beam element is modeled by introducing local flexibility coefficients to the uncracked beam element with joint rotational flexibility. Mode shapes and natural frequencies measured from experimental modal testing of a damaged laboratory-size truss bridge are used in the finite element model updating for damage quantification. Predetermined curves derived for hollow circular sections with open crack are used to estimate crack depths from updated local flexibility coefficients. According to experimental validation test, the proposed approach is proven to be viable in quantifying crack damag