EFFECT OF RIPPLE LOAD ON THE STRESS-CORROSION CRACKING IN STRUCTURAL STEELS
The presence of small ripple loading can, under certain circumstances, significantly reduce time-to-failure and threshold stress intensity for stress-corrosion cracking (SCC) of steels. A predictive framework for such ripple-loading effects (RLE) is developed from concepts and descriptors used in SCC and corrosion fatigue characterisation. The proposed framework is capable of defining critical conditions required for the occurrence of RLE and predicting time-to-failure curves. The agreement between the predicted and laboratory data is excellent.
Computer-Controlled Stress Intensity Gradient Technique for High Rate Fatigue Crack Growth Testing
An automated test system utilizing a computer for data acquisition and machine control was used to obtain crack growth rate data from 2.5 × 10−8 to 2.5 × 10−6 m/cycle (1 × 10−6 to 1 × 10−4 in./cycle) on a compact type specimen. The crack length was monitored continuously by using the elastic compliance technique, enabling the stress intensity K to be increased according to the equation ΔK = ΔK exp [C(a − a0)] (where a0 and a are the initial and instantaneous crack lengths and C is a test variable). Crack growth data were obtained on a Ni-Cr-Mo-V rotor steel by using both different, programmed K gradients and the more conventional constant-load-amplitude method where the stress intensity increases as a function of increasing crack length. Excellent agreement was observed between the two test procedures.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.