The removal of thermally aged films of triacylglycerides by surfactant solutions

Thermal ageing of triacylglycerides (TAG) at high temperatures produces films which resist removal using aqueous surfactant solutions. We used a mass loss method to investigate the removal of thermally aged TAG films from hard surfaces using aqueous solutions of surfactants of different charge types. It was found that cationic surfactants are most effective at high pH, whereas anionics are most effective at low pH and a non-ionic surfactant is most effective at intermediate pH. We showed that the TAG film removal process occurs in several stages. In the first ‘‘lag phase’’ no TAG removal occurs; the surfactant first partitions into the thermally aged film. In the second stage, the TAG film containing surfactant was removed by solubilisation into micelles in the aqueous solution. The effects of pH and surfactant charge on the TAG removal process correlate with the effects of these variables on the extent of surfactant partitioning to the TAG film and on the maximum extent of TAG solubilisation within the micelles. Additionally, we showed how the TAG removal is enhanced by the addition of amphiphilic additives such as alcohols which act as co-surfactants. The study demonstrates that aqueous surfactant solutions provide a viable and more benign alternative to current methods for the removal of thermally aged TAG films

Effect of mean stress on multiaxial ratcheting life: a simplified life prediction model based on average equivalent stress amplitude

This article proposes a model to predict uniaxial and multiaxial ratcheting life by addressing the three primary parameters that influence failure life: fatigue damage, ratcheting damage and the multiaxial loading path. These three factors are addressed in the present model by (a) the stress amplitude for fatigue damage, (b) mean stress-dependent Goodman equation for ratcheting damage and (c) an inherent weight factor based on average equivalent stress to account for the multiaxial loading. The proposed model requires only two material constants which can be easily determined from uniaxial symmetric stress-controlled fatigue tests. Experimental ratcheting life data collected from the literature for 1025 and 42CrMo steel under multiaxial proportional and nonproportional constant amplitude loading ratcheting with triangular sinusoidal and trapezoidal waveform (i.e. linear, rhombic, circular, elliptical and square stress paths) have shown good agreement with the proposed model

Microstructural analysis of pre-strained TRIP steel after fatigue testing

The widespread introduction of multiphase sheet steels in the automotive industry has led to considerable interest in the fatigue properties of these materials. The different microstructural phases within matelials such as TRIP steels can influence the fatigue behaviour due to the manner in which the cyclic strain is accommodated within these phases. In this study fully reversed straincontrolled fatigue tests were perfonnrmed on a commercially-produced uncoated TRIP 780 steel both in the as-received and 20 % prestrained condition. The pre-strained TRIP steel showed significant cyclic softening at higher strain amplitudes, whereas some initial work hardening was observed at lower strain amplitudes before cyclic softening. The cyclic stabilised strength of the pre-strained TRIP steel was independent of strain amplitude, while the cyclic stabilised strength of the as-received TRIP steel increased with strain amplitude. Transmission Electron Microscopy TEM was used to examine the effect of the cyclic deformation on the microstructure of the different conditions, with the differences in fatigue behaviour explained based on the differences in the deformation structure formed within the steel (i.e. dislocation density and sub-structure and microband formation).<br /