Assessment of the reinforcing ability of a composite bandage for modern pipeline repair systems

The long-term operation of pipelines, which, in many cases, exceeds their regulatory service life, causes the strain ageing of metal, as well as the appearance of local mechano-corrosive damages. In this regard, the use of composites to reinforce worn pipelines constitutes one of today’s most promising technologies. In this study, a comparative analysis was performed between the composite-reinforced steel pipe calculations that were conducted using the finite element method (FEM), and those that were conducted in accordance with the DSTU ISO 24817:2019 standard. The FEM numerical calculations were carried out using the complete factorial experiment design (consisting of three factors at three levels, with twenty-seven calculations in total). Based on the results of these calculations, a regression model was developed to assess the circular deformation of the pipe’s outer surface depending on the thickness of the bandage, the thickness of the pipe, and the internal pressure. The FEM calculations were found to be in close agreement with analytical results.

Examination of Dynamic Strain Ageing Effects during Rapid Quenching of Inconel 718 Superalloy Disc

In this work, an experimental measurement, contour method, is implemented for an after quenching IN718 forging specimen to obtain the distribution of residual stress field. A sequentially coupled thermal mechanical finite element model is developed with the similar 3D geometry of the experimental specimen and implemented the same heat transfer boundary of the rapid quenching with the experimental condition. A thermal mechanical rate dependent continuum plasticity model for IN718 alloy, with the dynamic strain ageing (DSA) effect incorporated, is developed to study the impact of DAS effect on the evolution of residual stress during rapid quenching. The modelling predictions of residual stress are in good agreement with the contour method measurements. The impact of DSA effect is further quantified, indicating that an annular high plastic strain rate region in the core part of the disc is captured during the simulation of the quenching process.

Depth-Sensing Hardness Measurements to Probe Hardening Behaviour and Dynamic Strain Ageing Effects of Iron during Tensile Pre-Deformation

This work reports results from quasi-static nanoindentation measurements of iron, in the un-strained state and subjected to 15% tensile pre-straining at room temperature, 125 °C and 300 °C, in order to extract room temperature hardness and elastic modulus as a function of indentation depth. The material is found to exhibit increased disposition for pile-up formation due to the pre-straining, affecting the evaluation of the mechanical properties of the material. Nanoindentation data obtained with and without pre-straining are compared with bulk tensile properties derived from the tensile pre-straining tests at various temperatures. A significant mismatch between the hardness of the material and the tensile test results is observed and attributed to increased pile-up behaviour of the material after pre-straining, as evidenced by atomic force microscopy. The observations can be quantitatively reconciled by an elastic modulus correction applied to the nanoindentation data, and the remaining discrepancies explained by taking into account that strain hardening behaviour and nano-hardness results are closely affected by dynamic strain ageing caused by carbon interstitial impurities, which is clearly manifested at the intermediate temperature of 125 °C.