Search Results (4)

Environmental sustainability and eco-efficiency stand as imperative benchmarks for the upcoming era of materials. The use of sustainable plant fiber composites (PFCs) in structural components has garnered significant interest within industrial community. The durability of PFCs is an important consideration and needs to be well understood before their widespread application. Moisture/water aging, creep properties, and fatigue properties are the most critical aspects of the durability of PFCs. Currently, proposed approaches, such as fiber surface treatments, can alleviate the impact of water uptake on the mechanical properties of PFCs, but complete elimination seems impossible, thus limiting the application of PFCs in moist environments. Creep in PFCs has not received as much attention as water/moisture aging. Existing research has already found the significant creep deformation of PFCs due to the unique microstructure of plant fibers, and fortunately, strengthening fiber-matrix bonding has been reported to effectively improve creep resistance, although data remain limited. Regarding fatigue research in PFCs, most research focuses on tension-tension fatigue properties, but more attention is required on compression-related fatigue properties. PFCs have demonstrated a high endurance of one million cycles under a tension-tension fatigue load at 40% of their ultimate tensile strength (UTS), regardless of plant fiber type and textile architecture. These findings bolster confidence in the use of PFCs for structural applications, provided special measures are taken to alleviate creep and water absorption. This article outlines the current state of the research on the durability of PFCs in terms of the three critical factors mentioned above, and also discusses the associated improvement methods, with the hope that it can provide readers with a comprehensive overview of PFCs’ durability and highlight areas worthy of further research. Full article

Observations are reported in uniaxial tensile tests with various strain rates, tensile relaxation tests with various strains, and tensile creep tests with various stresses on high-density polyethylene (HDPE) at room temperature. Constitutive equations are developed for the viscoelastoplastic response of semicrystalline polymers. The model involves seven material parameters. Four of them are found by fitting observations in relaxation tests, while the others are determined by matching experimental creep curves. The predictive ability of the model is confirmed by comparing observations in independent short- and medium-term creep tests (with the duration up to several days) with the results of numerical analysis. The governing relations are applied to evaluate the lifetime of HDPE under creep conditions. An advantage of the proposed approach is that it predicts the stress-time-to-failure diagrams with account for the creep endurance limit. Full article

Knowledge of the properties and behavior of materials under certain working conditions is the basis for the selection of the proper material for the design of a new structure. This paper deals with experimental investigations of the mechanical properties of unalloyed high quality steel S235JRC + C (1.0122) and its behavior under conditions of high temperatures, creep and mechanical fatigue. The response of the material at high temperatures (20–700 °C) is shown in the form of engineering stress-strain diagrams while that at creep behavior (400–600 °C) is shown in the form of creep curves. Furthermore, based on uniaxial fully reversed mechanical fatigue tests ($R=-1$), a stress-life (S-N) fatigue diagram has been constructed and the fatigue (endurance) limit of the material is calculated The experimentally determined value of tensile strength at room temperature is 534 MPa. The calculated value of the fatigue limit, also at room temperature, using the modified staircase method and based on the mechanical fatigue tests data, is 202 MPa. With regard to creep resistance, steel 1.0122 can be considered creep-resistant only at a temperature of 400 °C and at an applied stress not exceeding 50% of the yield strength corresponding to this temperature. Full article

This paper presents the high-temperature creep-fatigue testing of a Ni-based superalloy of Alloy 617 base metal and weldments at 900 °C. Creep-fatigue tests were conducted with fully reversed axial strain control at a total strain range of 0.6%, 1.2%, and 1.5%, and peak tensile hold time of 60, 180, and 300 s. The effects of different constituents on the combined creep-fatigue endurance such as hold time, strain range, and stress relaxation behavior are discussed. Under all creep-fatigue tests, weldments’ creep-fatigue life was less than base metal. In comparison with the low-cycle fatigue condition, the introduction of hold time decreased the cycle number of both base metal and weldments. Creep-fatigue lifetime in the base metal was continually decreased by increasing the tension hold time, except for weldments under longer hold time (>180 s). In all creep-fatigue tests, intergranular brittle cracks near the crack tip and thick oxide scales at the surface were formed, which were linked to the mixed-mode creep and fatigue cracks. Creep-fatigue interaction in the damage-diagram (D-Diagram) (i.e., linear damage summation) was evaluated from the experimental results. The linear damage summation was found to be suitable for the current limited test conditions, and one can enclose all the data points within the proposed scatter band. Full article