No abstract

No abstract

The influence of low-temperature gaseous carburization on the fatigue behavior of AISI 316L austenitic stainless steel was investigated. Tension-compression axial fatigue tests were performed under ambient conditions on untreated and carburized AISI 316L. The results show that the carburized AISI 316L has a 22% higher endurance limit compared to untreated AISI 316L. Fractography investigations with scanning electron microscope (SEM) reveal that for the untreated AISI 316L fatigue cracks initiate at the surface regardless of the applied stress level. For the carburized AISI 316L fatigue cracks initiate at the surface for relatively high-level stresses; for relatively low-level stresses fatigue cracks initiate at inclusions beyond the carburized case. After carburization, the ductility in the outmost 10 μm of the carburized case has significantly reduced, leading to micro-crack occurrence during fatigue tests and associated relaxation of compressive residual stress in this region. Beyond this surface-adjacent region, no evident stress relaxation occurs due to the enhanced yield strength

The stability of fresh cement paste can be described as its ability to remain homogeneous over time. Instability in the form of sedimentation and bleeding occurs for various reasons related to the material composition. In this study, the relevant mechanisms for quantifying stability are reviewed, and a conceptual model is proposed describing the sedimentation progress in terms of bleeding (supernatant), the homogeneous zone, the variable concentration zone, and the compressible sediment zone. A sensitive hydrostatic pressure test (HYSPT) with good repeatability and without influence from evaporation was developed to describe the sedimentation process of fresh cement paste. HYSPT relies on the fact that the mainly restricted Stokesian settlement of particles causes changes in the solid fraction and the fresh density at a given height and time. The influence of the pressure detection direction and position were investigated by changing the inlet design of glass pipes. The pressure drop due to cement dissolution, chemical shrinkage, and paste structural buildup also was investigated but was found to be negligible compared to the effect of density variation due to sedimentation before setting. The sedimentation rates obtained from HYSPT measurements were found to coincide with the volume fraction variation detected via in situ measurements. The solid fraction and bleeding results were in alignment with the conceptual model.