Development of fatigue testing system for in-situ observation of stainless steel 316 by HS-AFM & SEM

Abstract

A miniature three-point bend fatigue stage for in-situ observation of fatigue microcrack initiation and growth behaviour by scanning electron microscopy (SEM) and contact mode high-speed atomic force microscopy (HS-AFM) has been developed. Details of this stage are provided along with finite element simulations of the stress profiles of said stage and specimen on loading. The proposed stage facilitates study of the micro mechanisms of fatigue damage evolution when used during SEM and HS-AFM scanning of the sample surface. High amplitude low cycle fatigue tests have been carried out on annealed AISI Type 316 stainless steel to demonstrate the applicability of the system. Characteristic features of surface topography and evolution of slip bands observed have been documented. Images obtained by SEM and HS-AFM are presented for comparison. Finally, to demonstrate the capability of the new facility combined with HS-AFM, the spacing between slip bands and their height at different grains at the centre of the metal sample are measured and compared.

Observation of stress corrosion cracking using real-time in situ high-speed atomic force microscopy and correlative techniques

“…Figure 1b shows slip bands forming at regular intervals, with differing directions in each grain either side of the GB; as each grain has a different crystallographic orientation. This phenomenon has been observed within other AFM studies of deformed austenitic stainless steels [35][36][37] . In some areas, the slip bands have two directions within a single grain, due to the activation of a second slip system, indicative of higher levels of strain, or a slip direction with a similar Schmid factor 35,37 .…”

“…Type 304 stainless steel is austenitic and so has a face centred cubic (FCC) crystallographic structure which, when stressed, produces slip on the most closely packed {111} planes 35,36 . Figure 1b shows slip bands forming at regular intervals, with differing directions in each grain either side of the GB; as each grain has a different crystallographic orientation.…”

Opportunities and Challenges for Biosensors and Nanoscale Analytical Tools for Pandemics: COVID-19

“…Typically, in AFM measurement, the deflection of microcantilever is used to probe the interaction between the surface of the sample and the nanometric tip located at the end of microcantilever. Based on the time scales, type, and range of interaction, an extensive range of information including atomistic details of the surface, mechanical, physical, chemical, thermal, and viscoelastic properties of nano/bio materials can be obtained. − The earliest invented mode of AFM was the contact mode, where the tip is raster scanned through the sample surface while maintaining a constant force applied to the sample through deflection detection by adjusting the height of the tip. The main challenges in using contact mode to image soft materials such as viruses and other biological specimens is the applied force to avoid the reversible or irreversible deformation, unwanted friction, and damage to the sample .…”

Insight into prognostics, diagnostics, and management strategies for SARS CoV-2

“…A broad information pool including mechanical, thermal, chemical, physical, atomistic details of the surface, and viscoelastic characteristics of nanobiomaterials entities could be achieved based on time scales, range, and types of interactions. [211][212][213][214][215][216][217][218][219][220][221][222][223] The very rst invented mode of AFM is "contact mode", in which the tip is raster scanned on the specimen interface by sustaining a constant force generated on the sample through deection recognition by regulating the height of the tip. However, the foremost challenge associated with contact mode utilization while imaging so entities such as biological specimens and viruses is the force (applied) to circumvent undesirable friction, impairment to the sample, and reversible or irreversible deformation.…”