Study of the resistance to crack propagation in alumina by acoustic emission

Indentation testing and its acoustic emission response: applications and emerging trends

“…Table 2 summarises the key information related to the published work on AE monitoring of indentation in bulk ceramic materials. It indicates that the material accommodation mechanisms are material and microstructure dependent; however, they are almost dominated by the ‘burst type high amplitude AE signals’ due to cracking98,99 – 115 with some evidence of AE associated with plasticity97,105,109,114,116 – 118 and phase transformation 111. Localised microstructural variations such as defects and local porosity have also been found to dictate the AE during the indentation process 102.…”

“…Each mechanism type has been studied from the point of view of monitoring and interpreting the surface as well as the bulk response of materials using raw AE signals and its associated features. 98,[99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115] with some evidence of AE associated with plasticity 97,105,109,114,[116][117][118] and phase transformation. 111 Localised microstructural variations such as defects and local porosity have also been found to dictate the AE during the indentation process.…”

“…15 AE monitored Hertzian indentations of alumina ceramic where AE bursts correspond to indenter loading attributed to material cracking99 16 AE monitored spherical shaped indentations of crystals a in silicon showing transformation thrust in unloading curve with no AE activity in that zone and b in sapphire with no thrust in unloading curve110 17 AE monitored Hertzian indentation of ceria stabilised tetragonal zirconia polycrystal (Ce-ZP) at constant crosshead speed of 1?0 mms 21 and 3000 N peak load: a indentation surface of Ce-ZP-III (grain size: 2?2 mm) showing uplift outside impression edge which corresponds to t-m transformation ring; and b cumulative acoustic amplitude versus contact time during indentation load/unload in Ce-TZP-I (grain size: 1?1 mm), Ce-TZP-II (grain size: 1?6 mm), Ce-TZP-III (grain size: 2?2 mm) and Ce-TZP-IV (grain size: 3?0 mm) specimens, indicating acoustic activity increases with increasing grain size 111Faisal et al Indentation testing and its acoustic emission response International Materials Reviews 2011 VOL 56 NO 2 strain) may not produce any AE. Ray et al 106 also noted that the number of AE hits increased with increasing indentation load leading to microscopically observed intergranular fracture and Palmqvist type cracks although they did not directly correlate AE with radial surface crack opening.…”

Improvement in Contact Strength of Si3N4/SiC Composite by Crack Healing

“…The ring crack initiation load was determined using AE. Bouras et al [10] stated that subcritical crack growth is one of the sources of AE in ceramic materials. The loading was interrupted at the load detected by AE.…”

Identification of the fragmentation of brittle particles during compaction process by the acoustic emission technique

“…The AE technique is generally used to monitor real-time processes that emit acoustic waves. It is also used to detect and/or monitor defaults and cracks in materials [17][18][19], and to monitor the compaction of metallic [20,21], pharmaceutical [22,23] or ceramic [24] powders. Indeed, the final step of the process (i.e.…”