Fractography

About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.

Interlayer fracture toughness of additively manufactured unreinforced and carbon-fiber-reinforced acrylonitrile butadiene styrene

Abstract: This study presents development of a test method for characterization of interlayer, mode-I fracture toughness of fused filament fabrication (FFF) materials using a modified double cantilever beam (DCB) test. This test consists of DCB specimen fabricated from using unidirectional FFF layers, an 8 μm Kapton starter crack inserted in the midplane during the printing process, and reinforcing glass/epoxy doublers to prevent DCB arm failure during loading. DCB specimens are manufactured with a commercially available 3D printer using unreinforced Acrylonitrile Butadiene Styrene (ABS) and chopped carbon-fiber-reinforced ABS (CF-ABS) filaments. To examine the effect of the FFF printing process on fracture toughness, additional ABS and CF-ABS specimens are hot-press molded using the filament material, and tested with the single end notch bend (SENB) specimen configuration. The fracture toughness data from DCB and SENB tests reveal that the FFF process significantly lowers the mode-I fracture toughness of ABS and CF-ABS. For both materials, in situ thermal imaging and post-mortem fractography shows, respectively, rapid cool-down of the rasters during filament deposition and presence of voids between adjacent raster roads; both of which serve to reduce fracture toughness. For CF-ABS specimens, fracture toughness is further reduced by inclusion of poorly wetted chopped carbon fibers. Although this study did not attempt to optimize the fracture performance of FFF specimens, the results demonstrate that the proposed methodology is suitable for design and optimization of FFF processes for improved interlayer fracture performance.

Microstructure and Mechanical Properties of Ti-6Al-4V Manufactured by SLM

Abstract: The article presents results of a study of phase composition and microstructure of initial material and samples obtained by selective laser melting of titanium-based alloy, as well as samples after heat treatment. The effect of heat treatment on microstructure and mechanical properties of specimens was shown. It was studied mechanical behavior of manufactured specimens before and after heat treatment at room and elevated temperatures as well. The heat treatment allows obtaining sufficient mechanical properties of material at room and elevated temperatures such as increase in ductility of material. The fractography of samples showed that they feature ductile fracture with brittle elements.

The significance of fractography for investigations of fatigue crack growth under variable-amplitude loading

Abstract: Fatigue crack growth tests were carried out on 2024-T3 and 7075-T6 centrally cracked specimens. Variable-amplitude (VA) load spectra were used with periodic overload (OL) cycles added to constant-amplitude (CA) cycles. The fatigue fracture surfaces were examined in the SEM to obtain more detailed information on crack growth contributions of different load cycles. The striation patterns could be related to the load histories. SEM observations were related with (i) delayed retardation, (ii) the effect of 10 or a single OL on retardation, (iii) crack growth during the ()L cycles, and (iv) crack growth arrest after a high peak load. Fractographs exhibited local scatter of crack growth rates and sometimes a rather tortuous 3D geometry of the crack front. Indications of structurally sensitive crack growth under VA loading were obtained. Fractography appears to be indispensable for the evaluation of fatigue crack growth prediction models in view of similarities and dissimilarities between crack growth under VA and CA loading.

In situ fracture observation and fracture toughness analysis of squeeze cast AZ51–xSn magnesium alloys

Abstract: Effects of Sn addition on microstructural modification and microfracture mechanisms of squeeze cast AZ51– x Sn magnesium alloys were investigated by in situ fracture and fractographic observations. Microstructural analyses indicated that Mg 2 Sn particles as well as Mg 17 Al 12 particles were precipitated mainly along solidification cell boundaries, and the volume fraction of Mg 2 Sn particles increased with increasing Sn addition, thereby leading to the increase in strength. According to observation of microfracture processes of the AZ51–7Sn alloy, the fracture proceeded mainly along cell boundaries as the crack initiated at the notch tip propagated mainly along intercellular Mg 17 Al 12 and Mg 2 Sn particles. In the AZ51 and AZ51–3Sn alloys, on the other hand, the deformation and fracture proceeded into cells rather than into cell boundaries as twins were actively developed inside cells, although some microcracks were initiated at Mg 17 Al 12 or Mg 2 Sn particles. This resulted in the improved fracture properties, which was also confirmed by the R -curve analysis. These findings suggested that the addition of 3–5 wt.% Sn was effective in improving both tensile and fracture properties, which was explained by mechanisms such as development of twins in the Mg matrix, blocking of crack growth, and crack blunting.