Application Of Fractography Research Articles

Application of Fractography and Finite Element Analysis Adopting Elastic Foundation Stiffness to Improve Fatigue Life of Main Shaft in Mechanical Press

The main shaft of a mechanical press inevitably includes significant stress concentrations that can trigger severe mechanical damage and finally lead to failure under repetitive use. In this study, an efficient procedure to quantitatively evaluate the fatigue life of the shaft system including the main shaft and its support bearings, based on the macroscopic failure analysis of the main shaft broken during actual use, was investigated. For this purpose, the bearing support was modeled as an elastic foundation, and the elastic foundation stiffness value was varied to determine the optimal value that best simulates the failure behavior, especially with respect to the failure location and failure sequence, of an actual shaft. While the finite element mesh size was kept the same, only the effect of elastic foundation stiffness was investigated. The optimum value for the main shaft investigated in this study was approximately 60 N/mm³, and the fatigue life of the shaft was evaluated based on the conventional maximum principal stress theory. Based on this, two modified designs to enhance the fatigue life of the existing shaft are proposed.

Investigating reverse butterfly fractures: An experimental approach and application of fractography

Butterfly fractures are expected to form with the transverse portion on the tension side and the wedge portion on the compression side of a bent bone, however wedges have also been observed in the reverse orientation and are reported to be frequent in concentrated 4-point bending. To investigate how these fractures form, concentrated 4-point bending experiments were performed on nine human femora and documented using high-speed video. Videos showed the wedge portion formed as fracture initiated in tension, branched obliquely, then curved to terminate on the tension face. The transverse portion formed as a crack traveled between the curved fracture branch and the compression face. Fractography was also applied to evaluate fracture surfaces. At least one fractography feature was present in all femora and 32/35 bone fragments examined. Fracture propagation sequences interpreted using fractography matched those observed on video, demonstrating the utility of this method for evaluating complex fracture patterns.

Fractographic approach to metallurgical coke failure analysis. Part 1: Cokes of single coal origin

Metallurgical coke is a complex brittle heterogeneous material consisting of carbon derived from fusible, semi-fusible and inert coal particles that forms a porous composite matrix. This paper presents a novel approach to assess and quantify the breakage behaviour and microstructural weaknesses in a pilot oven metallurgical coke. The approach uses fractography, a method commonly applied to determine the fracture behaviour and origin(s) in homogeneous materials, such as metals and ceramics. Determination of the fracture origin(s), paths of crack propagation and microstructural weaknesses in such a complex heterogeneous material as metallurgical coke represents a significant advance in both the application of fractography and the assessment of coke strength and breakage behaviour. Identification of the key features that contribute to the coke’s failure will facilitate better prediction of coke strength from coal properties and ultimately optimisation of the coal blending process.Key features and markings have been clearly identified on fracture surfaces that can either be traced back to the fracture origin or give an indication of the type of fracture or stresses to which the coke has been subjected, including the directionality and strength of those stresses. These markings include hackle, hackle twist and wallner lines, as well as markings generated by conchoidal and overload fractures.A three-step approach was applied to determine the breakage behaviour in stabilized lumps of the pilot oven coke, in which fractured coke surfaces were analysed at the macro, micro and submicron levels. The observed mechanisms of failure were quantified and summarised using a radar diagram.

S0403-1-3 多孔質アルミナの強度評価における破面観察の適用([S0403-1]セラミックスおよびセラミックス系複合材(1))

S0403-1-3 多孔質アルミナの強度評価における破面観察の適用([S0403-1]セラミックスおよびセラミックス系複合材(1))

The application of fractography to demonstrate the presence of crack tip residual stresses during programmed fatigue crack propagation in mild steel

Constant amplitude and programmed loading fatigue crack propagation tests were carried out on a low carbon steel in three point bending. The Palmgren-Miner summation(Σ N n ) was found to be consistent and always slightly greater than unity irrespective of the load program. It is suggested that this effect is caused by crack tip compressive stresses opposing propagation. Fracture surface observations using a scanning electron microscope showed changes in fracture mode immediately after a load drop from which it was possible to make estimates of the levels of residual stress present.