Abstract:From a common viewpoint, fatigue fracture of materials is simulated by the process of initiation of an initial macrocrack of length a i = d* (d* is the constant of the material), which is successively (stepwise) repeated at the stage of its growth. As a result, the diagram "range of local stresses -period of initiation of an initial macrocrack" or "range of local strains -period of initiation of an initial macrocrack," which was determined for notched specimens, can be used for the construction of the diagram … Show more
In low-cycle fatigue process, plastic strain takes place at notch root vicinity fast appears induced by high stress concentration. Plastic strain makes material non-uniform and the change of distribution of local stress. The approximation to stress concentration point of Neuber’s rule is not suitable for some plastic materials in engineering practice. In this paper, the average strain of fatigue process zone was considered to substitute Neuber strain for predicting fatigue life. Prediction results indicated that average strain range of fatigue process zone is more suitable than Neuber strain range for predicting low-cycle fatigue life of LY12CZ.
In low-cycle fatigue process, plastic strain takes place at notch root vicinity fast appears induced by high stress concentration. Plastic strain makes material non-uniform and the change of distribution of local stress. The approximation to stress concentration point of Neuber’s rule is not suitable for some plastic materials in engineering practice. In this paper, the average strain of fatigue process zone was considered to substitute Neuber strain for predicting fatigue life. Prediction results indicated that average strain range of fatigue process zone is more suitable than Neuber strain range for predicting low-cycle fatigue life of LY12CZ.
“…The second stage is characterized by the crack propagation up to a com plete body failure. N owadays, there are attem pts to describe the entire process o f fatigue fracture from a single perspective, w ith the leading role given to the process zones w hich are form ed both during the first (incubation) period and at the crack grow th stage [1][2][3][4][5][6]. The grow ing fatigue crack is regarded as a sharp notch and its grow th is m odeled as repeated crack initiation events w hich follow the sam e law s as those governing the initiation o f the prim ary crack.…”
A model o f the formation and evolution o f a local plastic deformation zone at the crack tip is proposed based on the analysis o f the main physical processes taking place in a metallic material under the action o f cyclic loads. An equation o f fatigue crack growth rate curves, which explicitly accounts fo r the loading frequency, was derived. The equation applies to the whole range o f crack lengths from short cracks to macroscopic ones. K e y w o r d s : local plastic deform ation, surface energy, fatigue strength, fatiguecrack grow th resistance, loading frequency.In tro d u c tio n . Fracture o f a m aterial and structural elem ent under external therm om echanical loading is a tw o-stage process. The first stage involves damage accum ulation in the m aterial and com es to an end w hen the param eters o f the local plastic deform ation zone reach their critical values, w hich corresponds to the beginning o f the form ation o f one or several cracks. The second stage is characterized by the crack propagation up to a com plete body failure. N owadays, there are attem pts to describe the entire process o f fatigue fracture from a single perspective, w ith the leading role given to the process zones w hich are form ed both during the first (incubation) period and at the crack grow th stage [1][2][3][4][5][6]. The grow ing fatigue crack is regarded as a sharp notch and its grow th is m odeled as repeated crack initiation events w hich follow the sam e law s as those governing the initiation o f the prim ary crack.The m ajor characteristics o f the loading conditions include the frequency of the acting load. The few m odels considering the frequency either contain it in an im plicit form [7], or cover only one or several m aterials [8][9][10], or are difficult to apply in practice [11].B ased on the above, w hat seems topical to us is the creation o f unified m odels covering the w idest possible range o f factors that influence the fatigue fracture process, relying on the analysis o f physical processes that take place in a m etallic m aterial, and having a sufficiently simple, easy-to-use m athem atical form.P h y sic a l F o u n d a tio n s o f th e F r a c tu r e M odel. E arlier w e analyzed experim ental data, both our ow n and those from literature, on the processes o f fatigue dam age accum ulation and fatigue crack propagation in m etallic m aterials using such techniques as optical, transm ission electron, and scanning electron m icroscopies com bined w ith a quantitative data processing and the determ ination o f the residual electrical resistivity and internal friction. This m ade it possible to establish basic general laws for the evolution o f the m aterial structure and variation o f the fractographic characteristics under cyclic loading. D etailed results o f these investigations are given in [12]. H ere w e outline only the key issues.
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