scholarly journals Performance-Related Characterization of Forming-Induced Initial Damage in 16MnCrS5 Steel under a Torsional Forward-Reverse Loading Path at LCF Regime

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2463
Author(s):  
Kerstin Moehring ◽  
Frank Walther
Keyword(s):  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Fatigue Performance ◽  
Loading Path ◽  
Load Path ◽  
Operation Conditions ◽  
Initial Damage ◽  
Torsional Testing ◽  
Local Material Properties

Forming technology and in particular cold forward rod extrusion is one of the key manufacturing technologies with regard to the production of shafts. The selection of process parameters determines the global and local material properties. This particularly implies forming-induced initial damage in representation of pores. On this background, this study aims on describing the influence of these pores in the performance of the material 16MnCrS5 (DIN 1.7139, AISI/SAE 5115) under a torsional load path in the low cycle fatigue regime, which is highly relevant for shafts under operation conditions. For this purpose, the method of cyclic forward-reverse torsional testing was applied. Additionally, intermittent testing method and the characterization of the state of crack growth using selective electron microscopy analysis of the surface were combined. A first attempt was made to describe the influence of forming-induced initial damage on the fatigue performance and the crack growth mechanisms. The correlation of fatigue performance and initial damage was contiguous in the sense that the initial damage corresponds with a decrease of material performance. It was concluded that the focus of further investigations must be on small crack growth and the related material changes to identify the role of initial damage under cyclic loads.

Characterization of Crack Growth in BGA Under Drop Impact

2013 ◽  
Author(s):  
Quang Nguyen ◽  
Seungbae Park ◽  
Tung Nguyen
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Solder Joints ◽  
Low Cycle Fatigue ◽  
Drop Impact ◽  
Drop Tests ◽  
Microscope Imaging ◽  
Cyclic Approach

This paper presents the characterization of the crack growth rate of Sn-4.0wt.%Ag-0.5wt.%Cu (SAC405) solder joints under drop impact. Several actual ChipArray® BGA (CTBGA) packages were cross-sectioned, polished and used as the test vehicles. The ball drop tests were performed using a specially-designed tester. The drop impact from the drop ball induces bending in the PCB, which damages the solder joints. The crack lengths in the solder joints were measured after every five drops using microscope imaging. Crack growth rates were calculated from the test results. Insight into the crack growth rate in solder joints under drop impact is provided. The direct cyclic approach for low-cycle fatigue analysis in ABAQUS was used to simulate the crack growth in the solder joints.

Low-Cycle Fatigue Performance of Buckling Restrained Braces and Assessment of Cumulative Damage under Severe Earthquakes

2018 ◽  
Vol 763 ◽  
pp. 867-874
Author(s):  
Yu Shu Liu ◽  
Ke Peng Chen ◽  
Guo Qiang Li ◽  
Fei Fei Sun
Keyword(s):  
Fatigue Life ◽  
Energy Dissipation ◽  
Structural Reliability ◽  
Low Cycle Fatigue ◽  
Engineering Application ◽  
Fatigue Performance ◽  
Cycle Fatigue ◽  
Variable Amplitude ◽  
Buckling Restrained Braces ◽  
Energy Dissipation Devices

Buckling Restrained Braces (BRBs) are effective energy dissipation devices. The key advantages of BRB are its comparable tensile and compressive behavior and stable energy dissipation capacity. In this paper, low-cycle fatigue performance of domestic BRBs is obtained based on collected experimental data under constant and variable amplitude loadings. The results show that the relationship between fatigue life and strain amplitude satisfies the Mason-Coffin equation. By adopting theory of structural reliability, this paper presents several allowable fatigue life curves with different confidential levels. Besides, Palmgren-Miner method was used for calculating BRB cumulative damages. An allowable damage factor with 95% confidential level is put forward for assessing damage under variable amplitude fatigue. In addition, this paper presents an empirical criterion with rain flow algorithm, which may be used to predict the fracture of BRBs under severe earthquakes and provide theory and method for their engineering application. Finally, the conclusions of the paper were vilified through precise yet conservative prediction of the fatigue failure of BRB.

A macroscopic theory of microcrack growth in brittle materials

1991 ◽  
Vol 335 (1639) ◽  
pp. 455-485 ◽  
Keyword(s):  
Crack Growth ◽  
Brittle Materials ◽  
Macroscopic Theory ◽  
Rate Of Increase ◽  
Inelastic Behaviour ◽  
Constitutive Response ◽  
Macroscopic Plasticity ◽  
Microcrack Growth ◽  
Vector Valued

This paper is concerned with the development of a macroscopic theory of crack growth in fairly brittle materials. Average characteristics of the cracks are described in terms of an additional vector-valued variable in the macroscopic theory, which is determined by an additional momentum-like balance law associated with the rate of increase of the area of the cracks and includes the effects of forces maintaining the crack growth and the inertia of microscopic particles surrounding the cracks. The basic developments represent an idealized characterization of inelastic behaviour in the presence of crack growth, which accounts for energy dissipation without explicit use of macroscopic plasticity effects. A physically plausible constraint on the rate of crack growth is adopted to simplify the theory. To ensure that the results of the theory are physically reasonable, the constitutive response of the dependent variables are significantly restricted by consideration both of the energetic effects and of the microscopic processes that give rise to crack growth. These constitutive developments are in conformity with many of the standard results and observations reported in the literature on fracture mechanics. The predictive nature of the theory is illustrated with reference to two simple examples concerning uniform extensive and compressive straining.

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