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Predictive Approach to Creep Life of Ni-based Single Crystal Superalloy Using Optimized Machine Learning Regression Algorithms
Published in Amar Patnaik, Vikas Kukshal, Pankaj Agarwal, Ankush Sharma, Mahavir Choudhary, Soft Computing in Materials Development and its Sustainability in the Manufacturing Sector, 2023
Vinay Polimetla, Srinu Gangolu
The microstructural evolution of matrix and precipitated phases (γ/γʹ phases) results in three different regimes of creep that would occur in Ni-SXs generally. The creep mechanisms involved within these regimes inherently correlate with the interactions between the dislocations and their movement inside the material. In principle, the dislocation-free zone of γ matrix experiences the multiplication of dislocations initially with respect to external temperature and stress. A short ordered interval exists where dislocations try to homogenize within those strained matrix channels and plasticity follows along the γ/γʹ interfacial vicinity. As the shift of mechanical properties takes place from elastic to plastic behavior, the primary creep can be identified by the onset of plastic flow.
Viscoelastic Behaviour
Published in B. R. Gupta, Rheology Applied in Polymer Processing, 2023
The viscoelastic materials when subjected to a constant stress experience a time-dependent increase in strain. This phenomenon is known as viscoelastic creep. It is also referred as cold flow. It is defined as the tendency of the solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long term exposure to high stresses, which are below the yield strength of the material. Creep is more severe in materials that are subjected to thermal stresses for long periods, and generally increases as the material nears its melting point.
The Oslofjord subsea tunnel, a case record
Published in Jean-François Thimus, Ground Freezing 2000 - Frost Action in Soils, 2020
Classical creep theory defines 3 deformation phases: primary creep, secondary creep and tertiary creep, (se Fig. 5) where the strain velocity is decreasing, constant and increasing respectively. Creep failure is traditionally defined as a rupture, or instability leading to a rupture. Creep strength is defined as the stress level at which after a finite time interval, failure occurs. In practice, strength or failure is usually taken as the transition between secondary and tertiary creep phase. But several authors found that it is difficult to predict how long the secondary creep phase will last, and it is thus a question of time as to when the rupture will occur. As a result of this, the definition of creep strength in the Berggren creep model is defined as the transition between primary and secondary creep.
Reliability based failure assessment of deteriorated cast iron pipes lined with polymeric liners
Published in Structure and Infrastructure Engineering, 2023
Guoyang Fu, Benjamin Shannon, Rukshan Azoor, Jian Ji, Ravin Deo, Jayantha Kodikara
It is widely recognized that plastics are susceptible to creep and CIPP and polymeric spray liners are no exception. Creep is defined as the continuing deformation with time when the material is subjected to a constant load. Creep can occur because of long-term exposure to stresses that are still below the yield stress of the material. A creep retention factor (CRF) is commonly utilised to consider the creep modulus of CIPP and spray liners and it is defined as the ratio of the creep modulus to the initial modulus of elasticity (ASTM D2990-01, 2001; Knight & Bontus, 2018). The creep modulus () can be found by multiplying the corresponding creep retention factor by the initial modulus of elasticity : where, is the creep retention factor (dimensionless). The following equation can be used to determine the CRF and subsequently the creep modulus at any point in time (Shannon et al., 2021): where, and are coefficients, which can be determined by fitting results of standard creep tests (ASTM D2990-01, 2001) to Equation (3).
Recoverability effects on reliability assessment for accelerated degradation testing
Published in IISE Transactions, 2023
Chengjie Wang, Jian Liu, Qingyu Yang, Qingpei Hu, Dan Yu
This research focuses on partial recovery, as it can be observed in various typical failure modes that have not yet been adequately studied. For example, elastic, plastic, and creep deformation are three major types of deformation in creep strain. Elastic strain will have a full recovery instantly if the stress is released, and some of the creep strain may be partially recovered after a period of time (Dowling, 2012). The failure mode of Negative Bias Temperature Instability (NBTI) has been commonly observed in semiconductor products, and it is an important factor affecting the reliability of p-MOSFETs below 100 nm (Wittmann et al., 2005). Open circuit voltage recovery has been observed in fuel cells with temperature excursions (Kundu et al., 2008). Partial recovery has also been observed in the degradation process of lithium-ion batteries (Tang et al., 2014; Zhang et al., 2017). Although the recoverability phenomenon has been observed, traditional modeling methods without explicit consideration of recovery were used to fit these types of data, leading to overestimation in lifetime inference (Kapre et al., 2007).
Experimental evaluation of uniaxial strength and creep behavior of frozen gravel
Published in Journal of the Chinese Institute of Engineers, 2022
Yaqin Zhang, Ping Yang, Lin Li
The uniaxial creep test results for frozen gravel are presented in Figure 5. Under stress levels of 0.93 MPa and 1.86 MPa, the specimens undergo a decaying creep. This type usually occurs when the stress applied to the specimen is less than the corresponding long-term strength (i.e. corresponding stress at failure when time tends to infinity). The creep increasing rate gradually decreases and the creep strain eventually reaches a constant value. At stress of 2.33 MPa and 2.80 MPa, instead of reaching a constant value at the end, the soil creep strain rate quickly increased with increasing time. This type of creep usually occurs when the stress applied exceeds the corresponding soil long-term strength. This type of creep deformation mainly consists of three stages: the primary creep (І) is the decaying stage with a decreasing creep rate; the secondary creep (II) is a steady stage with a constant creep rate; and the tertiary creep (III) is an accelerating stage with a continuously increasing creep rate that eventually leads to failure.