“…In the location where the upper beam flange and the column are connected, a local weld-scale model is established by SOLID95, a type of 3D 20-node structural solid elements with mid-nodes, with a mesh size of about 5 mm at the local welding location, as shown in Figure 4(c) and (d). It has been found in the previous research (Fang et al, 2017, 2018) that the lateral weld toe and the lower weld toe (Location 1 and Location 3) are more likely to undergo stress concentration effect than the upper weld toe (Location 2), as shown in Figure 4(d), which means the corner location of the two weld toes (Location 1 and Location 3) is more susceptible to fatigue crack growth, so a sub-model with an initial three-dimensional surface edge crack at the corner between Location 1 and Location 3 is established as shown in Figure 4(e) using sub-model technology.Figure 4.Multi-scale finite element model and crack increment: (a) Multi-scale model; (b) Local connection scale; (c) Local weld-scale; (d) Location where sub-model is established; (e) Sub-model with a crack of 0.15 mm; (f) Fluctuating wind time-history; (g) Summary of crack increment.…”
Section: Case Study: Application and Improvement Of The Modelsupporting
confidence: 69%
“…Welded connections in real engineering structures differ greatly from the above standard welded joints in geometric properties, mechanical characteristics, and loading conditions. In this section, wind-induced fatigue life assessment of a welded beam-to-column connection in a steel high-rise building which has been discussed in the authors’ previous research, see Fang et al (2017, 2018), is conducted to demonstrate the application and improvement of this model to make it more applicable to real engineering structures and stochastic loading.…”
Section: Case Study: Application and Improvement Of The Modelmentioning
confidence: 99%
“…The crack increment Δainormal′ for each crack growth step is adjusted to be the average between those in the previous step and the next step, that is, Δai=(normalΔai−1′,+normalΔai′,)/2, and thus the adjusted crack increments are Δ a 1 =0.175 mm, Δ a 2 =0.425 mm, Δ a 3 =2.25 mm, Δ a 4 =4.5 mm, Δ a 5 =6.5 mm, and Δ a 6 =4 mm, so that the stress intensity factor range at the start point or the end point of each step becomes nearly at the middle point of the adjusted step to represent the stress intensity factor in the whole crack increment more precisely, as shown in Figure 4(g).(2) Suitable finite element sub-models for crack growth analysis are established and the wind loading time-histories with a duration of 50s (500 load steps) as shown in Figure 4(f) are exerted on the multi-scale FE model. The simulation of wind loading is detailed in the previous research by the authors (Fang et al, 2017, 2018). The equivalent stress intensity factor time-history at the crack tip within each adjusted crack increment i ( i = 1, 2, ..., 6, the crack growth step number), denoted as K eq i , is calculated based on equation (15) from the work of Gerstle (1986).…”
Section: Case Study: Application and Improvement Of The Modelmentioning
To investigate the fatigue crack growth of surface cracks in steel welded joints, a three-dimensional surface fatigue crack growth life assessment model considering both the surface crack growth period and the following through crack growth period is proposed. The fatigue crack growth life of a standard steel butt joint specimen is predicted considering the effect of welding residual stress and it is compared with fatigue test results. An example of a welded beam-to-column connection in a steel high-rise building under wind is selected to demonstrate the improvement of the model to make it applicable to stochastic loading and real engineering structures. The life results are compared with those obtained by other fatigue assessment approaches. The mesh sensitivity analysis is made and the effect of extreme welding imperfections and corrosion environment are both discussed. Guidance to select the fatigue life assessment approaches is also proposed. The results show that the growth shape of the edge crack remains a quarter of a circle while that of the center crack remains a quarter of an ellipse during the growth; When the surface crack grows through the plate thickness and becomes a through crack, the remaining fatigue crack growth life is unneglectable for real engineering components especially for the ones with a large plate width; The effect of welding residual stress on the fatigue crack growth life of real engineering component is complex and it depends on the distribution of the residual stress itself; The proposed three-dimensional surface crack engineering model can acquire accurate life results and is applicable to stochastic loading and engineering structures.
“…In the location where the upper beam flange and the column are connected, a local weld-scale model is established by SOLID95, a type of 3D 20-node structural solid elements with mid-nodes, with a mesh size of about 5 mm at the local welding location, as shown in Figure 4(c) and (d). It has been found in the previous research (Fang et al, 2017, 2018) that the lateral weld toe and the lower weld toe (Location 1 and Location 3) are more likely to undergo stress concentration effect than the upper weld toe (Location 2), as shown in Figure 4(d), which means the corner location of the two weld toes (Location 1 and Location 3) is more susceptible to fatigue crack growth, so a sub-model with an initial three-dimensional surface edge crack at the corner between Location 1 and Location 3 is established as shown in Figure 4(e) using sub-model technology.Figure 4.Multi-scale finite element model and crack increment: (a) Multi-scale model; (b) Local connection scale; (c) Local weld-scale; (d) Location where sub-model is established; (e) Sub-model with a crack of 0.15 mm; (f) Fluctuating wind time-history; (g) Summary of crack increment.…”
Section: Case Study: Application and Improvement Of The Modelsupporting
confidence: 69%
“…Welded connections in real engineering structures differ greatly from the above standard welded joints in geometric properties, mechanical characteristics, and loading conditions. In this section, wind-induced fatigue life assessment of a welded beam-to-column connection in a steel high-rise building which has been discussed in the authors’ previous research, see Fang et al (2017, 2018), is conducted to demonstrate the application and improvement of this model to make it more applicable to real engineering structures and stochastic loading.…”
Section: Case Study: Application and Improvement Of The Modelmentioning
confidence: 99%
“…The crack increment Δainormal′ for each crack growth step is adjusted to be the average between those in the previous step and the next step, that is, Δai=(normalΔai−1′,+normalΔai′,)/2, and thus the adjusted crack increments are Δ a 1 =0.175 mm, Δ a 2 =0.425 mm, Δ a 3 =2.25 mm, Δ a 4 =4.5 mm, Δ a 5 =6.5 mm, and Δ a 6 =4 mm, so that the stress intensity factor range at the start point or the end point of each step becomes nearly at the middle point of the adjusted step to represent the stress intensity factor in the whole crack increment more precisely, as shown in Figure 4(g).(2) Suitable finite element sub-models for crack growth analysis are established and the wind loading time-histories with a duration of 50s (500 load steps) as shown in Figure 4(f) are exerted on the multi-scale FE model. The simulation of wind loading is detailed in the previous research by the authors (Fang et al, 2017, 2018). The equivalent stress intensity factor time-history at the crack tip within each adjusted crack increment i ( i = 1, 2, ..., 6, the crack growth step number), denoted as K eq i , is calculated based on equation (15) from the work of Gerstle (1986).…”
Section: Case Study: Application and Improvement Of The Modelmentioning
To investigate the fatigue crack growth of surface cracks in steel welded joints, a three-dimensional surface fatigue crack growth life assessment model considering both the surface crack growth period and the following through crack growth period is proposed. The fatigue crack growth life of a standard steel butt joint specimen is predicted considering the effect of welding residual stress and it is compared with fatigue test results. An example of a welded beam-to-column connection in a steel high-rise building under wind is selected to demonstrate the improvement of the model to make it applicable to stochastic loading and real engineering structures. The life results are compared with those obtained by other fatigue assessment approaches. The mesh sensitivity analysis is made and the effect of extreme welding imperfections and corrosion environment are both discussed. Guidance to select the fatigue life assessment approaches is also proposed. The results show that the growth shape of the edge crack remains a quarter of a circle while that of the center crack remains a quarter of an ellipse during the growth; When the surface crack grows through the plate thickness and becomes a through crack, the remaining fatigue crack growth life is unneglectable for real engineering components especially for the ones with a large plate width; The effect of welding residual stress on the fatigue crack growth life of real engineering component is complex and it depends on the distribution of the residual stress itself; The proposed three-dimensional surface crack engineering model can acquire accurate life results and is applicable to stochastic loading and engineering structures.
“…However, if large-scale complicated engineering structures are involved, the case is a little different. Unlike small specimens involved in fatigue tests, the failure consequence of engineering structures is extremely serious and may give rise to much loss of life and property; so in the engineering field, it is more reasonable in practice to obtain a more conservative fatigue assessment result than a relatively dangerous result, see the work by Fang et al (2018). Besides, it is sometimes recommended to reach a higher margin of safety and to adopt a certain value of safety factors to take into account other uncertainties like the complicated environment which may bring about the problem of erosion fatigue and the effect of residual stress after welding.…”
Axial low-cycle fatigue tests are conducted on transverse butt joint specimens and cruciform joint specimens made of carbon structural steel GB Q235B. The effect of slip between the specimens and the grips of the test machine is considered by the proposal of a linear slip model. The cyclic softening properties are studied by observing the variation of stress amplitude with cycles. The cyclic stress-strain curve and the strain-life curve for both kinds of specimens are obtained based on the fatigue test data, and the corresponding coefficients are fitted. In order to verify the fatigue test results, finite element models of specimens are established and the corresponding fatigue life assessment is conducted using the local stress-strain approach and the equivalent structural stress approach, respectively. The results show that the effect of slip is unneglectable and the established linear slip model is reasonable. The two kinds of specimens both show a strain softening property, but cruciform joint specimens experience sudden falls of stress amplitude during the test due to the damage of welded lines; cruciform joint specimens show an either one-side failure mode or two-side failure mode while butt joint specimens only show a one-side failure mode; the two-side failure mode tends to lead to shorter fatigue life, so in the design of cruciform joint, such failure mode should be avoided.
“…Then, in welded joints applications, the use of TCD allows to FE model a null notch radius without affecting the results as long as the radius real value is smaller than L. More recently, Fang et al 44 addressed the problem of stress concentration in wind-induced fatigue assessment of welded structures by adopting TCD. This study confirmed TCD reliability in this field of application.…”
Theory of Critical Distances (TCD) collects several methods adopted in failure prediction of components provided with stress concentration features. The idea of evaluating stress effect in a zone rather than in a single point was proposed decades ago but, only thanks to relatively recent works, TCD concepts showed to be a successful extension of Linear Elastic Fracture Mechanics (LEFM), able to assess strength and fatigue life. The increasing computational power has made Finite Element Method (FEM) widespread, hence stress fields can be easily extracted and used as input data for fatigue post-processing and durability analyses. In this scenario, TCD reveals as a powerful tool which, thanks to the introduction of a single material parameter (critical distance, [Formula: see text]), integrates classical fracture models by considering the presence of microscale phenomena acting in fracture process. In this sense, TCD behaves as a link between continuum mechanics and LEFM. Modalities and reasons for this connection to occur are interesting points of further investigations. Literature on TCD and its theoretical-experimental background is quite extended, nevertheless few industrial applications are available in literature to the best of authors’ knowledge. In this paper, an overview of concepts and applications related to TCD are reported highlighting the relevance of theoretical arguments in actual applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
