Investigation of constraint and warm prestressing effects by means of a local approach to fracture

2015 ◽  
Vol 136 ◽  
pp. 26-37 ◽  
Author(s):  
Guian Qian ◽  
Markus Niffenegger
Author(s):  
Jiri Novak

Effect of WPS in ferritic alloys 15Kh2MFA (CrMoV) and 18MND5 increases with prestress level more rapidly than Chell’s model predicts; this observation had not been understood until now. In this work, experimental data are presented concerning behaviour of steels under simple Load – Unload – Cool – Fracture history. Chell’s model uses as input quantity true fracture toughness and predicts, for simple temperature and loading histories, apparent fracture toughness. A new proposed model based on local approach corrects value of true fracture toughness as an input quantity for Chell’s formulas. Idea of the true fracture toughness increase consists in deactivation of fracture initiation particles during preload. But another interpretation is also possible: Retarding influence of dislocation substructure formed during preload (phase L) on the cleavage microcrack growth at low temperature during loading to fracture (phase F) may cause similar effect. Universal behaviour found in both steels indicates that the second interpretation is more realistic one.


2015 ◽  
Vol 750 ◽  
pp. 104-113
Author(s):  
Gui An Qian ◽  
Markus Niffenegger

One potential challenge to the integrity of the reactor pressure vessel (RPV) in a pressurized water reactor is posed by pressurized thermal shock (PTS). Therefore, the safety of the RPV with regard to neutron embrittlement has to be analyzed. In this paper, the procedure and method for the structural integrity analysis of RPV subjected to PTS is presented. The FAVOR code is applied to calculate the probabilities for crack initiation and failure by considering crack distributions based on cracks observed in the Shoreham and PVRUF RPVs in the U.S. A local approach to fracture, i.e. the σ*-A* model is used to predict the warm prestressing (WPS) effect on the RPV integrity. The results show that the remaining stress contributes to the WPS effect, whereas the increase of fracture toughness is not completely attributed to the remaining stress. The modeled load paths predict a material toughness increase of 30-100%.


2005 ◽  
Vol 28 (6) ◽  
pp. 1112-1122 ◽  
Author(s):  
Ji Li ◽  
C. W. Chan ◽  
Hong-Yue Zhang

1994 ◽  
Vol 116 (3) ◽  
pp. 267-273 ◽  
Author(s):  
H. Okamura ◽  
G. Yagawa ◽  
T. Hidaka ◽  
Y. Urabe ◽  
M. Satoh ◽  
...  

Fracture tests for the verification of WPS (warm prestressing) effect were carried out by using large flat specimens and big compact specimens with low toughness. In the case of monotonical KI increasing during cooling, the specimen broke within the scatter band of KIC. On the other hand, when KI was decreasing during cooling, the specimens did not break even if KI values were beyond the scatter band of KIC. That is, WPS effect was confirmed even for the low toughness steel like reactor pressure vessel wall under neutron irradiation. Also, KI values at fracture can be predicted by Chell’s theory. By applying WPS effect and the predictive equations for irradiation embrittlement for Japanese PWR reactor steels to the PTS integrity analysis, much more temperature margin can be expected.


Proceedings ◽  
2021 ◽  
Vol 77 (1) ◽  
pp. 12
Author(s):  
Annemarie van de Weert

In recent years, the fight against terrorism and political violence has focused more on anticipating the threats that they pose. Therefore, early detection of ideas by local professionals has become an important part of the preventive approach in countering radicalization. Frontline workers who operate in the arteries of society are encouraged to identify processes towards violent behavior at an early stage. To date, however, little is known about how these professionals take on this screening task at their own discretion. Research from the Netherlands suggests that subjective assessment appears to exist. This is due to the absence of a clear norm for preliminary judgments. However, such an approach affects prejudice or administrative arbitrariness, which may cause side effects due to unjustified profiling. The publications about the Dutch case are inspired by the concept of “performativity”, (de Graaf, B., & de Graaff, B. G. J. (2010). Bringing politics back in: The introduction of the ‘performative power’ of counterterrorism. Critical Studies on Terrorism, 3(2), pp. 261–275.) which points to a distinct relationship between the performative power of counterterrorism instruments and the effectiveness of the local approach. Performativity contends that the overall effect of the policy in question is not necessarily determined by the policy measures and their intended results, as such, but more by the way in which they are presented and perceived. This means that, in order to create an equitable approach, governments, whether local or national, should focus more on the actual practice performed by frontline practitioners. The focus on practices is part of a larger project, entitled ‘Gatekeepers of Justice’ (See: https://www.internationalhu.com/research/access-to-justice), by the Research Group Access2Justice (Research Centre of Social Innovation at Utrecht University of Applied Science), led by professor Quirine Eijkman, Deputy President of the Netherlands Institute for Human Rights.


2014 ◽  
Vol 5 (4) ◽  
pp. 262-278
Author(s):  
A. Sellitto ◽  
R. Borrelli ◽  
F. Caputo ◽  
A. Riccio ◽  
F. Scaramuzzino

Purpose – The purpose of this paper is to investigate on the behaviour of a delaminated stiffened panel; the delamination growth is simulated via fracture elements implemented in B2000++® code based on the Modified Virtual Crack Closure Technique (MVCCT), matrix cracking and fibre failure have been also taken into account. Design/methodology/approach – In order to correctly apply the MVCCT on the delamination front a very fine three-dimensional (3D) mesh is required very close to the delaminated area, while a 2D-shell model has been employed for the areas of minor interest. In order to couple the shell domain to the solid one, shell-to-solid coupling elements based on kinematic constraints have been used. Findings – Results obtained with the global/local approach are in good correlation with those obtained with experimental results. Originality/value – The global/local approach based on kinematic coupling elements in conjunction with fracture elements allows to investigate and predict the behaviour of a stiffened delaminated composite panel in an efficient and effective way.


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