PSI - Issue 50

5

Dmitry Parshin et al. / Procedia Structural Integrity 50 (2023) 320–326 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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a

b

Fig. 1. Contact stress distribution evolvement for the structure constructed at: (a) a very low pace; (b) a very high pace.

We set 0.3 start  t for all further examples. From the practical point of view, this means that a fairly “ young ” material capable of intense elastic and creeping deforming is supposed to be used for the construction. All figures presented show the distributions of contact stresses through the structure right bottom surface 0   , which coincide with the stresses   on this plane. We use the following symbolic representations in each figure:  the dotted line shows the stress distribution that occurred in the workpiece at the time 0 t t  of its installation on the foundation;  the solid lines show the evolvement of stress distribution over the time start t t  , when layers of new material are being added to the structure internal surface and also when the construction process has been stopped but creeping is still ongoing;  the dashed line shows the stress distribution in the finished structure when the creeping process can already be considered as finalized, that is, mathematically at  t . 4.1. Brief discussion of results for stress controlling by construction pace changing Consider the graphs plotted in Fig. 1a. They are calculated for the case of constructing the arched structure under investigation at a pace of 0.04  A . Such constructing can be considered as a very slow . Therefore, by the time the last layers of material are attached to the structure, the creeping process have almost completed in the first ones . As a result, the formers remain almost unloaded, which is shown quantitatively in Fig. 1a. Since the taken arched workpiece is thin-walled enough (its wall thickness, in accordance with (6), is 110 of the external radius), and therefore fragile, contact stress peaks occur in it at the time of installation on the foundation (dotted lines in Fig. 1), both positive (peeling the structure bottom from the foundation) and negative (pressing the structure bottom to the foundation). And we can see that it is impossible to significantly extinguish these peaks by the strengthening of this workpiece with slow adding new material to it. Let us try to increase the pace of adding material. Take 1  A which corresponds to a very fast construction. The results of made calculations for this mode are presented with graphs in Fig. 1b. In this case, as we can see, the new material layers manage to join in the creeping deformation of the entire structure and, thereby, significantly unload its workpiece part. We can also draw attention to the fact that, for the considered thin-walled structure, there is such a constructing mode between the both modes presented in Fig. 1 (with an intermediate value of the pace A ) in which the added material will almost uniformly carry contact stresses on the structure bottom at  t . If we increase the pace of constructing A to values greater than the value corresponding to Fig. 1b, then the peak of negative (pressing) contact stress in the workpiece part will be slightly more reduced, but at the same time the negative contact stress will reach a greater magnitude value near the internal surface of the structure. Thus, the mode shown in Fig. 1b can be considered close to optimal from the view point of minimizing the level of pressing contact stresses acting at  t on the bottom surface of the constructed thin-walled arched structure. 0.1 0  t and