Satoru Izawa

Plastic Collapse Evaluation on the Notched Stainless Steel Piping Subjected to Combined Tension and Bending by Photo-Elastic Coating

This study is concerned with the structural integrity evaluation of stainless steel piping with a notch. Structural engineers seek to prevent such problems by guaranteeing a sufficient margin for the fracture strength based on the existence of assumed defects. In this study, both the tension force due to internal pressure and the bending moment caused by earthquakes are considered as a given load for a structure. Collapse load is now evaluated when a plant is under complex load condition. The stress state of a plastic collapse point is assessed using a chart of membrane stress and axial displacement as well as a chart of bending stress and deflection angle. The collapse point adopted here for evaluation method is two-times displacement method for the reason of determining the collapse point on the chart comparatively clearly. On the other hand, by observing the ligament portion of a specimen is observed using the photo elastic coating and the collapse point is determined by comparing it to a penetration point in the plastic region in the ligament. It has been found that a different load pattern affects the formation of the plastic region and also the position of the plastic collapse point. As a result, a new method for the assessment of the plastic collapse under complex load has been successfully developed. Introduction Single-edge cracked member subjected to combined tension and bending is a representative model in carrying out the structural integrity evaluation. The research has been carried out until now on this model from various fields of ductile fracture and plastic collapse[1]-[6]. The crack seems to finally come to the plastic collapse with the decrease in the ligament area, if crack extension does not become unstable under progress, when structural member with the crack does ductile fracture. It is important to clarify the load history dependency on the plastic collapse load of single-edge cracked member subjected to combined tension and bending in order to improve the accuracy of structural integrity evaluation. Authors developed statically indeterminate fracture mechanics experimental equipment which enabled us to examine the load history dependency on plastic collapse load of the member[7]. We visualized the plastic region by the photo elastic coating method to observe the formation process of the plastic region of the ligament, using a photo elasticity film made of cold setting epoxy resin. Experimental method Experimental equipment has been specially developed to cope with the indeterminate problems in fracture mechanics. It is possible that the equipment take axial force and bending at the simultaneous load or optical order. The experiment is carried out in the three test cases shown, (1) Axial force and bending simultaneous load test = Pattern (Tension + Bending). (2) Tension-after-bending test = Pattern (Bending → Tension). (3) Bending-after-tension test = Pattern (Tension → Bending). Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 2001-2005 doi:10.4028/www.scientific.net/KEM.270-273.2001

Flow Stress in a Notched Austenitic Stainless Steel Specimen Under Combined Tension and Bending

A load history-dependence of tension and bending does not exist in the brittle fracture where linear elastic fracture mechanics is applicable. However, load history-dependency does exist in a plastic collapse load of a member. The load history-dependency of plastic collapse load of a single-edge cracked member subjected to combined tension and bending for accurate structural integrity evaluation was studied in this paper. For this purpose, the authors developed a statically indeterminate fracture mechanics failure testing system, which examines of the load history-dependency of the plastic collapse of the member, by applying an axial force and a bending moment. The plastic constraint factor, the plastic collapse load and the 0.2% proof strength all exceeded the upper bound solution. Therefore, the flow stress is used in place of the plastic collapse load as an effective stress. In general, the flow stress is typically used at the average of the proof stress and the tensile strength. This paper describes the experimental result of the load history-dependency of the flow stress in a single-edge notched specimen test. The experimental result showed the load history-dependency on the flow stress in single-edge notched members subjected to combined tension and bending. A method for evaluating the flow stress from the stress intensity versus displacement chart is also described. The flow stress of the notched ductile materials followed the upper-bound solution regardless of the load history. The effect of the combined loading on the flow stress was considered using both the tangent intersection method with the evaluation chart. A method for evaluating the flow stress from the distribution of plastic collapse load on the upper-bound solution is given. The proposed a method showed that this flow stress is in fairly good agreement with that obtained by the upper-bound solution.Copyright

Plastic Collapse of a Notched Austenitic Stainless Steel Specimen Under Combined Tension and Bending

The present paper describes a method for evaluating the collapse load from the tension- and bending-displacement charts. The plastic constraint factor, the collapse load and the 0.2% proof strength all exceeded the upper bound solution. The two collapse mechanisms observed are tension and bending collapses. Interaction of tension and bending results in a larger collapse load than that obtained from evaluating photo-plastic fringe, especially under simultaneous tension and bending loadings. The maximum load yielded more easily the test collapse load than the two-elastic-slope method.

Load History Effect on Plastic Collapse in a Single-Edge Notched SUS316 Subjected to a Combined Tension and Bending

This paper is evaluates the effects of load history on the plastic collapse load of stainless steel members with a single-edge notch. It considers, both the tension force due to an internal pressure and the bending moment caused by an earthquake, considered as load cases for a structure. Experimental equipment was specially developed to cope with the indeterminate problems in fracture mechanics. In this experiment, the stress state of a plastic collapse point was assessed using a membrane stress and axial displacement chart as well as a bending stress and deflection angle chart, which is well known as the ligament method. As a result, we successfully developed a new method for assessing plastic collapse under a complex load. We found that a different load history affects the formation of the plastic region and the collapse point position. The effects of load history on the plastic collapse load were not very big.Copyright