Artificial Surface Defects Research Articles

直流電位差法による５０５２アルミニウム合金の表面疲労き裂サイズの評価

The quantitative evaluation of the surface fatigue crack size initiated from an artificial surface defect has been attempted using a DC potential drop (DCPD) technique for an aluminum alloy. A 5052–H34 aluminum alloy sheet with a small blind hole as a surface artificial defect has been used. Potential drop defined as a function of crack area and the correction factor α obtained from experimental data have been used in order to estimate crack depths. The estimated crack depth was slightly smaller than the actual crack depth. The measurement accuracy will be improved by increasing the sensitivity of potential measurement. The surface crack initiated from the artificial surface defect propagated with an almost constant aspect ratio a/c (a: crack depth, c : half crack length) after the crack reached the bottom of the artificial defect under the condition employed in this study.

人工表面欠陥を有するAl–Mg系合金板材の3%NaCl水溶液中の表面疲労き裂伝播挙動

The surface fatigue crack propagation behavior has been investigated under tension-tension cyclic stress at two different frequencies in 3 mass% NaCl aqueous solution for the 5052 and 5083 aluminum alloys, and 1100 commercially pure aluminum sheets with an artificial surface defect. While the fatigue life (number of cycles to failure) at low frequency is obviously longer than that at high frequency in 5083 alloy and 1100 aluminum, the fatigue life is almost independent of the frequency in 5052 alloy. The reduction of fatigue life is largest for 1100 aluminum containing almost no addition of Mg which generally improves corrosion resistance of an aluminum alloy. The fatigue life for 5083 alloy, which is assumed to have β phase more than 5052 alloy because of differences in Mg content and heat treatment, is lager than that for 5052 alloy. In the early stage of fatigue crack when propagation is governed by corrosion environment, surface crack propagation rate at low frequency tends to be slightly higher compared with that at high frequency for 5052 alloy. Further, the 5052 alloy exhibits the flatter front shape of fatigue crack at failure at the lower, because the surface crack propagation is more accelerated by corrosion effect.

Effect of artificial surface defects on failure of steel plates in contact loading by explosion of a layer of explosive substance

The results are presented of experiments carried out to examine the failure of thick plates with stress raisers under explosion loading. Recommendations for selecting the dimensions of a charge of an explosive substance for carrying out operations on nonstandard plates are experimentally justified.

Size and shape of the critical structural defect in polystyrene and polymers reinforced with rubber

The effect of a critical structural defect on the strength of polymers under conditions of impact loading is considered. With PS, toughened PS and an ASB plastic, the size and shape of the critical structural defect have been determined using the method proposed previously. The size of the critical structural defect is related to the polymer's supermolecular structure. It is concluded that polymers with a rounded critical structural defect have enhanced sensitivity to artificial surface defects.

ELECTRICAL POTENTIAL MONITORING OF CRACK FORMATION AND SUBCRITICAL GROWTH FROM SMALL DEFECTS

Abstract —An experimental method was developed to quantify the formation and subcritical propagation of small cracks emanating from artificial surface defects. Continuous crack depth information was obtained from dc electrical potential measurements employing an analytical model. Fatigue experiments were conducted to evaluate the crack monitoring procedures for conditions relevant to the elevated temperature defect tolerance of superalloys. Cracking progressed uniformly and predictably from small surface defects (0.1 mm deep and 1.4 mm long) in A286, 304 and 10Ni steels and in René 95 and MP–159 superalloys. Crack depths, computed based on analytical calibration of measured electrical potentials, agreed to within ±18% of corresponding values measured optically. Similar results were obtained for a penny‐shaped defect, 75 μm deep. Applications of the technique were investigated, including characterizations of fatigue crack formation and growth in René 95.

Second Paper: An Investigation into the Effects of Pre-Heat Temperature on Ductility in a Warm Heading Process

Two-stage warm heading operations were carried out on a mild steel and three high tensile bolt materials (types 1, 2 and 4 from B.S. 3111:1959) at pre-heat temperatures in the range from ambient up to 600°C. The tests were carried out in the form of a transfer process (approximately 2 seconds delay between stages) and also as an interrupted process (approximately 30 minutes delay between stages). Artificial surface defects of various depths were machined on the heading specimens to aid measurements of the change in ductility with increase in pre-heat temperature. The method consisted of estimating the critical depth of groove which would be just on the point of fracture at the end of a particular heading operation. The steels tested were found to have low ductility at pre-heat temperatures in the range from 200°C to 300°C; at a pre-heat temperature of 600°C the steels exhibited extremely high ductility. The results suggest that rolled bar of relatively poor surface quality could be warm headed at 600°C without fracturing. A solid film of colloidal graphite and a high chlorine oil were both found to be satisfactory lubricants at all specimen pre-heat temperatures up to 600°C.

The Development of an Apparatus for Providing Artificial Surface Defects on Inside Surface of Cladding Tubes

It is important from the viewpoint of reactor safety as well as from economical interest to determine the limit of allowable depth and length of surface defects on fuel cladding tubes. For the purpose of preparing cladding tubes provided with artificial defects of various degrees to be used as standard reference specimens for internal pressure burst tests, an apparatus has been developed for plowing troughs of predetermined depth and length on the inside surface of cladding tubes. This apparatus is capable of cutting such troughs in the center of a cladding tube 100 cm long, and the depth of the scratched defect can be measured nondestructively with the use of a measuring instrument provided with stylus. The paper presents an outline of the apparatus together with some experimental results.

The Development of an Apparatus for Providing Artificial Surface Defects on Inside Surface of Cladding Tubes

It is important from the viewpoint of reactor safety as well as from economical interest to determine the limit of allowable depth and length of surface defects on fuel cladding tubes. For the purpose of preparing cladding tubes provided with artificial defects of various degrees to be used as standard reference specimens for internal pressure burst tests, an apparatus has been developed for plowing troughs of predetermined depth and length on the inside surface of cladding tubes. This apparatus is capable of cutting such troughs in the center of a cladding tube 100 cm long, and the depth of the scratched defect can be measured nondestructively with the use of a measuring instrument provided with stylus. The paper presents an outline of the apparatus together with some experimental results.

Fracture Behavior of a Model Brittle Solid Containing Artificial Surface Flaws

Fracture Behavior of a Model Brittle Solid Containing Artificial Surface Flaws