Deep penetration of low velocity metal penetrators into ice

The paper summarizes the results of research of the destruction of an ice block with cylindrical and spherical penetrators at low velocity (≤325 m/s). The behaviour of ice at high strain rates is described by an elastic–plastic model of continuum mechanics. Numerical modelling of penetration is performed with IMPACT computer code. Algorithms of splitting nodes and destroying elements in a Lagrangian numerical method were modified to solve problems of penetration and perforation. The fracturing is described by a deterministic fracture model. Crack paths are examined; the damage is predicted and compared with existing experimental results. It was found that in the subsonic range of initial velocities the penetration time did not exceed 0.3 ms. Examination of the penetrators’ shapes showed that they were not plastic deformed.

Modeling Crack Growth in ASME Section XI Flaw Evaluations

Rules for assessment of flaws found as a result of periodic in-service examinations of nuclear components, first appeared in Section XI of the ASME Boiler and Pressure Vessel Code in 1974. Since that time, literally hundreds of evaluations have been completed, which have allowed flaws that met the required margins to be accepted for continued service without repair. The flaw evaluation process of Section XI involves prediction of the future growth of such flaws, and then comparison with a calculated allowable flaw size for the location of interest. The crack growth models to be used for such evaluations are generally contained in the ASME Code itself, in Section XI Nonmandatory Appendices A or C, or the new Nonmandatory Appendix Y for Crack Growth Rate Curves (2021 Code Edition), depending on the application and material type. Occasionally, Code Cases are also used to provide recommended crack growth models. The philosophy that has been followed by the Code since its inception has been to model crack growth as accurately as possible, so as to make an accurate prediction of future flaw growth, and then compare the predicted final flaw size with the allowable flaw size for the area of interest, after a margin has been applied. Therefore, the margin is applied only once, so it is easily identified, and is not “double-counted”. The goal of this paper is to summarize the background and basis behind the ASME Section XI general philosophy of the use of a best estimate, or mean, treatment of the crack growth models in Section XI of the ASME Code. This paper will discuss the various approaches that are available to characterize crack growth, and then discuss the approaches which have been used in ASME Code Section XI flaw evaluation rules over the years.

On the Fatigue and Fracture of Bladed and Integrally Bladed Rotors of Aircraft Engine Compressors

The fatigue and fracture for bladed and integrally bladed rotors (IBR) of aircraft engine compressors has been studied. For IBRs, a new distinct finite element technique was developed to model crack propagation under combined low cycle and high cycle fatigue loading. The crack trajectory, aspect ratio, and shape resulting from the method agreed very well with airfoils which fractured in service. The technique can be extended on other compressor disk applications. For bladed rotors limited by fretting fatigue, a unique fracture mechanics based methodology was developed for obtaining an evolved coefficient of friction (COF) resulting from fretting motion between the fan blade and hub. The predicted nucleation location, nucleation life, crack trajectory, shape and propagation life agreed well with the fractured components. The study confirms that the fretting-specific modified Smith-Watson-Topper (SWT) parameter more accurately predicts the nucleation location and life of the crack compared to the plain fatigue SWT parameter.

On the Fatigue and Fracture of Bladed and Integrally Bladed Rotors of Aircraft Engine Compressors

The fatigue and fracture for bladed and integrally bladed rotors (IBR) of aircraft engine compressors has been studied. For IBRs, a new distinct finite element technique was developed to model crack propagation under combined low cycle and high cycle fatigue loading. The crack trajectory, aspect ratio, and shape resulting from the method agreed very well with airfoils which fractured in service. The technique can be extended on other compressor disk applications. For bladed rotors limited by fretting fatigue, a unique fracture mechanics based methodology was developed for obtaining an evolved coefficient of friction (COF) resulting from fretting motion between the fan blade and hub. The predicted nucleation location, nucleation life, crack trajectory, shape and propagation life agreed well with the fractured components. The study confirms that the fretting-specific modified Smith-Watson-Topper (SWT) parameter more accurately predicts the nucleation location and life of the crack compared to the plain fatigue SWT parameter.

Crack Initiation Behaviors of Granite Specimens Containing Crossing-Double-Flaws with Different Lengths under Uniaxial Loading

Crack initiation is an important stage in the failure process of rock masses. In this paper, crack initiation behaviors (crack initiation model, crack initiation location, crack initiation angle, and crack initiation stress) of granite specimens containing crossing-double-flaws with different lengths were investigated using PFC2D software. Crack initiation models were all tensile wing cracks, which did not exactly initiate from the main flaw with a length of 30 mm. They can initiate from the secondary flaw with a length 20 mm at α of 30° (included angle between main flaw and horizontal direction) and β of 90° (included angle between main and secondary flaws) and from main and secondary flaws at α of 30° and β of 60°. These were mainly induced by the superposition of stress fields around the main and secondary flaws as β varied from 0° to 90°, especially the tensile force concentration zones superposition. The tensile forces concentration zone around flaw shrank towards flaw tips with the increase of flaw’s inclinations measured horizontally. Under stress field superposition effects, the crack initiation stress decreased firstly and then increased with β at α of 30° and 45°. Crack initiation locations were close to flaw tips but not restricted to them. The distances between crack initiation locations and flaw tips, and the crack initiation angles depended on the flaw where first macrocracks initiated from. Microdisplacement field distributions of granite specimens to reveal the mesomechanism of crack initiation behaviors were discussed.

Micromechanical Modeling for the Damage Accumulation and Adhesive Wear of Metallic Materials Containing Inclusions

Metallic materials usually contain some amounts of inclusions which are known to affect their mechanical properties since the bonding strength of the matrix–inclusion interface is relatively low, voids or cracks are thus easily formed under a tensile loading. However, under a contact loading, the effects of subsurface inclusions on the sliding wear of metallic materials are not thoroughly understood. In this work, a micromechanical model is proposed to study the shear fracture and wear of metallic materials containing random inclusions. With the model, crack branching and crack aggregation during contact loading are simulated, and the formation process of sheet-like wear particles is clarified. It is demonstrated that the subsurface micro-cracks, particularly those near inclusions, and their subsequent evolution play a major role in the adhesive wear. This investigation is helpful in understanding the adhesive mechanism of wear, and the proposed model could be a promising approach for the prediction of adhesive wear.

KAJIAN EKSPERIMENTAL POLA RETAK PADA SAMBUNGAN BALOK-KOLOM BETON PRACETAK DENGAN MENGGUNAKAN SAMBUNGAN KERING

There is a major problem in the installation of precast concrete system, namely connection. Connection on precast system must have strength that can withstand the loads that occur. One of the system used in precast concrete connection is by using dry connection method. Dry connection is a connection between precast concrete element using a steel plate as a connector, which is bolted or welded. Judging from the connection problems in precast concrete, a study was conducted to observed the behavior of precast beam-column connection observations are also made to analyze a collapse model, and a crack pattern between the joints of the beam-column precast. Keywords: precast concrete, dry connection, collapse model, crack pattern