Papers by Keyword: Mixed Mode

Abstract: Mixed mode (I/II) loading conditions occur frequently in the asphalt layers of pavements. Therefore, a low-temperature fracture analysis based on mixed mode loading turns out to be of utmost importance. In this research, asphalt concrete (AC) mixtures were prepared using two aggregate gradations and PG58-22 bitumen. AC beams were produced by the mixtures and notch offset values of 48 mm, 75.2 mm, and 107.2 mm were fabricated in the beams in order to be tested in a modified single-edge notched beam (SE(B)) setup. The tests were carried out at two temperature levels of-5 °C and-15 °C. Using the modified SE(B) setup and capturing and processing digital imaged from the growing crack during the tests, fracture resistance curves (R-curves) in mixed mode (I/II) conditions could be constructed for each mixture. The results revealed that increasing the mode mixity and impairing the tensile mechanism in the fracture of asphalt beams could significantly contribute to higher fracture resistance of the mixtures. Mixtures with the highest mode mixity exhibited greater crack tip blunting energy by up to 25%. Similarly, energy dissipation in the unstable crack propagation zone is also increased being a desirable characteristic in post-peak performance of the mixtures.

Abstract: The fatigue crack growth rate is the most important factor in predicting the life of a product when applying the damage tolerance design concept. Studies related to pure mode I for structures under fatigue loading have been actively conducted, while not many studies are conducted on the mixed mode. In this study, therefore, mixed mode fatigue crack growth experiments were designed using the Compact-Tension-Shear (CTS) specimens and the loading devices, proposed by Richard. Furthermore, the finite element analysis was used in determining the stress intensity factors of CTS specimen. As the results, the fatigue crack growth rate using the equivalent stress intensity factors proposed by previous researchers was lower than that of pure mode I at the initial stage of crack growth when the load angle increases.

Abstract: Mixed mode loaded fatigue specimens are not used very frequently. The main reason is that there are still very few qualitative results, which would help with better understanding of how the mode II and mode III are affecting the overall crack propagation. On the other hand, there is considerable number of parts loaded in mixed mode. Studying fatigue failure of roller bearing elements made of polymer material was a motivation to design a new experimental specimen for study of fatigue behaviour of the material loaded in mixed mode. The contribution presents developed FEM model of such specimen with focus on determination of fracture mechanics parameters of propagating cracks.

Abstract: Accurate description of creep crack stress field is very important to characterize the creep crack growth of the structures at elevated temperature. In general, the crack mode in practical engineering practices is not mere the mode I or mode II, and it is the mixed mode. The mismatch effect in weldment is also concerned by many researchers, however, there is no available literatures to discuss the stress field of mixed mode creep crack yet. The overall aim of this paper is to investigate and qualify the distribution of stress field for the mixed mode creep crack. In this paper, a mixed mode creep crack within the mismatched plate is discussed. The stress distribution of mixed mode creep crack are given in this article. With the definition of mode mixity for creep crack, the influence of mode mixity on the stress field is presented. The influence of mismatch effect on the principal stress, open stress and shear stress for mixed mode creep crack is also figured out. The main factor leads to the variation of creep crack tip stress field for mixed creep crack is analyzed. Some useful guidelines are proposed for the engineering purpose of integrity assessment for the structure at high temperature.

Abstract: Creep crack within weldments are very common in engineering practices, and the cracking location in these welding structures always appears at the HAZ location. The mismatch effect on the mixed mode creep crack is still not clear in these available literatures. The aim of this paper is to investigate the mismatch influence on the creep crack of mixed mode thoroughly. A mixed mode creep crack within HAZ is established in this paper. The leading factor that dominates the creep crack tip field under mixed loading mode is studied. The influences of mismatch effect on mode mixity, stress distribution and stress triaxiality are proposed. The difference of mixed mode creep crack and normal mode I or mode II creep crack are compared. The influence of mixity factor on the transient and steady state creep of crack tip are also analyzed.

Abstract: A failure criterion is proposed for ductile fracture in U-notched components under mixed mode static loading. The Compact Tension Shear (CTS) is the preferred test specimen used to determine stress intensity factor in the mode I, mode II and the mixed-mode fracture. In this work, the mode I and mode II stress intensity factors were computed for different notch ratio lengths 0.1<a/W<0.7, of the inner radius of notch 0.25mm<ρ<4mm and load orientation angles 0°<α< 90° using finite element analysis. However, a review of numerical analysis results reveals that the conventional fracture criteria with only stress intensity factors (NSIFs) Kρ first term of Williams’s solution provide different description of stress field around notch zone comparing with results introduce the second and third parameter T-stress and A₃.

Abstract: The paper is dedicated to experiments on near-threshold fatigue cracks under mixed-mode II+III in the ARMCO iron. The mixed mode crack growth was described using an equivalent factor ΔJeff,eq=(1-α)ΔJeff,eqII+αΔJeff,eqIII. The most appropriate description was found for α = 0.67 indicating that the mode III component should be more efficient than that of the mode II which is in contradiction of a ΔK_eq–based analysis. This result shows that, unlike in the austenitic steel, the difference in the efficiency of modes II and III in the ARMCO iron is very small.

Abstract: Elasto-optic constant is an important parameter for stress measurement by digital gradient sensing method (DGS). In this paper, Elasto-optic constant is measured using an edge-cracked three-point bending specimen. Elasto-optic constant is related to known stress intensity factors and specimen thickness. The full-field angular deflections around the crack-tip are measured using DGS. And then Elasto-optic constant were calculated from the experimental data by linear-least squares method.

Abstract: Structural failure of aircraft wings due to nucleation and propagation of cracks is one of the main reasons for failure of aged aircrafts. Reported studies on aircraft failures indicate that the main cause of wing failure is due to fatigue cracks which nucleate from the wing root region. Thus, determination of residual life of the cracked wing structure using fracture mechanics approach becomes important. In the present work an attempt has been made to estimate the SIF of single and multiple cracks in an aircraft wing subjected to lift force. Crack depth ratios ranging between 0.1 and 0.4 and aspect ratios of 0.6 and 1.0 have been considered. Single and multiple cracks are introduced at the wing rib region and the lift force is applied at the bottom surface of the wing. Geometric correction factor (Y) is estimated with the additional consideration of mode II and mode III fracture. The effect of crack depth ratio and number of cracks on SIF is determined. Non symmetric SIF distribution is observed with increase of crack depth ratio. It is also noted that SIF values are always higher at the crack surface region compared to crack middle region irrespective of crack depth ratio.

Abstract: Multi-CPU[1] parallel computing system [2] with mixed modes is the product of parallel computing idea. Control system cannot guarantee real-time control performance due to limitation of computing speed while utilizing complex control algorithms, so operating efficiency of the system needs to be solved. High-speed computing [3] system is needed. Parallel algorithm [4][5] is an effective way to improve computing speed. Mixed-mode parallel computing system is a hardware platform with multiple parallel computing modes. Users can directly change the connecting mode between computing modules through jumper, and the diversity of communication modes provides solutions for various problems.