Validation Testing and Analysis of Cracked-Hole Continuing Damage Solutions

A simple simulation of alternate growth of a small surface crack in the surface and depth directions was performed to illustrate the changes in crack aspect ratio, induced by grain boundaries, as a function of crack size. It is shown that at small crack sizes, large variations in aspect ratio, a/c (a is the crack depth and c is the half-surface length), occur, due to local crack front perturbations induced by grains that are oriented for crack growth. At these crack sizes, the assumption of a semicircular crack shape (a/c=1.0) was found to cause errors in stress intensity range (ΔK) calculations. This, in turn, led to significant scatter or “anomaly” in small crack growth rates relative to large cracks. At large crack sizes, the effects of local crack front perturbations on crack aspect ratio and ΔK were found to be insignificant. As a result, the scatter in crack growth data was found to decrease to a negligible level at large crack sizes. It is suggested that the limiting crack size above which the small crack behaves as a large crack, l2=10d (d = grain size), proposed by Taylor and Knott, is related to the crack size above which the effects due to aspect ratio variations are small.

: Research about the development of Science Process Skills (SPS) has been carried out as SPS measuring instrument study materials in Biology subject at 11 th grade of senior high school. The study is aimed to produce a valid and practical test instrument of SPS. The method used in this research is Development Research (DR) method which refers to the instrument development model from Djaali and Mulyono (2008). The steps of the research and development consist of several phases: synthesis theory and requirements analysis, design stage (variable construction, development of indicators, the preparation of the lattice matter, writing of instruments, scoring) and the evaluation phase. Evaluation phase is divided into three: validity test, reliability test and analysis of grain items. The analysis of grain items is done by analyzing the degrees of difficulty, different power and distracters function. The validation of Science Process Skills (SPS) is done in three stages, namely validation theoretical (content experts, constructs experts and linguists) and empirical validation (test participants' answers). Based on the theoretical validation of the results obtained an average value of 4.2 which indicates that the questions of SPS is valid. Practicality of SPS can be detected through the result analysis of the test participants questionnaires in the trial test. The average of the questionnaire practicality while testing is 3.64 which indicate that the question of SPS is a practical category. The results of the analysis from the expert validation test and learner questionnaire showed the SPS that produced is valid and practical. Keywords: Questions development, science process skill, biology learning material

Identification of microscale fracture models for mortar with in-situ tests

The design of a rotorcraft main rotor mast or tail rotor driveshaft is critical to the sizing of many drive system parts, including gearboxes and attachments to the airframe. A reduction in diameter of these parts could result in significant weight savings for the aircraft. Due to the criticality of masts and driveshafts, a damage tolerant design is highly desirable. However, damage tolerance requirements for single load path structures tend to produce heavier parts than those designed using safe-life methods. To alleviate the weight impact without sacrificing safety, the damage tolerant design of the mast and driveshaft must consider all aspects of design. This may include non-planar crack propagation, asymmetrical part-through crack growth, and the effect of surface treatments such as shot peening, carburization, etc. The present research incorporates effects that slow crack propagation into fatigue crack growth analysis, supported by a building-block test program of coupon and element level specimens. The test results show that surface condition influences crack front shape and aspect ratio, and that complex geometry can cause asymmetrical and non-planar crack growth. A NASGRO® simulation of a fillet radius element specimen showed a good correlation with testing results for complex geometry without surface residual stress, and future work is proposed to conduct a fatigue crack growth simulation with the effects of typical surface treatments. Successful prediction of crack growth in masts and driveshafts may lead to substantial weight savings in those parts, and the potential for similar improvements in other affected drive system components.

The stress intensity of corner cracks emanating from holes

Coprime factor perturbation models for closed-loop model validation techniques

To investigate the effect of atmospheric humidity on cyclic fatigue crack growth behavior, fourpoint bending fatigue tests were performed on silicon nitride in laboratory air and toluene. Crack aspact ratios for surface cracks in laboratory air were clarified to be lower than in toluene, The relationship between crack growth rate and maximum stress intensity factor for small surface cracks was obtained using the above crack aspect ratios. This result indicated that crack growth rate was accelerated by atmospheric humidity in the low stress intensity factor range, but not in the high range. This acceleration was clarified to be causes by the mutual action of cyclic stressing and atmospheric humidity. Microcrack initiation ahead of the main crack, the cutting process of ligament between the micro and the main crack, and cyclic loosening of crack bridging at wake of the crack tip were ciarified to be dominant factors which influence the crack growth behavior in both environments.

The excellent durability performance of Glare, a thin fiber metal laminate (FML) material system, is now being proven in service. This has motivated work towards the application of FMLs to thicker structures driven by damage tolerance. In order to fully characterize the crack growth life of such materials, models are necessary that can account for the unique aspects of material systems under consideration, including non-uniformity of composition and stress states, and the resulting complex damage state involved in fatigue crack growth. This thesis presents a generalized analytical model for the prediction of fatigue crack and delamination growth in FMLs of arbitrary lay-up, including differing metal alloys, different thickness layers, and different combinations of reinforcing composite layers. Cracks in each layer, and delaminations in each interface, are allowed to grow separately, with the interactions of the damage throughout the laminate taken into account. The model is structured in a modular and iterative fashion. Modules for determining the load redistribution around damage and the strain energy release rate of delamination have been derived and independently validated through comparison to finite element analyses. A series of tests with thick fiber metal laminates of varied construction was carried out to verify the overall crack growth predictions of the model. While some discrepancies between the results and predictions for the most complex laminates suggest that refinement of the delamination strain energy release rate formulation is needed, many of the test results were accurately predicted, demonstrating the suitability of this model for use in design and analysis of thick FML structures.

Rock burst of deep circular tunnels surrounded by weakened rock mass with cracks

The majority of data on the development of fatigue cracks in tubular joints has come from tests on simple T or Y joints. As part of a joint industry research programme, fatigue tests were carried out on four complex overlapping YT joints. The crack development was monitored using both eddy current and acpd techniques. The crack growth characteristics are presented as a function of the normalised crack growth through the thickness a/af versus the normalised number of cycles to failure N/Nf and as the aspect ratio a/c versus the normalised crack depth a/af. The crack growth rate through the thickness a/al is also determined and the stress intensity factor for the tubular joints inferred from known and accepted crack growth laws. Knowledge of crack development for tubular joints is crucial when planning optimised inspection programmes based on surface crack detection. Knowledge of the crack growth development allows estimates to be made of the associated crack depth and time to failure when a surface crack is detected. Inference of the stress intensity factory for tubular joints allows benchmarking of analytical models to be carried out. The results show that a significant difference in crack development occurs for overlapping joints than for simple joints. Crack initiation occupies more of the total life and through thickness cracking develops much later for overlapping joints compared with simple joints. This variation in crack depth is reflected in the aspect ratio, a much lower value being obtained for the overlapping joints. For the geometries tested, cracking also occurred in the brace wall and not the chord wall. The results allow greater accuracy in predicting time to failure of these joints, once a surface crack is developed. This is of importance in planning optimised inspection strategies and determining how and when to repair detected fatigue cracks. 1.0 INTRODUCTION Fatigue testing of tubular joints has concentrated mainly on the derivation of design life S-N curves for ultimate joint life and ignored, to a certain extent, the study of crack formation and growth. However, development of a reliable system for measuring crack depth during the UKOSRP I programme (1) has enabled greater observations of crack development to be made. Knowledge of the behaviour of damaged components has numerous benefits. It allows analytical models to be modified and benchmarked for accuracy. It also enables understanding of development of damage to final failure for different types of component. This is particularly important in recognising that the way a crack penetrates through a tubular member may vary with joint type. Furthermore, predictions of crack growth rely entirely on growth constants derived from experimental tests under various conditions. In addition to the fatigue crack growth constants, two areas of crack development are of particular interests:the development of cracks through the thickness with respect to type of joint tested, andthe aspect ratio of the crack, defined here as the ratio of crack depth 'a' to the half crack length 'c'.

Up-to-date map data is a must for current and future navigation and advanced driver assistance system (ADAS) applications. Today, digital maps are normally stored on DVDs or hard disks, with periodic updates only available on replacement disks. However, new mechanisms for updating maps have been investigated and some of them already reached the market. As the real world is changing every day, detecting changes to the road network quickly and at a low cost is a challenge. Although mapmakers continuously survey the European road network for changes, map information is not always up-to-date or accurate. This paper presents the test and validation results and two example applications from the FeedMAP project and how they can be used for increasing driving safety by integrating map deviation detection and incremental update technology into ADAS applications using the ADAS Horizon concept.

The propagation and coalescence of numerous discontinuous joints significantly contribute to landslide instability during excavation unloading. The tip expression of stress intensity factors of two collinear unequal length cracks in a typical rock mass under unloading conditions was calculated based on the superposition principle and fracture mechanics to determine the meso-influence law of intermittent joint interaction in the slope under the action of excavation. The effects of many factors on this interaction were also analyzed theoretically. Unloading tests were conducted on rock-like specimens with two collinear unequal length cracks in addition to numerical simulation and theoretical analysis. The results show decreased interaction between the two cracks with increased crack distance, increased influence of the main crack on a secondary crack with increased length of the main crack, and decreased influence of the secondary crack on the main crack with decreased length of the secondary crack. Wing tensile cracks first appear at the tip of flaws, and the propagation of these cracks occurs with the generation of secondary tensile cracks and shear cracks during unloading. Propagation and coalescence between cracks lead to tension and shear mixed failure of a rock bridge, and tensile cracks appear near the unloading surface. The axial initiation and peak stress of a crack increase with increased flaw distance, and the theoretical calculations were confirmed by lateral unloading test results.


 
 
 The purpose of this research is to develop a multi-site damage probabilistic life prediction model that could be used to assess the integrity of engineering structures susceptible to fatigue in presence of neighboring cracks. Both experiments and simulation were used to produce the data required for the model development. The experiments were performed to investigate the interaction of two adjacent semi-elliptical cracks under cyclic loading. A series of tests at different loads and for different crack aspect ratios were conducted under uniaxial constant amplitude fatigue loads on API-5L grade B steel samples. Crack growth rate of two initial semi-elliptical cracks was investigated both on the sample surface and in the depth direction. Moreover, Crack growth and interaction was investigated using a simulation technique that incorporates the stress intensity factor of a single crack with an existing cracks interaction correction factor models from the literature. Finally, a Bayesian inference modeling technique is adopted to estimate the life prediction model parameters, assess any model bias and uncertainty and validate it.
 
 

A generalized model enhancement is proposed to link small‐ and large‐crack growth laws. The enhancement is based on crack growth rate laws with crack tip plastic zone size formulations. Transition functions are used to transform small‐crack plastic zone sizes and crack growth law exponents to those predicted by linear‐elastic fracture mechanics. In doing so, influences on crack growth, e.g. constraint, crack aspect ratio and specimen geometry are accounted for. The applicability of the enhancement is directed toward instances where small cracks start from geometric features and grow through stress gradients to eventually become large cracks under nominal LEFM conditions. The enhancement is applied to the Wang model, and crack growth rate and fatigue lifetime predictions are made. The enhancement is shown to provide a good correlation to experimental results for Ti–6Al–4V under various maximum stresses at a stress ratio of R = 0.4.

Evaluation of the multiple embedded cracks interaction effect in creep regime by creep damage method