This effect is generally handled by basing the crack initiation life prediction on a modified (lowered) strain-life or stress-life curve that includes the effect. In 1960 Schijve  observed that experimentally derived crack growth equations were independent of the loading sequence and depended only on the stressintensity range and number of cycles for a given portion of loading sequence. The central problem in the successful utilization of fracture mechanics techniques applied in a fatigue spectrum is to obtain a clear understanding of the influence of loading sequences on fatigue crack growth. Of particular interest in the study ofcrack growth under variable-amplitude loading is the decrease in growth rate called crack growth retardation that usually follows a high overload. Most of the reported theoretical descriptions of retardation are based on data fitting techniques, which tend to hide the behavior of the phenomenon. If the retarding effect of a peak overload on the crack growth is neglected, the prediction of the material lifetime is usually very conservative . The small scale yield model employs the Dugdale  theory ofcrack tip plasticity, modified to leave a wedge of plastically stretched material on fatigue crack surfaces. Fatigue crack growth was simulated by Skorupa and Skorupa  using the strip model over a distance corresponding to the fatigue crack growth increment as shown in Fig. 1.
Experimental studies reveal that fatigue crack growth rates (FCGR) in welds may display strong sensitivity to welding process, weld geometry, localized changes in material and mechanical properties of the weldment, including the heat affected zone. These effects arise from the complex interplay between macroscale fea- tures (crack size and geometry, material properties including weld strength mismatch, weld residual stresses, load ratio, etc.) and the micromechanism of fatigue crack growth. At the macroscale re- gime, there is a clear correlation between crack propagation rate under cyclic loading and load ratio (R) in which the FCGR increases with R. Here, crackclosure effects play a key role in controlling the rate ofcrack propagation with varying load ratios by strongly affecting the (effective) stressintensity factor (SIF) range. However, despite the technological importance of fatigue crack extension in welded structural components, a full understanding of the fatigue crack growth phenomenon in welds remains limited as does a more extensive body of experimental data. Early work of Benoit et al.  on fatigue crack propagation in the heat affected zone (HAZ) for a structural steel weld showed that FCGR in welded materials are lower than the corresponding rates in the base plate material. Link  conducted FCGR experiments using compact tension specimens for both the base plate and weldments of a 5456-H116 aluminum alloy and an ASTM A710 Grade A steel with and without post-weld heat treatment (PWHT); these results show a strong influence of welding residual stresses on the measured FCGRs due to the effects ofcrackclosure. Later, Shankar and Wu  showed that fatigue crack growth behavior in welded 5083- H321 aluminum alloys is essentially similar to the parent material. These previous research efforts clearly demonstrate that accurate evaluation procedures for effective stressintensityfactors which are applicable to welded fracture specimens remain essential in more refined defect assessment procedures capable of including ef- fects ofcrackclosure on fatigue crack growth rates.
Consider a square plate, with a single crack normal to one edge, as represented in Figure 5. The crack length is denoted by a and the ratio between the height and the width of the plate is given by h/w = 0.5. The plate is loaded with a uniform traction t = σ, acting now in a direction parallel to the crackand applied anti-symmetrically at the sides which corresponds to a sliding- mode loading. This is a very difficult case, for which there are no published benchmark results, as far as the authors knowledge is concerned. Therefore, results have been obtained with the present formulation, in order to be compared with those obtained by the dual boundary element method and the J-integral technique, using the software . This combination of the dual boundary element method with the J-integral technique is an extremely-accurate tool because it uses the elastic field computed at internal points which is a highly accurate operation in the boundary element method due to the fundamental solutions. Five cases were considered, with a/w = 0.2, 0.3, 0.4, 0.5 and 0.6, respectively. A convergence study was carried out with three different meshes; convergence was achieved, for all the five cases ofcrack-length considered, with a mesh of 512 finite elements, in which the discretization was refined around the tip. The results obtained with this finite element mesh, presented in Table II are remarkably accurate; the present results match those obtained with the dual boundary element method and the J- integral technique within two decimal places. It is important to note that the stress-intensityfactorsof the opening-deformation mode are always below 10 −3 , since this is mainly a sliding-
resistance to fracture in the design of structural members. ASTM standards E399 and D5045 give some guidance for plane strain mode-I fracture toughness for metals and plastics, respectively. No standard requirements exist for the validity of linear elastic fracture mechanics and plane-strain conditions for tests with polymeric materials under mode-II and mixed-mode loading conditions. Therefore, it may be necessary to develop tests tailored for use with polymeric materials in order to investigate the role of mixed-mode loading conditions. This investigation seeks to extend under- standing of the polymeric materials fracture behavior under mixed-mode loading conditions through numericaland experimental analysis. Using finite element results, correction factors were applied to the specimen and a polynomial fit was proposed to evaluate the stressintensityfactorsof the spec- imen with a crack subjected to mixed-mode loading conditions. The research conducted for this study assumed that the polymeric material under consideration was homogenous and linear elastic. The main objective of this study was to determine the fracture toughness K IC and K IIC for the pol-
This finite element appears as an attractive tool for definition of the stress field along notched surface shell element decoupled from the one-dimensional element proposed. Once defined the stress field along the edges of the component part containing notches, an approached procedure can be carried out even without a subsequent finite element analysis, using published graphical results (Harris 1997). The displacement field of the finite shell element results from the superposition of the rigid beam displacement and a complete Fourier terms development. The deformation model considered is a semi-membrane strain field, (Fonseca et al 2006). The SIF determination in a crackopening mode is function of an equation presented by (Harris 1997) from Neuber’s stress concentration factors in straight components as follows:
Latin American Journal of Solids and Structures 11 (2014) 1886-1905 In ANSYS PLANE 82 elements are used. A concentration keypoint is generated at the crack tip. KCALC command is used for determinationofstressintensityfactors after the local coordinate system is defined and used at the crack tip and the crack path defined in the post processer using path operations. The model ofcrack eccentric in x-direction as modeled using ANSYS is shown in Figure 4. It is clear from Figure 5 that quarter point elements exist near the crack tip.
Figure 7 illustrates the correlation between CMOD and CTOD for different notch locations. A nonproportional behavior may be observed when the notches are taken off-center. This effect in- creases as the notch tends to move towards the support span. It is associated with mixed mode condition, in which the effect of sliding mode-II in fracture is accentuated. It is important to em- phasize that, in the present work, CTOD values were obtained directly. However, the indirect measurement of CTOD is usually determined by measuring the value of CMOD, considering linear relationship between them. Therefore, the use of DIC method has been proved to be useful to measure CTOD.
eneral aspects of the concept based on calculation of the average stress over the length of the process zone are described in Refs. [1-6] for a solid with cracks or notches. These references demonstrate an advantage of the critical average stress criterion over the classical elastic and elastic-plastic fracture mechanics criteria because this criterion avoids the confusion of applying the unrealistic continuum mechanics stress singularity to the fracture process zone in the vicinity of the crack (or notch) tip. For example, the failure criterion of the average stress within an effective distance has been successfully employed to relate the apparent fracture toughness in specimens with notches to the fracture toughness obtained from deeply cracked specimens (e.g., ). In this case, the effective distance corresponds to the point with a minimum of the stress gradient which requires finite element analysis to obtain the effective distance . It should be noted that the effect of the high stress gradient ahead of the crack/notch tip can be taken into account by means of the theory of critical distance using the stress at some critical distance . The theory of critical distances was very successful in predicting the fracture strength of ceramic materials.
In this research, fatigue crack growth da/dN x ∆ K has been studied in two dual-phase steels broadly used in the automotive industry, with 7% to 12% of martensite volume fraction. The main difference between the steels is the chemical composition: one of the steels has chromium additions while the other has silicon as an alloy element. Besides the chemical composition, the effect of 10% of prestrain followed by a bake hardening heat treatment on the fatigue resistance was verified. This thermo-mechanical treatment was used to simulate the stamping and the paint baking of the wheels. C(T) specimens with 3.80 mm thickness and 50 mm width in T-L orientation were used for the experiments. Testing frequency was 30 Hz. The experiments were performed in ambient air (approximately 25ºC, R.H. = 60% ), at R stress ratio of 0.1. In the near-threshold ∆ K th region and in the final rupture region, the fatigue behavior
While curvature is being decreased, the total number of atoms does not remain the same, this leads to affect the total potential energy of the system. Increasing the number of removed atoms to decrease the sharpness is the reason of decreasing the yield point. To gain higher curvatures we remove atoms of the right and left sides of the void. These atoms _as shown before_ feel almost no stress, but their removal leads to a decrease in the yield point. Removing these atoms or any atoms in the specimen changes potential energy and this will cause the system failure. So it seems that the yield point is more sensitive to the total number of removed atoms than the stress concentration of the sample.
Based on the impressive increase in the number of dependent elderly persons, and in view of the institutional incapability of meet these needs, the informal caregiver has emerged as a key figure in the promotion of quality of life in a situation of de- pendence. Playing this role is not an easy task and it is accompanied by sociocultural difficulties that go beyond the psychological and physical demands al- ready existent in the activity of informal caregiving. With respect to the definitions of caregiver and in- formal caregiver presented by the literature, there are many and not all are unanimous as regards reference to the concepts. In general, when the types of care- givers are specified, the main (or primary) caregiver is defined as the person who has the greatest responsibil- ity in the daily care of the dependent elderly person, performing the majority of day to day tasks; and the secondary caregiver, as the one who performs tasks without much regularity, and without having much responsibility or power of decision, helping the main caregiver only with complementary activities. (3,4) Sec-
The transition to kindergarten is a part of family life cycle and an expected devel- opmental change that can induce stressand as such requires family adjustment. In this paper we deal with the types and sources of parental stress when a child enters the kindergarten and during the period of his/her adaptation. In the first phase of the study we conducted three focus group discussions, in which 20 parents participated. The second phase was designed for the questionnaire survey, in which the sample consisted of 163 parents. The data suggest that in parents’ experience the most fre- quent are stressful events related to the child’s reactions and changes in the child’s acquired habits. With less frequency parents reported about stress related to their own emotional reactions and changes in the family functioning. When compared, no significant differences were found between the fathers and mothers in terms of the frequency of the reported stress. Generally, parents estimate that stressful experience associated with children’s adaptation to kindergarten does not induce highly intense stress. Additionally, we found that mothers perceive the children’s period of adapta- tion to kindergarten significantly more stressful than fathers. Research findings can be important for future investigations about the effects of parental stress in the pe- riod of children’s adaptation to kindergarten on optimal family functioning, and for the practical implications for working with these families.
horn microtip diameter, 10 mm. Standard flavonoids solutions of 8.0 m g/mL were mixed in same volumetric flasks and 30 ml of mixtures were kept in brown glass tubes (3 cm in diameter; 10– 20 cm in height). The tubes were immersed in a low-temperature water bath (DC–1006, Safe Corporation, Ningbo, China) to maintain a constant temperature. Five solvents were chosen not only because they are frequently reported for extraction flavonoids, but also they may cause different sonochemical effect. Additionally, we want to know whether flavonoids stability would be affected when ultrasound intensity or temperature changes. The solutions were then treated by US with the following parameters (except for the tested factor): probe position, 1 cm from the top of the extraction cell; liquid height (the distance from the horn microtip to the bottom of the tube), 4 cm; temperature, 5uC; pulse mode: on, 2 s and off, 2 s; treatment time, 20 min; and US intensity, 15.29 W/cm 2 . Samples obtained by standing under the same conditions were used as controls (CK). The ultrasound treated samples (US) and CK solutions were filtered through 0.45 m m polyvinylidene fluoride microfiltration membranes (Shanghai Xingya Purification Material Co., Shanghai, China) and subsequently stored at –18uC for further HPLC analysis.
Objective: The aim of this study was to assess whether repetitive openingandclosureof self-ligating bracket clips can cause plastic deformation of the clip. Methods: Three types of active/interactive ceramic self-ligating brackets (n = 20) were tested: In-Ovation C, Quicklear and WOW. A standardized controlled device performed 500 cycles ofopeningandclosure movements of the bracket clip with proper instruments and techniques adapted as recommended by the manu- facturer of each bracket type. Two tensile tests, one before and one after the repetitive cycles, were performed to assess the stiffness of the clips. To this end, a custom-made stainless steel 0.40 x 0.40 mm wire was inserted into the bracket slot and adapted to the universal testing machine (EMIC DL2000), after which measurements were recorded. On the loading portion of the loading-unloading curve of clips, the slope fitted a first-degree equation curve to determine the stiffness/ deflection rate of the clip. Results: The results of plastic deformation showed no significant difference among bracket types before and after the 500 cycles ofopeningandclosure (p = 0.811). There were significant differences on stiffness among the three types of brackets (p = 0.005). The WOW bracket had higher mean values, whereas Quicklear bracket had lower values, regardless of the opening/closure cycle. Conclusion: Repetitive controlled openingandclosure move- ments of the clip did not alter stiffness or cause plastic deformation.
half-plane is assumed to constant along the lateral direction. The problem is reduced to a system of singular integral equation of the second kind which is solved numerically to compute the contact stress distributions. In order to provide more insight into the behaviour of the functionally graded steel, contact mechanics analysis is also conducted by means of the inite element method. The parametric analyses are performed by considering lat punch proiles. The presented results illustrate the inluences the coeficient of Coulomb friction on the distributions of the contact stresses andstressintensityfactors.
Analysis of Fracture Mechanics problems considering cracks with arbitrary shapes and mixed crackopening modes: another important contribution of this work consisted in the extension of the Splitting Method to the analysis of problems containing cracks with arbitrary shapes, as explained in Chapter 2. Obviously, when cracks with arbitrary shapes are considered, mixed crackopening modes must be also taken into account. When such modeling is available, complex real-life problems can be analyzed, with emphasis on multisite damage problems. For instance, it was possible to find out the most critical pattern of cracks attached to holes in a rivet connection.
Sensitivity analysis was conducted each time for the model described in Section 3, for which it was assumed that the parameters vary in ranges given in Table 1. Table 2 lists parameters influence of which was not taken into consideration in sensitivity analysis. According to the fact that these parameters are connected with the phase change diagram, they cannot be changed freely and independently from one another. Additionally, in Table 2 physical parameters of the mould are included. Table 2.
Attractive technological paraphernalia is available, from which we can really benefit, but they can also cause more harm than good. Different processes, but intended for similar purposes, were used in the past, such as the construction and ornamentation of the pyramids that housed the bodies of sovereigns (identified with the gods), their belongings, and even servants and pets, hoping that they could return to use them in another life. Temples were filled with icons that kept “staring” at those being honored, reinforcing the memory of their presence in the world of the living. It was a ritual meant to ensure that death had come and the life within the body was gone, which only represented a brief passage through the path towards eternity.