This work aims to investigate the anisotropic fracture and energy dissipation characteristics of marbles cored along an angle of 0°, 30°, 60° and 90° with respect to interbed planes, subjected to multi-level cyclic loading conditions. Rock fatigue deformation, strength, lifetime and dissipated energy first decreases and then increases with increasing interbed orientation, they get to the minimum for sample having 30° interbed orientation. Rock stiffness degradation is significant with the increase of cyclic level and the stiffness evolution is affected by interbed structure. The incremental rate of dissipated energy becomes faster with increase of cyclic loading level and it presents an abrupt increasing trend at the last cyclic loading level. A damage evolution model was first established based on the dissipated energy to describe the two-phase damage accumulation characteristics. It suggests that the proposed model fits well to the testing data and favorably represents the non-linear characteristics of damage accumulation.

The fracture behavior of ultra-high temperature ceramic matrix composites at high temperature has received increasing attention. However, few studies consider the effect of particle/crack interaction on the high temperature fracture strength. In this work, based on the energy storage capacity, energy balance method and fracture theory, the effect of particle/crack interaction is introduced into a temperature-dependent fracture strength model of monolithic ultra-high temperature ceramic matrix composites, which also considers effects of flaw size, grain size and residual thermal stress. Furthermore, by considering the influence of the laminated structure, a theoretical characterization model of the temperature-dependent fracture strength of laminated ceramic matrix composites is developed. The effect of particle/crack interaction is also included in this model. It should be noted that the predictions of the models agree well with the experimental data of both monolithic and laminated materials without using any fitting parameters. The effect of particle/crack interaction is found to have a significant weakening effect on the strength of materials at different temperatures. The theoretical models only need some simple basic material parameters to predict the fracture strength and mechanisms of ceramic matrix composites at high temperature, which have important practical significance for engineering applications.

Fatigue behaviour of HIPed and stress relieved Ti6Al4V alloy specimen’s produced by SLM was analysed (Rε = -1). The HIP process caused a microstructural transformation decreasing the hardness and monotonic properties that not allowed fatigue strength increase. A bilinear behaviour in the elastic strain-fatigue life curve was observed, because of Young´s modulus decrease during the cyclic elasto-plastic tests consequence of subgrains formation. The Smith-Watson-Topper and total strain energy density models showed a good concordance between predicted and experimental fatigue lives in notched samples.

The fretting damage and wear debris on the dental implant-abutment interface (IAI) are unclear. In this study, fatigue cycle loading (FT) and chewing cycle loading (CW) test were applied to two implant systems, the fretting damage morphology and wear debris generation on the IAI were observed by a scanning electron microscope. The torque value of the central screw was measured by electronic torque tester. The fretting damage on the IAI was relatively slight and mainly plastic deformation in the FT group, which was more serious and mainly furrow wear in the CW group. Various forms of wear debris were generated. The removal torques were lower than its pre-tightening value in both groups, the decline and loss rate of the CW group was significantly higher. This study confirmed the critical roles of fretting damages and metal wear debris on the IAI in the implant-supported prosthesis.

Fatigue experiments and numerical simulations based on the Linear Elastic Fracture Mechanics (LEFM) theory were conducted on the Even-Matched (EM) and Under-Matched (UM) 10CrNi3MoV Load-carrying Cruciform Welded Joints (LCWJs). The study firstly experimentally investigated the Fatigue Crack Growth Rate (FCGR) of base metal, EM, and UM weldments. The corresponding Paris parameters as essential input data are provided to assess the fatigue crack propagation behavior for weld toe and weld root failure of LCWJs. On the one hand, the Stress Intensity Factors (SIFs) at weld toe and weld root were calculated considering the effects of LCWJ specimen geometries, initial crack types, and sizes. The comparisons between simulated results and standards analytical solutions were executed, which exhibit good accordance. It proved that the fatigue fracture simulation procedure based on LEFM is appropriate for the fatigue assessment of LCWJs. Eventually, it conducted the parametric analysis by predicted S-N curves, which included in the weld length, initial crack shape, initial crack size, penetration length, and materials fracture parameter, to explore some safety assessment reference lines for both failure modes of LCWJ.

This study investigated the fretting fatigue behavior and mechanism of 35CrMoA steel of different contact stresses under diamond and square loading paths in the form of curved surface contact. The results show that multiple crack sources will initiate on the subsurface of the specimen under the combined effect of contact stress and cyclic stress. Under low contact stress, only one crack source dominates, causing the instantaneous fracture zone to be biased to the other side of the main crack source. Under high contact stress, the crack sources in both fretting zones play a dominant role, making the shape of the instantaneous fracture zone into a nearly circular shape with better symmetry; At the beginning of the fretting fatigue, cracks only propagate in the cross-section where they form. When they propagate to a certain depth, a component that propagates in the longitudinal direction will be generated.

The process of fatigue spalling in the rings of ball bearings at durability exceeding 10 8 cycles under in-service loading conditions is analyzed on the basis of fractography and the slices prepared in radial planes of rings. The cracks are shown to originate at subsurface from carbides inherent in the bearing steel or inclusions permissible by sizes for the material. Subsequently, the development of cracks perpendicular to the ring raceway surface takes place similarly as in the VHCF regime with the elliptical “fish-eye” formation. The subsequent crack growth was demonstrated step-by-step up to the ring material fragment separation. The total crack path by alternating stops of propagation and new crack nucleation under conditions of mixed-mode I+II+III mechanisms with the crack branching was discussed. In the final stage, the crack grows towards the ring raceway and either appears on the raceway surface or coalesce with a similar adjacent crack followed by fatigue spalling formation.

This study aims to develop a high temperature LCF test method using a non-standard miniature thin-plate (MTP) specimen in order to characterize cyclic visco-plasticity behavior of component materials. For demonstration, fully reversed strain-range controlled LCF and creep-fatigue (CF) tests at 600 °C have been performed for a martensitic steel using both standard-sized full-scale (SSFS) and MTP specimens. A scaling factor is determined using cyclic visco-plastic finite element (FE) for geometry constraint evaluation and data conversion based on the reference strain approach. The equivalent energy principal is proposed to assess the geometry constraint effect that non-standard MTP specimen has. The high temperature LCF results from the MTP specimen based on the proposed testing methodology have shown a good agreement with SSFS specimen data under equivalent conditions. The methodology can therefore be used to conduct accurate transferability to achieve equivalent LCF behavior between the conventional standard specimen and the MTP specimen.

In this study, an approach utilizing a conjunction of the extended finite element method (XFEM) and the GTN micro-mechanical damage model is proposed for predicting the ductile crack propagation of a mill-annealed Ti-6Al-4V alloy. The cohesive model based XFEM approach is used to capture the continuous crack propagation process and the GTN model is applied to describe the constitutive behavior of the material. Simulations are conducted by using the standard finite element code ABAQUS following a Newton-Raphson algorithm solution with employing the user material subroutine of the GTN model. In comparison to the experimental results of the smooth, notched and cracked titanium specimens, this approach is shown to be an efficient method for simulating the ductile crack propagation process under different stress triaxialities.

The present study is aimed at validation of notch stress/ strain estimation schemes such as classical Neuber, Hoffmann-Seeger and recently developed Ince-Glinka method for Nuclear piping material (low C-Mn steel). The study has considered different constraints, loading conditions, various hole sizes to accommodate strain gradient variations and equivalent peak strains. The notch stress field evaluated using these schemes is compared with corresponding stress using elastic-plastic Finite Element (FE) analyses. The comparisons have brought out that the Hoffmann-Seeger scheme results in reasonably accurate assessment of stress localization nearly for all constraint geometries, loadings and strain gradients. However, the classical Neuber scheme is more suitable for low constraint geometries and intermediate constraint geometries whereas it results in under-estimation of maximum principal stress for high constraint geometries, thereby leading to over-prediction of fatigue life. Further, the suitability of energy equivalence equations of Ince-Glinka model for individual stress components, has been reviewed.

The present paper investigates the variability in the static and cyclic properties of two nominally identical supplies of the aeronautical Al grade 7075-T6. Samples were extracted from extruded bars of 15 mm and 60 mm diameter and with slightly different chemical composition. Noticeable differences were found in tensile strength, total elongation, low- and high-cycle fatigue strength, despite the nearly identical hardness value. The diverse mechanical behavior has been imputed to different extrusion ratio and therefore work hardening along with a more or less fine distribution of precipitates and dispersoids. The high-cycle fatigue strength was found to be in direct correlation with the monotonic yield strength and the size of the largest intermetallic precipitate. A simple equation based on Murakami sqrt(area) parameter is proposed to predict the fatigue endurance. Tensile tests and microstructural analyses are recommended instead of conventional hardness tests to have a tighter quality control on the mechanical properties of semifinished products.

The present-day interest in the use of composite-steel joints in primary marine applications requires an in-depth knowledge of the fatigue performance of thick adhesive joints. This paper reports on experimental tests, quasi-static and fatigue, performed on unaged and aged bi-material double strap joints with thick adhesive bondlines. The specimens are monitored by Digital Image Correlation and Infrared Thermography techniques to evaluate the types and extent of damage that occur in the joint during fatigue loading. The S-N curve of the aged joint is evaluated along with it's fatigue limit. It is found that the unaged specimens fail due to cohesive damage, hackles and disbond at the adhesive-adherend interface and the aged specimens failed due to delamination within the composite. The specimens that survived fatigue loading showed similar residual strength as specimens that were not fatigue loaded.

Stir zone (SZ) of AA6061-T6 double-side friction stir welding (DS-FSW) joint with a thickness of 6 mm had a poor fatigue performance compared with that of base metal (BM). The rolling process was employed to improve the fatigue performance of SZ. The results showed that rolling process increased the dislocation density in SZ and remarkably enhanced its fatigue performance. The crack initiation played a key role in the fatigue performance of SZ. It relied on the debonding of lamellar structure in SZ. The debonding of lamellar structure depended on the cracking of fine grain layer in lamellar structure.

Abstract: In order to study the dynamic fracture properties of FRP strengthened concrete, the three-point bending experiment with different initial crack-depth ratios was carried out under dynamic loading. The effects of crack-depth ratios on the fracture parameters were analyzed. Combined with Pearson Correlation Coefficient formula, the correlation between crack-depth ratios and fracture parameters was quantitatively verified. The conclusions could be drawn that, there are three critical points in the damage process: the crack initiation point, first peak point and ultimate bearing capacity point. With the increase of crack-depth ratio, the crack initiation load decreases, but the first peak load and ultimate load increase first and then decrease. The stress intensity factors of three points also increase first and then decrease. The increment of critical crack-depth ratio and flexibility coefficient are related to crack-depth ratio, which could reflect the effect of crack-depth ratio on the deformation capacity of FRP strengthened concrete.

This work investigates the influence of temperature on the creep damage behaviors of red sandstone. The samples treated at 25 ℃, 200 ℃, 400 ℃ and 600 ℃ are selected to carry out the uniaxial compression and creep experiments. It is found that temperature has obvious influence on uniaxial compressive strength, Young’s modulus and failure modes of red sandstone. It can be also believed that the temperature can degrade the mechanical behaviors of red sandstone. However, as the temperature increases, the damage value does not always increase, the damage variable has a negative value at 25 ~ 400 ℃. It can be found that the higher the temperature, the larger the effect of loading ratio on the ratio of creep strain to instantaneous strain, that is, temperature reduces the ability of red sandstone to resist creep deformation. Acoustic emission (AE) technology has been also used in the loading process of uniaxial compression and creep tests. It is found that the probability density of AE absolute energy of different samples still satisfies the Gutenberg-Richter law well. In uniaxial compression test, as the temperature increases, the absolute value of the critical index increases exponentially. In the uniaxial creep test, as the loading ratio increases, the absolute value of the critical index first decreases and then increases. When the loading ratio is the same, as the temperature increases, the absolute value of the critical index also increases exponentially.

This paper presents and compares two combined experimental-numerical techniques for the investigation of fracture properties of additively manufactured polymer parts using digital image correlation (DIC) measurements. The first method uses only measured kinematic fields, and the second is based on Finite Element simulations driven by measured boundary conditions. A micro Single Edge Notched Tensile sample manufactured by fused filament fabrication of ABS is studied. It is shown that both methods locally extract J-integrals, and the crack tip is accurately located by the FE-based method. By comparing computed displacements to those measured via DIC it is possible to locally check the validity of the numerical model. The initiation and propagation stages are analyzed independently thanks to two different magnifications of acquired image series

Fatigue cracks initiated from holes in several zones and structural components of the RRJ-95 aircraft frames were investigated. Using the method of quantitative fractography the crack growth duration in the brackets of the in-service airframe and in the wing panels during full-scale bench tests was estimated the spacing of meso-beach-marks (MBM) and fatigue striations. The applied program of bench test consisted of blocks of variable loads that were equivalent to the wing loading in flight and reproducing schematized flight-cycle. It was shown that the duration of fatigue crack propagation in several structural components of the RRJ-95 aircraft frames was approximately the same as for the crack nucleation duration. The total lifetime is sufficiently long for cracks in the structural components to be detected and reliably monitored with a large operating time interval between adjacent inspections.

Due to the additional local stress concentration caused by undercut and misaligned defects, welded joints own less fatigue strength. This work uses probabilistic technique and fracture mechanics theory to quantitatively investigate the impacts of undercuts and misalignments on fatigue performance and reliability of Load-carrying Cruciform Welded Joint (LCWJ). Firstly, the geometrical characteristics summary of the size and type of undercuts and misalignments are provided from researches and experiments. Subsequently. Evaluations of the stress levels are combined with the nominal loadings in LCWJs, probabilistic distributions of material fracture properties, and various configurations of geometries and flaws. Meanwhile, the estimations of fatigue strengths are conducted by the probabilistic reliability theory by taking into account the distributions of the actual fatigue data. The findings reveal a clear disparity between the base metal and weldment test results. Different reliability levels for various defect types and sizes and in LCWJs are caused by the tolerance limits.