Notch Effect Research Articles

Analysis of the uniaxial fatigue behaviour of 42CrMo4 Q&T steel specimens extracted from the big end of a marine engine connecting rod using the heat dissipation approach

Analysis of the uniaxial fatigue behaviour of 42CrMo4 Q&T steel specimens extracted from the big end of a marine engine connecting rod using the heat dissipation approach

Application of adhesively bonded CFRP for reinforcement and rehabilitation of fatigue damaged steel structure - only a nice idea?

As an alternative to classic repair measures of fatigue-damaged steel structures, adhesively bonded CFRP lamellas are ideal. In this way, disadvantages of the established methods can be circumvented Compared to bolted reinforcing measures, cross-sectional weakening by the bolt is avoided. Heat-induced residual stresses and distortions, as they usually occur during repair welding, can also be excluded. These disadvantages represent a weak point during cyclic loading due to the notch effect. To characterize the materials, tests are carried out on small scale specimens. With the help of tests on CT-samples a comparison with established methods such as drilling the crack tip and repair welding is realized. Based on the crack propagation, the great potential of bonded CFRP reinforcements can be deduced. By prestressing the lamellas, the remaining lifetime can generally be further increased. It should be noted, however, that with single-sided prestressing, a precamber of the specimen and, during loading, a secondary bending moment may occur. The combination of bonded CFRP with established methods can be described as particularly effective. With a reinforcement on both sides with pre-stressed plates, up to 7.9 times the remaining service life can be determined in comparison to unreinforced specimens. The effectiveness of adhesively bonded CFRP lamellas is examined in a German research project. Selected results are presented in this paper.

Notch sensitivity of C/C-SiC composite evaluated by flexural tests

The notch effects on the mechanical behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (C/C-SiC) was studied. The in-plane (IP) and out-of-plane (OP) flexural properties of notched and unnotched samples with fiber orientations (0°, 45° and 60°) were determined through 3-point-bending (3PB) and single notched beam (SENB) tests. Despite the significant difference in bending modulus, the strength depends only slightly on the fiber orientation and loading direction, which could be explained through the uneven distribution of SiC-matrix within the block-like structure of C/C-SiC. This unique micro-structure also leads to a relatively constant value of notch sensitivity in the IP direction, and the sensitivity to the notch is relatively low for all tested C/C-SiC specimen configurations. Furthermore, due to the large differences of fracture mechanism, the work of fracture (WOF) in the IP direction is significantly smaller than in the OP direction for all fiber orientations.

Experimental study of the impact of notches and holes made in the front edge of adherends on the properties of static and fatigue strength of adhesive joints

The paper presents the results of experimental studies aimed at determining the effect of holes and notches at the front edge of adherends on the strength of adhesive joints. Single-lap joints made of S235JR steel sheets joined with Araldite 2014-2 epoxy adhesive were tested. Comparative tests of static strength in the shear test as well as high-cycle fatigue strength tests were carried out. Joints with three holes with a diameter of 3 mm filled with adhesive and notches 3 mm wide and 4 mm long also filled with adhesive were tested and compared with reference joints, i.e. without modification. The assumption was that the structural changes applied were to contribute to the reduction of the peak of peel and shear stresses that typically occur in this type of joint. Based on the static strength tests, no significant effect of the applied modifications on the strength of the connections was demonstrated. However, in the case of fatigue strength, a significant improvement in fatigue lifetime was demonstrated, which in the area of low cycle fatigue increased by 328.6 % for the joint with notches and by 640.8 % for the variant with holes. For the fatigue fracture surfaces, a topography analysis was carried out by determining the roughness parameters. Significant differences were exposed since at the leading edge, the selected parameters were significantly lower for the reference variant than for variants with notches and holes.

Effect of notch and stress ratio on Very High Cycle Fatigue characteristics of the carburized 17CrNi high-strength steel and life prediction

In order to investigate the notch effect on the structural characteristics of the carburized 17CrNi high-strength steel in the very high cycle fatigue (VHCF) loading, the axial tests with the stress ratio (R) of ‒1 were performed and the S-N characteristics were studied. The microscopic observation revealed that surface induced failure was the only failure mode. Further, the effect of the notch was investigated: Based on the small crack theory, the calculation of the fatigue notch factor (Kf) was performed and has shown that Kf is slightly less than the theoretical stress concentration factor (Kt). Then, Kf was used to study both the notch effect and stress ratio effect on fatigue life. Finally, the life prediction model associated with R and Kf was established and the calculation results are valid according to the good agreement with the experimental data.

Notch effect identification and fatigue life prediction of undercut weld

Undercut, as a typical surface imperfection at the weld toe, significantly impacts the weld fatigue life. Neither the ISO5817 standard for imperfection level definition nor the traditional fatigue life prediction methods for welds can accurately identify the undercut effect on weld fatigue life. To solve this problem, a new stress concept and life prediction method are proposed, which can predict the fatigue life of undercut welds in both linear elastic and elastic–plastic conditions. Its prediction accuracy is verified by test data and engineering examples.

Numerical Determination of Target Values and Process Parameters of Case Hardening, Taking into Account the Local Stress State of Failure-Relevant Construction Details

Abstract Through the thermochemical process of case hardening, the local material strength of steel components can be increased. In addition to the increase in stress due to the notch effect, the shape of construction details also has an effect on key component properties after case hardening, such as edge hardness and case hardening depth. The component-related specification of target values for case hardening is currently based on empirical values or expert knowledge. In addition, the effect of design details during case hardening is not taken into account when specifying process parameters in the control and regulation software of case hardening systems. This article presents a concept for the numerical determination of target values and process parameters for case hardening based on the stress state of the component. Compared to the empirically based determination of target values and process parameters for case hardening, the application of the concept makes it possible to adapt the case hardening of components to their stress in the failure range and thus significantly increase the energy and resource efficiency of case hardening.

A detailed study of short fatigue crack directions for carbon steel specimens with circular holes subject to cyclic biaxial loads

The effect of notches and biaxial fatigue loading on the crack paths was studied in detail for thin-walled tube specimens with a passing-through hole, paying special attention to the short-crack period. The study was focused on the high cycle fatigue regime. The material was a carbon steel and the tests were under load control, at Rσ=−1. The crack initiation point on the notch surface and the crack direction were studied with an optical microscope on the specimen outer surface and with a scanning electron microscope and a non-contact 3D optical profilometer on the fracture surface. The crack direction was analyzed for several crack lengths, ranging from the length of one average grain to the length of twenty average grains, all lengths within the short-crack regime, in order to carefully observe the evolution of the crack direction in the Stage I and during the transition from Stage I to Stage II. A statistical analysis of the crack initiation point and the experimental crack directions was carried out. In general, the crack initiation point was close to the maximum principal stress point. The crack direction during the first grains was approximately the Mode I direction. There was no initiation in Mode II. The crack continued in the Mode I direction as it got longer, within the short-crack period. The experimental fatigue limits were compared with the predictions calculated with two models from the literature. The direction of the straight lines used by the models to make the predictions were compared with the average crack directions measured experimentally. The goodness of the models, not only from the point of view of the fatigue limit value prediction but also from the closeness of the direction of the line used for the prediction to the experimental crack direction, was discussed.

On the fatigue properties of material extrusion 3D-printed biodegradable composites reinforced with continuous flax fibers

Nowadays, additive manufacturing is increasingly used for prototypes and low-volume products. Firstly, it offers great design freedom; however, the components must inevitably have certain design artifacts that cause stress concentrations. To this end, composites of biodegradable PLA (polylactic acid) matrix and continuous flax fibers were fabricated in this study using material extrusion 3D printing. Static characterization and mechanical fatigue tests between 103 and 2·106 load cycles were performed for plain specimens, three types of notches for the matrix, and two composite configurations. The notches only slightly affected the static performance of the tested materials. Accordingly, compared to the unnotched versions, the PLA matrix and composites exhibited a reduction in tensile strength of up to 8% and 19%, respectively. It was found that compared to the PLA matrix, the fatigue strength at high cycles increased by 1.8 and 2.3 times for the plain composite with a fiber volume fraction of 7.8% and 14% fibers, respectively. In the fatigue of notched composites, the notch effect is reduced by fibers in the tip. The fatigue strength is up to 1.9 and 2.9 times higher compared to the notched matrix for the composite with a smaller and larger volume fraction, respectively.

Corrosion Fatigue of Standard Duplex Stainless Steel X2CrNiMoN22-5-3 under Rotation Bending Load in Northern German Basin Environment

Standard duplex stainless steel X2CrNiMoN22-5-3 is resistant to both, corrosion and mechanical stress, but corrosion fatigue (CF) lowers the lifetime expectancy in a geothermal environment such as the Northern German Basin. Laboratory experiments used the in-situ electrolyte at 369 K in a specifically designed corrosion chamber applying rotation bending cyclic load to failure. CF behaviour was compared to pure push-pull load. Corrosion kinetics are independent of the load applied. Failure is initiated by pits resulting in mechanical degradation. Increased thickness of the passivating layer surrounding pits enhances degradation or delamination. Also, sharp notches located along the pit edge increase notch effects and stress concentration consequently leading to fast crack propagation and early failure.

Notch effect in very high-cycle fatigue behaviour of a structural steel

The presence of a notch or a detail which leads to stress concentration due to complex geometries has a considerable impact on the fatigue life of engineering structures. Therefore, on the one hand, the notch effect must be investigated and considered in the fatigue assessment of these structures. On the other hand, in the last decades, an interest in studying the very high-cycle fatigue regime (VHCF) has been perceived, due to the extension of the service life of engineering components beyond the 10 million cycles. Thus, the notch effect in the VHCF regime was analysed for the S690 structural steel. Therefore, an analytical approach to design notch specimens was developed and a numerical simulation was performed to assess it. Then, an experimental campaign with smooth and notched specimens with two different stress concentration factors was performed in an ultrasonic fatigue machine to assess the VHCF behaviour. The mechanisms of failure and fracture surfaces were also investigated. It was observed a fully notch sensitivity as well as the dominance of surface crack initiation for the S690 steel in the VHCF regime.

Probabilistic fatigue evaluation of notched specimens considering size effect under multiaxial loading

Fatigue evaluation of notch components is key to ensuring the structural integrity of grand equipment and implementing fatigue resistant design, while fatigue models that effectively couple multiaxial stress condition, notch and size effects are still lacking. Accordingly, a new probabilistic fatigue model by combining the weakest link theory with critical plane theory is proposed in this work. Firstly, the critical plane location is determined by calculating the stationary point of the relevant strain energy density function. Then, a new effective stress concept is proposed to establish the connection between experimental data of smooth specimens and equivalent stress in the critical damage region of notched specimens. Meanwhile, a critical damage region considering the size effect is defined to determine the effective stress. Finally, the experimental data of EN8 medium carbon steel and Q345 alloy steel are used for model validation and comparison and the results show that the model has a higher accuracy than the other four models. Additionally, the curves P−σeff‾−Nf can effectively describe the fatigue life scatter.

Knockdown of Notch Suppresses Epithelial-mesenchymal Transition and Induces Angiogenesis in Oral Submucous Fibrosis by Regulating TGF-β1.

Oral submucous fibrosis (OSF) is a chronic disorder with a high malignant transformation rate. Epithelial-mesenchymal transition (EMT) and angiogenesis are key events in OSF. The Notch signaling plays an essential role in the pathogenesis of various fibrotic diseases, including OSF. Our study aimed to explore the effects of Notch on the EMT and angiogenesis processes during the development of OSF. The expression of Notch in OSF tissues versus normal buccal mucosa samples was compared. Arecoline was used to induce myofibroblast transdifferentiation of buccal mucosal fibroblasts (BMFs). Short hairpin RNA technique was used to knockdown Notch in BMFs. Pirfenidone and SRI-011381 were used to inhibit and activate the TGF-β1 signaling pathway in BMFs, respectively. The expression of Notch was markedly upregulated in OSF tissues and fibrotic BMFs. Knockdown of Notch significantly decreased the viability and promoted apoptosis in BMFs subjected to arecoline stimulation. Downregulation of Notch also significantly suppressed the EMT process, as shown by the reduction of N-cadherin and vimentin with concomitant upregulation of E-cadherin. In addition, knockdown of Notch upregulated VEGF and enhanced the angiogenic activity of fBMFs. Moreover, inhibition of TGF-β1 suppressed viability and EMT, promoted apoptosis, and induced angiogenesis of fBMFs, while activation of TGF-β1 significantly diminished the effects of Notch knockdown on fBMFs. Knockdown of Notch suppressed EMT and induced angiogenesis in OSF by regulating TGF-β1, suggesting that the Notch-TGF-β1 pathway may serve as a therapeutic intervention target for OSF.

Numerical and experimental analysis of the notch effect on fatigue behavior of polymethylmethacrylate metal based on strain energy density method and the extended finite element method

Abstract This work investigates the effect of the notch on fatigue behavior by combining two methods: the extended finite element method (XFEM) and the averaged strain energy density (ASED) method, which considers the combined action of bending and shear loading. The ASED method has already been proven accurate for assessing the failure of components in the presence of sharp and blunt notches, and several results are available in the literature for different materials. These results were compared with those obtained from the experimental tests reported here. The main purpose of this study was twofold: The first part is an experimental study of fatigue in rotary bending of specimens weakened by U and V notches made of polymethyl-methacrylate (PMMA) material. Two values for the radius were used for the U-notches (0.2 and 2 mm) and two angles for the V-notches (20° and 140°). The second part of the study consisted of performing several simulation tests using the Cast3m software for different angles and radii. The local approach based on the mean value of the ASED acted over a finite-sized volume surrounding the highly stressed regions. The maximum principal stress located at the notch edge defined the center of the control volume. If the notch is blunt, the control volume assumes a crescent shape with its width measured along the notch bisector line. When the notch is considered pointed (V-notched) or is a crack, the control volume becomes a circle with its center at the notch tip. The presence of geometric discontinuities in structures affects their lifetime by reducing it, producing a high concentration of local energy around the notch tip. Good convergence was obtained between the numerical simulation and experimental results for the ASED in a finished zone surrounding the notch tip.

Effects of Slit Edge Notches on Mechanical Properties of 3D-Printed PA12 Nylon Kirigami Specimens.

Kirigami structures, a Japanese paper-cutting art form, has been widely adopted in engineering design, including robotics, biomedicine, energy harvesting, and sensing. This study investigated the effects of slit edge notches on the mechanical properties, particularly the tensile stiffness, of 3D-printed PA12 nylon kirigami specimens. Thirty-five samples were designed with various notch sizes and shapes and printed using a commercial 3D printer with multi-jet fusion (MJF) technique. Finite element analysis (FEA) was employed to determine the mechanical properties of the samples computationally. The results showed that the stiffness of the kirigami samples is positively correlated with the number of edges in the notch shape and quadratically negatively correlated with the notch area of the samples. The mathematical relationship between the stretching tensile stiffness of the samples and their notch area was established and explained from an energy perspective. The relationship established in this study can help fine-tune the stiffness of kirigami-inspired structures without altering the primary parameters of kirigami samples. With the rapid fabrication method (e.g., 3D printing technique), the kirigami samples with suitable mechanical properties can be potentially applied to planar springs for hinge structures or energy-absorbing/harvesting structures. These findings will provide valuable insights into the development and optimization of kirigami-inspired structures for various applications in the future.

Contribution of overload-induced residual stress to fatigue retardation pertinent to notch geometry

Incorporating tensile overload (OL) or notch to a fatigue-cracked specimen could prolong fatigue life, but the combined effect of both is unclear up to now. To clarify combined effect of OL-induced residual stress (RS) and notch geometry on subsequent fatigue crack growth (FCG), fatigue tests are carried out by a combination of OL conditions, notch geometries and stress-intensity values. After incorporating notch into a post-OL specimen, the results show that fatigue retardation only results from notch effect at early fatigue phase and then from OL-induced RS later. Additionally, the magnitude of FCG-rate changing and crack-propagation length influenced by notch are related to notch geometry and applied stress ratio, respectively.

Notch signaling drives intestinal graft-versus-host disease in mice and nonhuman primates.

Notch signaling promotes T cell pathogenicity and graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (allo-HCT) in mice, with a dominant role for the Delta-like Notch ligand DLL4. To assess whether Notch's effects are evolutionarily conserved and to identify the mechanisms of Notch signaling inhibition, we studied antibody-mediated DLL4 blockade in a nonhuman primate (NHP) model similar to human allo-HCT. Short-term DLL4 blockade improved posttransplant survival with durable protection from gastrointestinal GVHD in particular. Unlike prior immunosuppressive strategies tested in the NHP GVHD model, anti-DLL4 interfered with a T cell transcriptional program associated with intestinal infiltration. In cross-species investigations, Notch inhibition decreased surface abundance of the gut-homing integrin α4β7 in conventional T cells while preserving α4β7 in regulatory T cells, with findings suggesting increased β1 competition for α4 binding in conventional T cells. Secondary lymphoid organ fibroblastic reticular cells emerged as the critical cellular source of Delta-like Notch ligands for Notch-mediated up-regulation of α4β7 integrin in T cells after allo-HCT. Together, DLL4-Notch blockade decreased effector T cell infiltration into the gut, with increased regulatory to conventional T cell ratios early after allo-HCT. Our results identify a conserved, biologically unique, and targetable role of DLL4-Notch signaling in intestinal GVHD.

Fatigue life prediction of notched components under size effect using strain energy reformulated critical distance theory

Notch and size effects show significant impact on the fatigue performance of engineering components, which deserves special attention. In this work, strain energy reformulated critical distance theory was developed for fatigue life prediction of notched components under size effect. Experimental data of different notched specimens manufactured from GH4169, TC4, TC11 alloys and low carbon steel En3B were used for model validation and comparison. Results indicate the proposed model works better than the Yang’s and the Shen’s models.

ELECTROCHEMICAL DAMAGE OF THE TRUNNION IN ACETABULAR REVISION HIP SURGERY

Fracture of contemporary femoral stems is a rare occurrence. Earlier THR stems failed due to design issues or post manufacturing heat treatments that weakened the core metal. Our group identified and analyzed 4 contemporary fractured femoral stems after revision surgery in which electrochemical welds contributed to the failure.All four stems were proximally porous coated titanium alloy components. All failures occurred in the neck region post revision surgery in an acetabular cup exchange. All were men and obese. The fractures occurred at an average of 3.6 years post THR redo (range, 1.0–6.5 years) and 8.3 years post index surgery (range, 5.5–12.0 years). To demonstrate the effect of electrocautery on retained femoral stems following revision surgery, we applied intermittent electrosurgical currents at three intensities (30, 60, 90 watts) to the polished neck surface of a titanium alloy stem under dry conditions.At all power settings, visible discoloration and damage to the polished neck surface was observed. The localized patterns and altered metal surface features exhibited were like the electrosurgically-induced damage priorly reported.The neck regions of all components studied displayed extensive mechanical and/or electrocautery damage in the area of fracture initiation. The use of mechanical instruments and electrocautery was documented to remove tissues in all 4 cases.The combination of mechanical and electrocautery damage to the femoral neck and stem served as an initiation point and stress riser for subsequent fractures. The electrocautery and mechanical damage across the fracture site observed occurred iatrogenically during revision surgery. The notch effect, particularly in titanium alloys, due to mechanical and/or electrocautery damage, further reduced the fatigue strength at the fractured femoral necks. While electrocautery and mechanical dissection is often required during revision THA, these failures highlight the need for caution during this step of the procedure in cases where the femoral stem is retained.

Effect of notch on fatigue performance of marine shaft made of 34CrNi3Mo alloy steel under torsional loading

Joint of flange on a marine shaft subjected to torsional loading was more prone to occur fatigue fracture than the other section on the shaft due to stress concentration effect, so torsional fatigue performance in the vicinity of the joint should be payed more attention in terms of safe navigation of ships. The fatigue analysis of 34CrNi3Mo steel as a novel alloy material with a stress concentration factor of 1.45 under cyclic torsional loads was carried out based on the median S-N experimental method by simplifying the flange and shaft joint into 34CrNi3Mo specimens with u-notch subjected to torsional fatigue loading. The S-N curve and fatigue life of 34CrNi3Mo alloy steel were numerically calculated and compared with experimental fatigue life and the plotted S-N curve. It was found that fitting equation of the S-N curve was close to experimental results. Then, the fatigue performance of 34CrNi3Mo specimens with v-notch at angles of 45°, 90° and 135° was compared by means of the validated numerical method. The fracture macrographs and micrographs of the 14 specimens also were provided to explore the effect of notch on fatigue performance of the 34CrNi3Mo materials and to exploit the failure mechanism of fracture.