Fatigue Crack Propagation Research Articles

Effects of Anisotropic Microstructure and Load Ratio on Fatigue Crack Propagation Rate in Additively Manufactured Ti-6Al-4V Alloy

Additive manufacturing (AM) refers to advanced technologies for building 3D objects by adding material layer upon layer using either electron beam melting (EBM) or selective laser melting. AM allows us to produce lighter and more complex parts. However, various defects are created during the AM process, which severely affect fatigue behavior. In the current research, the effects of the anisotropic microstructure in the in-plane and out-of-plane orientations and defects on the fatigue crack propagation rate (FCPR) and crack path were studied. A resonance machine was used to determine the fatigue crack propagation rate (da/dN vs. ΔK) from the near-threshold up to the final fracture, accompanied by in situ Acoustic Emission (AE) monitoring. Micro-Computerized Tomography (µCT) enabled us to characterize surface and microstructural defects. Metallography was used to determine the microstructure vs. orientations and fractography to classify the fatigue fracture propagation modes. Calculations of the local stress distribution were performed to determine the interactions of the cracks with the defects. In the out-of-plane direction, the material exhibited high fatigue fracture toughness accompanied by a slightly lower fatigue crack propagation rate as compared to in-plane orientations. The near-threshold stress intensity factor was slightly higher in the out-of-plane orientation as compared to that in the in-plane one, accompanied by a lower exponent of the Paris law regime. The threshold decreased with an increasing load ratio as expected for both orientations. The crack propagation direction that crosses the elongated grains plays an important role in increasing fatigue resistance in the out-of-plane direction. In the in-plane directions, the crack propagates parallel to the grain boundary, interacts with more defects and exhibits more brittle striations on the fracture surface, resulting in lower fatigue resistance.

Fatigue Crack Propagation Analysis of Rail Surface Under Mixed Initial Crack Patterns

Prolonged rolling contact fatigue between wheels and rails results in the formation of surface cracks on the rail and accurately analyzing the crack expansion behavior is essential to ensuring the safe operation of the train. Drawing upon the principles of fracture mechanics and finite element theory, this study establishes a finite element model of wheel–rail rolling contact that incorporates the presence of cracks. The method utilizes an interaction integral to calculate the stress intensity factors at the leading edge of the crack; then, the Paris formula is used to solve the crack spreading rate. It systematically examines the effects of the initial crack angle, the coefficient of friction of wheels to rails, and crack size on the behavior of fatigue crack propagation. The results indicate that the cracks primarily extend in the depth direction of the rail, transforming the semi-circular surface cracks into elliptical cracks with the major axis oriented along the rail’s width. Crack propagation is primarily driven by model II and III composite crack propagation, with their expansion rates influenced by operating conditions. In contrast, mode-I expansion is less sensitive to these conditions. Under single-variable loading conditions, a smaller initial crack angle results in a faster crack growth rate. Increasing crack length accelerates crack growth, while a higher friction coefficient inhibits it.

Fatigue Crack Growth Performance of Q370qENH Weathering Bridge Steel and Butt Welds

Weathering steel possesses good atmospheric corrosion resistance and is increasingly applied in highway and railway bridges. The fatigue performance of the weld joint is an important issue in bridge engineering. This study experimentally investigates the microstructural properties and fracture crack growth behaviors of a Q370qENH bridge weathering steel weld joint. The FCG parameters of the base steel, butt weld, and HAZs, considering the effect of different plate thicknesses and stress ratios, are analyzed. Microstructural features, microhardness, and fatigue fracture surfaces are carefully inspected. The FCG rates of different weld regions in the stable crack growth stage are obtained using integral formulas based on the Paris and Walker law. The test results indicate that the heating and cooling process during the welding of Q370qENH steel creates improved microstructures with refined grain sizes and fewer impurities, thus leading to improved FCG performances in the HAZ and weld regions. The crack growth rate of Q370qENH weld regions increases with the stress ratio, and the influencing extent increasingly ranks as the base steel, HAZ, and the weld. The thick plate has a slightly slower fatigue crack growth rate for the Q370qENH weld joints. The Q370qENH base steel presents the highest fatigue crack growth rate, followed by the heat-treated and HAZ cases, while the weld area exhibits the lowest FCG rate. The Paris law coefficients of different regions of Q370qENH welds are presented. The collected data serve as a valuable reference for future analyses of fatigue crack propagation problems of Q370qENH steel bridge joints.

Influence of surface integrity on short crack growth behavior in HFMI-treated welded joints

AbstractThis study investigates the influence of surface integrity and the localized fatigue phenomena on the initiation and propagation of short fatigue cracks in high-frequency mechanical impact (HFMI)-treated welded joints. The treated surface region, characterized by a compressive residual stress field, smooth notch geometry, and work hardening layer, improves welded joints’ fatigue strength. However, how these surface conditions influence the fatigue damage process zone during short crack initiation and growth is not yet well known. Therefore, this study systematically investigates the influence of different surface characteristics on fatigue life modeling of HFMI-treated welded joints made of high-strength steel. This is achieved using a non-local continuum damage mechanics-based approach of crack growth and elastic–plastic finite element simulation, explicitly modeling treated surface conditions. The simulated fatigue life is first verified with experiments and then applied to various surface conditions. The simulation results show that most of the fatigue life is spent until a crack size of 0.2 mm. The compressive residual stress field greatly extends both short crack initiation and propagation life, with its degree of contribution highly dependent on loading history and residual stress change. The role of the work hardening layer is mainly concentrated on improving fatigue life during short crack initiation and the very beginning of short crack growth.

Effective stress intensity factor range for fatigue cracks propagating in mixed mode I-II loading

The actual service axles are often subjected to mixed-mode loading, and predicting the mixed-mode I-II crack propagation behaviour using the mode I effective stress intensity factor (ΔKI) differs from the real service conditions. To effectively predict the fatigue crack propagation behaviour of actual service structures, the I-II stress intensity factor range (ΔKP-R) considering two closure effects was adopted to describe the fatigue crack propagation under mixed mode loading. A test database was established based on monitoring data of mode I and mixed-mode I-II (30/45/60°) crack propagation tests under different stress ratios. Combining domain knowledge and symbolic regression (SR) methods, an angle factor was proposed for constructing correlation functions between ΔKI and ΔKP-R. The results showed that the loading angle (α) only affects the initial projection of the load parallel and perpendicular to the fatigue crack growth (FCG) direction. Compared with the geometric correction factor, the correlation function acquired by the angle factor constructed by the SR method has higher accuracy, and the balance parameters (SCORE) obtained by the former are significantly higher than those obtained by the latter under the same function complexity. The SR verification results demonstrated that constructing mode I and I-II correlation functions with angle factors has a good predictive effect.

Efficient and accurate determination of crack propagation rate without unloading-induced crack closure

The accurate delineation of the fatigue crack growth rate (da/dN) model, encompassing the short crack stage, assumes paramount importance in the operation and maintenance of transportation vehicles such as aircraft. Nonetheless, the determination of the da/dN encounters challenges, notably crack closure engendered by unloading observations on the specimen and the attendant issue of exorbitant test expenditures due to low load amplitude (ΔP), thereby impeding the precise establishment of the da/dN model, particularly in the short crack stage. Hence, this study initially posits a novel crack observation methodology employing a self-engineered stress transfer apparatus to sustain the stress (σ) on the specimen at its closure stress (σcl) level post-unloading, thus mitigating the impact of crack closure on crack observation and augmenting the accuracy of da/dN curve determination. Subsequently, building upon this innovation, a fatigue crack propagation (FCP) test protocol tailored for the short crack stage is advanced, principally by substantially augmenting ΔP to surmount the cost constraints of the test, thereby broadening the scope of da/dN curve determination to 10−8 mm/cycle. Lastly, premised on the acquisition of high precision and comprehensive da/dN curves, a da/dN model is posited by integrating with the extant da/dN model, which can comprehensively and precisely delineate the FCP behavior across the entire crack growth spectrum, particularly in the short crack stage. Illustratively demonstrated through a case study on 42CrMo steel crankshaft, a fatigue life (Nf) prediction investigation conducted based on this da/dN model substantiates its efficacy in accurately assessing the FCP behavior of crankshaft materials vis-à-vis existing models, thereby reducing the Nf prediction error by 14.64 %.

Tibial Baseplate Microstructure Governs High Cycle Fatigue Fracture InVivo.

Previous studies report rare occurrences of tibial baseplate fractures following primary total knee arthroplasty (TKA). However, at a microstructural scale, it remains unclear how fatigue models developed invitro apply to fractures invivo. In this study, we asked: (1) do any clinical factors differentiate fracture patients from a broader revision sample; and (2) invivo, how does microstructure influence fatigue crack propagation? We identified three fractured tibial baseplates from an institutional review board exempt implant retrieval program. Then, for comparison, we collated clinical data from the same database for n = 2120 revision TKA patients with tibial trays. To identify mechanisms, we characterized fracture features using scanning electron and digital optical microscopy. Additionally, we performed cross sectional analysis using focused ion beam milling. The fracture cohort consisted of moderately to very active patients with increased implantation time (15.6 years) compared to the larger revision patient sample (5.1 years, p = 0.009). We did not find a significant difference in patient weight between the two groups (p = 0.98). Macroscopic fracture features aligned well with both previous retrieval analysis and invitro baseplate fatigue tests. On a micron scale, we identified striations on each baseplate, demonstrating fatigue as the fracture mechanism. Invivo fatigue fracture processes depended on both the alloy (Ti-6Al-4V vs. CoCrMo) and the microstructure of the alloy formed during manufacturing. For Ti-6Al-4V, the presence of equiaxed or acicular microstructure influenced the fatigue crack propagation, the latter arising from large prior β grains and a Widmanstatten microstructure, degrading fatigue strength. CoCrMo alloy fatigue cracks propagated linearly, crystallographically influenced by planar slip. However, we did not document any features of overload or fast fracture, suggesting a high cycle, low stress fatigue regime. Ultimately, the crack profiles we present here may provide insight into fatigue fractures of modern tibial baseplates.

Creep-fatigue interactive behavior and damage mechanism of TP321 stainless steel under hybrid-controlled conditions

In this study, Hybrid-controlled creep-fatigue (HCCF) tests were conducted on TP321 austenitic stainless steel under a variety of test conditions. The effects of strain amplitude, holding time, holding stress and temperature on the creep-fatigue behavior of TP321 austenitic stainless steel were not only analyzed in detail but also revealed the creep-fatigue damage interactive mechanism. The results demonstrated that a rise in test temperature and load holding time markedly induced creep deformation, resulting in a notable reduction in failure life. Additionally, an increase in test temperature led to the cessation of the cyclic hardening phenomenon. Secondly, the analysis of fracture morphology and X-ray computed tomography (X-CT) scanning results demonstrated that the transgranular cracks expanded inwards and connected with the intergranular voids under creep-fatigue interaction, forming a mixed intergranular and transcrystalline fracture mode. The presence of large creep cavities impeded the propagation of fatigue cracks when creep damage was the dominant phenomenon. Subsequently, the damage evolution mechanism was elucidated through microstructural analysis, which revealed that the impact of the slip bands on the triangular grain boundaries and the precipitation of carbides facilitated the nucleation of voids and the internal formation of intergranular microcracks, thereby causing creep-fatigue damage interaction. Finally, the TP321 austenitic stainless steel creep-fatigue damage interactive mechanism diagram was proposed in conjunction with the fracture morphological characteristics and microstructure.

In-situ SEM investigation of fatigue crack propagation through cross-weld area in WAAM low-carbon steel and the role of microstructures in propagation behavior

In-situ SEM investigation of fatigue crack propagation through cross-weld area in WAAM low-carbon steel and the role of microstructures in propagation behavior

Influences of the stress ratio and local micro mineral aggregates on small fatigue crack propagation in the shale containing bedding planes

Due to the existence of bedding planes in shale oil reservoirs, the complexity of crack networks created by conventional hydraulic fracturing (HF) technology is limited, resulting in low oil production. In this paper, a fatigue loading method was proposed to increase the complexity of the cracking network. The propagation behaviors of small cracks were investigated and compared under both monotonic and fatigue loading conditions by using SEM in-situ three-point bending tests. In addition, the influences of local micro mineral aggregates and stress ratios (R = 0.1, 0.3 and 0.5) on the propagation behavior of small fatigue cracks (SFCs) in shale were quantitatively evaluated. The SEM in-situ fatigue tests demonstrated the effectiveness of fatigue loading in enabling SFC to propagate through the bedding plane and increase crack network complexity from a micro perspective. A fitting exponential formula of the stress intensity factor range threshold ΔKth and stress ratio R was obtained. This study assists us in deeply understanding the influence of micro mineral aggregates and stress ratio on the SFC propagation mechanism and its implications for HF design in shale oil reservoirs.

Simulation of mixed mode I-II fatigue crack propagation in concrete with different strengths

The mode-I fatigue crack propagation in concrete has been extensively studied. However, many concrete structure failures occur subjected to mixed-mode fatigue loads in practice. The accurate predictions for the mixed mode I-II fatigue crack propagation and fatigue life are crucial for evaluating the structural safety of concrete constructions. In this paper, the mixed mode I-II fatigue crack propagation process on concrete with different strengths is simulated using the fatigue tension-softening constitutive model and the crack propagation criterion of the initial fracture toughness as a parameter (SIF-based criterion). The numerical results indicated that the fatigue crack length decreases with increasing the concrete strength for a given fatigue load level, but the fatigue life significantly increases with concrete strength. Further, a modified Paris law is presented on the basis of the numerical results for concrete with different strengths. With the known tensile strength of concrete, the mixed mode I-II fatigue crack propagation rate of concrete with different strengths can be presented. The proposed model in this study is useful in further predicting the fatigue life of concrete structures under mixed-mode fatigue loads.

Effect of grain boundary phase formed by Mn addition on initiation and propagation of fatigue cracks in homogenized Cu-6Ni-1.3Si alloy

High-strength cast Cu alloys often contain substantial quantities of alloying elements that promote the nucleation of heterogeneous particles, particularly at grain boundaries (GBs). In the Cu-6Ni-1.3Si alloy, intermetallic compounds such as Ni2Si form within the matrix and along the GBs following homogenization. Ni2Si particles within the matrix are homogeneously nucleated with diameters of a few tens of nanometers, which enhances matrix strength. However, heterogeneously nucleated Ni2Si particles at GBs, which can be several micrometers in size, negatively impact overall strength. To improve the strength of Cu-6Ni-1.3Si alloy, 2.1 wt% Mn was added. This Mn addition led to the formation of plate- or film-shaped intermetallic compounds, specifically Ni16Si7Mn6 (G-phase), at GBs after homogenization. Despite the Mn addition, Ni2Si precipitates with diameters of a few tens of nanometers still formed within the grains, but these were more densely distributed in the Mn-added alloy compared to the Mn-free alloy. Fatigue tests conducted on round bar specimens of both alloys showed that Mn addition enhanced fatigue strength. This enhancement is attributed to the suppression of both crack initiation and propagation along the GBs and within the matrix.

Experiments and numerical simulations on fatigue properties of laser shock peening for FV520B steel

Laser shock peening (LSP) experiments, low cycle fatigue experiments, microhardness and residual stress measurements, and scanning electron microscopy (SEM) analyses were conducted on FV520B steel cylindrical specimens. Additionally, ABAQUS software was employed to predict fatigue life following the LSP process. The experimental results indicate that the surface compressive residual stresses induced by LSP inhibit both the initiation and propagation of fatigue cracks effectively, thereby prolonging the fatigue life of FV520B steel. The fatigue life of specimens at strain amplitudes of ± 0.5 %, ±0.6 %, ±0.7 %, and ± 1.0 % is improved by 132.2 %, 0.4 %, 18.0 %, and 88.8 %, respectively. A residual stress of −90 MPa is measured on the surface of the specimen and the surface hardness value increase by 48 % after LSP. The SEM results reveal that the characteristic of single crack sources for crack initiation is presented after LSP. The results of single point LSP simulation using ABAQUS demonstrate that the circumferential surface experiences a lower compressive residual stress of 30 MPa compared to a higher value of 45 MPa on the planar surface, this discrepancy arises due to rapidly decay associated with reduced rebound tensile strain on convex surfaces. A “multi-point continuous shock” simulation strategy was implemented for modeling LSP effects on the circumferential surface. The average compressive residual stress achieved was found to be 92 MPa, additionally, tensile residual stresses ranging from 8 MPa to 29 MPa were detected within secondary surfaces and inside the cylinder. Notably, discrepancies between simulated and experimental fatigue lives for LSP specimens across strain amplitudes of ± 0.5 %, ±0.6 %, ±0.7 %, and ± 1.0 % were minimal-ranging only between 10.4 % and 22.3 %.

Study on Microstructure and Corrosion Fatigue Resistance of 14Cr12Ni3Mo2VN Materials Based on the Composite Technology of High-Frequency Induction Quenching and Laser Shock Peening

This study investigated the microstructure, microhardness, and residual compressive stress of 14Cr12Ni3Mo2VN martensitic stainless steel treated with high-frequency induction quenching (HFIQ) and laser shock peening (LSP). Using rotating bending corrosion fatigue testing, the corrosion fatigue performance was analyzed. Results show that a microstructural gradient formed after HFIQ and LSP: the surface layer consisted of nanocrystals, the subsurface layer of short lath martensite, and the core of thick lath martensite. A hardness gradient was introduced, with surface hardness reaching 524 Hv0.1, 163 Hv0.1 higher than the core hardness. A residual compressive stress field was introduced near the surface, with a maximum residual compressive stress of approximately −575 MPa at a depth of 0.1 mm. Corrosion fatigue results indicate that cycle loading times of samples treated with HFIQ and LSP were 2.88, 2.04, and 1.45 times higher than untreated, HFIQ-only, and LSP-only samples, respectively. Transmission electron microscopy (TEM) characterization showed that HFIQ reduced the lath martensite size, while the ultra-high strain rate induced by LSP likely caused dynamic recrystallization, forming numerous sub-boundaries and refining grains, which increased surface hardness. The plastic strain induced by LSP introduced residual compressive stress, counteracting tensile stress and hindering the initiation and propagation of corrosion fatigue cracks.

Effect of Al Element on Retained Austenite, Residual Compressive Stress, and Contact Fatigue Life of Carburized and Quenched 20MnCr5 Steel Gear

To improve the contact fatigue life of gears, we studied the effect of adding a certain proportion of the Al element to a 20MnCr5 steel FZG spur gear under different heat treatment processes, characterizing the retained austenite and residual compressive stress on the tooth surface. The stability of the microstructure grain size on the gear surface under different heat treatment processes was studied, and the surface microstructure, phase structure, and composition of the gear were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The changes in the retained austenite content and grain size on the gear surface at a microscale of 2–100 μm were investigated. In addition, this study revealed the effect of adding the Al element and the optimization of the carburizing and quenching process on the residual compressive stress on the gear surface at a depth range of 200–280 μm. The effect of higher residual compressive stress and fewer non-metallic inclusions on the gear surface on the stress intensity factor of fatigue crack propagation was considered, along with the effect of deeper hardened layers on the improvement in wear resistance. The experiments in this study significantly improved the contact fatigue life of 20MnCr5 steel gears.

Prediction of fatigue crack propagation behavior in elastic plastic region under block loading for type 316 steel via artificial neural network approach

This study investigated the fatigue crack propagation behavior from small defect in the elastic–plastic region under block loading conditions and clarified the influence of cycle ratio on the crack growth rate. Fatigue tests were conducted under constant and repeated two-step strain amplitude loading conditions using various cycle ratios. The results of the constant amplitude loading test indicated that the J integral can be employed to predict fatigue crack propagation rate in one master curve by considering the material constant, l0. The results of the repeated two-step test showed that the fatigue life evaluated via the J integral had a larger scatter for test conditions at strain amplitudes of 1.0%/0.2% and 0.8%/0.2% with various cycle ratios. A highly accurate model was established to predict fatigue crack propagation behavior and investigate the effect of algorithms on the precision of models. To achieve this, three deep learning algorithms feed forward neural network (FFNN), cascade-forward neural network (CFNN) and function fitting neural network (FNN), were employed. It was observed that the precision of the constructed models was dependent on the algorithms and dataset split. The model constructed using the CFNN exhibited the highest prediction accuracy.

Fatigue cracking propagation behavior of 10CrNi3MoV steel mismatched welded joints at sub-temperature

This paper investigates fatigue crack propagation behavior of high-strength steel 10CrNi3MoV and its mismatched weldments under low-ambient temperature conditions. The BM and its weldments under four temperatures (T = 20 °C, −20 °C, −40 °C, −60 °C) were tested to quantify Fatigue Crack Growth Rate (FCGR) by specific fatigue tests using two stress ratios (R = 0.1, 0.6) conditions. The findings indicate that an increased stress ratio leads to a higher mean stress, potentially accelerating the FCGR under identical loading conditions. The reduced temperature may elicit advantageous impacts on FCGR behavior for the examined materials. Moreover, the undermatched weldments generally exhibited a lower FCG resistance for 10CrNi3MoV steel under low temperature conditions. The critical temperature point of Fatigue Ductile-to-Brittle Transition (TFDBT) is deduced from the quantitative competitive relationship between the fatigue resistance and embrittlement. FCGR for these materials would be reaccelerated when temperature is lower than TFDBT. Finally, the fitted constants C and m in Paris law were determined to reveal that the TFDBT of studied materials reaches around −40 °C.

Advancing the understanding of short fatigue crack propagation: Leveraging ultrasonic testing device to approach rolling contact fatigue

This paper uses ultrasonic testing devices to approach the rolling contact fatigue (RCF) stress state experienced during rolling on an indented surface, in order to understand the primary cause of failures of rolling element bearings in aeronautics. It relies on testing specimens made of M50-VIM/VAR steel while inducing compressive preload. This leads to a localized multi-axial and non-proportional stress field, induced by an artificial surface defect created via electro-discharge machining (EDM). Observations reveal that the surface crack initiation occurs along the EDM beyond 108 cycles, with no shift observed from surface defects to sub-surface defects, as commonly seen in very high cycle fatigue (VHCF) regime. Our analysis suggests that the stress intensity factor range, ΔK, may govern surface initiation in the VHCF regime, particularly when the formation of fine granular area (FGA) is not feasible. Consequently, under fixed stress conditions, there exists a critical surface defect size below which short crack initiation becomes improbable. These results mirror the behavior usually observed for indentations and thereby connect ultrasonic loading with RCF. Besides, initiations of fatigue butterfly and FGA appear to be associated with VHCF tests, compression, high levels of multi-axial stresses, and the refinement of microstructure at low temperatures. These findings shed light on a potential link between fatigue butterfly and FGAs, attributed to the same underlying cause: cross-slip.

Revealing the influence of initial δ phase on high-temperature low-cycle fatigue behavior of GH4169 superalloy

In this study, GH4169 superalloy with varying initial δ phases was obtained through different annealing treatments. Cyclic stress–controlled low cycle fatigue (LCF) experiments were carried out at 650 °C to examine the influences of the initial δ phase content and morphology on LCF behavior. The results revealed that LCF life increased with prolonged annealing time, peaking at 7 h. However, beyond 8 h, a significant decrease in fatigue life occurred, followed by a slight increase with further extension of annealing time. The morphology and distribution of the δ phase played a crucial role in fatigue crack growth. The short rod-like δ phase effectively impeded crack propagation, contributing to an extended LCF life. Conversely, when the needle-like δ phase aligned with the crack growth direction, the crack growth rate increased, reducing LCF life. However, when the needle-like δ phase was oriented perpendicular to the crack growth direction, it obstructed fatigue crack propagation, thereby delaying fatigue fracture. Overall, annealing for 7 h provided the optimal LCF life at 650 °C.

Sequential irradiation does not improve fatigue crack propagation resistance of human cortical bone at 15 kGy

Sequential irradiation has been advocated for mitigating the reduction in fatigue properties of tendon compared to a single dose. However, to our knowledge, its capability of mitigating fatigue losses in bone is unknown. Recently, we reported that sequential irradiation did not mitigate losses in high-cycle S-N fatigue life of cortical bone at 15 kGy; however, it is unclear if sequential irradiation provides a benefit to fatigue crack propagation resistance. Our previous study also showed that radiation-induced collagen chain fragmentation and crosslinking increased from 0 to 15 kGy, suggesting that both likely contribute to the reduction in high-cycle S-N fatigue life within this dose range. Our objectives were: 1) to evaluate the fatigue crack propagation resistance of cortical bone and the effect of radiation on fracture plane damage zone thickness (DZT) at the crack tip in the dose range of 0–15 kGy, and 2) to evaluate whether sequential irradiation at 15 kGy mitigates the loss of fatigue crack propagation resistance of cortical bone compared to a single irradiation dose. Compact tension specimens from four male donor femoral pairs (ages 21–61 years old) were divided into 5 treatment groups (0 kGy, 5 kGy, 10 kGy, 15 kGy, and a 15 kGy sequential irradiation dose of 5 kGy sequentially irradiated with 10 kGy) and subjected to fatigue crack propagation testing (n = 3–4 specimens per group) where fatigue crack growth rate da/dN and cyclic stress intensity factor ΔK were determined. Following testing, specimens were bulk stained in basic fuchsin, embedded in poly(methylmethacrylate), sectioned, and mounted on acrylic slides to evaluate fracture plane DZT at known crack lengths. Sections were then imaged with a fluorescence microscope, and fracture plane DZT was measured using ImageJ (n = 3–4 specimens per group) and analyzed as a function of ΔK. We observed a decrease in fatigue crack propagation resistance at 15 kGy compared to doses of 10 kGy or lower (p ≤ 0.013). Fracture plane DZT decreased overall with increasing radiation dose from 0 to 15 kGy. Sequential irradiation offered no improvement in fatigue crack propagation resistance (p = 0.98). Radiation-induced collagen chain fragmentation and crosslinking in this dose range likely contribute to a decrease in energy dissipation capability with increasing radiation dose. Other alternative radiation sterilization methods besides sequential irradiation may be warranted to mitigate radiation-induced tissue damage and extend the functional lifetime of structural cortical bone allografts.