Crack Initiation Fracture Toughness Research Articles

On the Cover: Effect of Loading Rate on Mode-I Crack Initiation Fracture Toughness of a NdFeB Rare Earth Permanent Magnet by B. Song, B. Sanborn, T. Martinez, D. Landry, C. Loeffler, R. Ferrizz, J. L. Pacheco

On the Cover: Effect of Loading Rate on Mode-I Crack Initiation Fracture Toughness of a NdFeB Rare Earth Permanent Magnet by B. Song, B. Sanborn, T. Martinez, D. Landry, C. Loeffler, R. Ferrizz, J. L. Pacheco

Tunable architectures in Al/Al2O3 composites for enhanced damage tolerance using zirconium acetate-mediated ice-templating

Achieving lightweight, robust, and resilient materials is a sought-after goal, yet concurrently achieving these attributes presents a substantial challenge. A biomimetic design approach opens doors to innovative possibilities in this domain. In this paper, we use the ice-shaping properties of zirconium acetate (ZRA) to obtain Al/Al2O3 composites with tunable architectures through freeze casting and pressure infiltration. The concentration of ZRA in the initial slurry is critical in controlling the final structure of the composites. The composites’ bending strength, compressive strength, and crack-initiation fracture toughness KIc improve with increasing ZRA concentration in the initial slurry. Interestingly, the crack-extension fracture toughness KJc demonstrates an initial decrease followed by subsequent improvement. In addition, the relationship between cracking mode and structural features in the composites is elucidated to explain the underlying strengthening and toughening mechanisms. This tunable and scale-able ice-templating and manufacturing approach opens new doors for developing high-performance metal-ceramic composites.

Application of modified fracture criteria incorporating T-stress for various cracked specimens under mixed mode I-II loading

Accurate assessment of fracture behavior and life prediction of cracked materials based on the mixed mode fracture criteria is of utmost importance in fracture mechanics. In this study, the modified fracture criteria incorporating T-stress for mixed mode I-II cracks were comprehensively reviewed. Additionally, a comparative analysis was conducted between the experimental results obtained from five different cracked configurations and the theoretical predictions according to these modified criteria. Moreover, a brief discussion was held regarding the effect of T-stress on both crack initiation angle and fracture toughness, accompanied by providing some suggestions. The results revealed that the predictive accuracy of modified criteria exhibited noticeable variations across different cracked configurations due to the significant disparities in both the sign and magnitude of T-stress around the crack tip. However, it was observed that the predicted curves based on the modified fracture criteria for the semi-circular bend and edge-crack triangular specimens had remarkable similarities owing to their similar biaxial stress ratio B. When the mode II loading dominated, the generalized maximum tangential stress, generalized minimum strain energy density and generalized averaged strain energy density criteria were suitable for the semi-circular bend, edge-crack triangular, central crack rectangular and short bend beam specimens with positive T-stresses, whereas the maximum tangential strain, generalized maximum tangential stress and generalized maximum tangential strain energy density criteria could provide better theoretical predictions for central cracked Brazilian disk specimens having a negative T-stress.

Fracture behaviors of modified 9Cr-1Mo steels in liquid lead–bismuth eutectic immersion environment using in-situ testing technique

The 9Cr-1Mo ferrite/martensite steel stands as a crucial candidate material for structural use in lead-cooled fast reactors. However, its susceptibility to embrittlement in liquid lead–bismuth eutectic (LBE) alloy represents a significant hurdle that hinders its widespread application. In this paper, two modified 9Cr-1Mo steels, designated as A-type steel and B-type steel, were proposed by adding aluminum and silicon elements, respectively. To examine the embrittlement caused by liquid LBE the uniaxial tensile tests were conducted on the original T91 steel, A-type steel, and B-type steel in liquid LBE at temperatures of 180 °C, 350 °C and 450 °C. Then, based on the proposed in-situ testing method and compliance method, the fracture properties (J-R curves and the crack initiation fracture toughness) of the above 9Cr-1Mo steels were analyzed at different temperatures. Results showed that the yield stress, tensile strength, and elongation of the modified 9Cr-1Mo steels are higher than those of the original T91 steel, but the A-type steel and B-type steel exhibit different mechanical responses with temperature changes. Moreover, with the increase of temperature, the fracture toughness of T91 steel and B-type steel significantly decreases, but the A-type steel decreases first and then increases. There is no doubt that the crack initiation fracture toughness of the modified 9Cr-1Mo steels is higher than that of the original T91 steel in all tested temperature ranges. Finally, combined with fractographic analysis, the effects of liquid LBE at various temperatures on the embrittlement mechanism of 9Cr-1Mo steels were discussed.

Mechanism and Method of Testing Fracture Toughness and Impact Absorbed Energy of Ductile Metals by Spherical Indentation Tests

To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining the quasi-static fracture toughness and impact absorbed energy of ductile metals from spherical indentation tests (SITs). The stress status and damage mechanism of SIT, mode I fracture, Charpy impact tests, and related tests were first investigated through finite element (FE) calculations and scanning electron microscopy (SEM) observations, respectively. It was found that the damage mechanism of SITs is different from that of mode I fractures, while mode I fractures and Charpy impact tests share the same damage mechanism. Considering the difference between SIT and mode I fractures, uniaxial tension and pure shear were introduced to correlate SIT with mode I fractures. Based on this, the widely used critical indentation energy (CIE) model for fracture toughness determination using SITs was modified. The quasi-static fracture toughness determined from the modified CIE model was used to evaluate the impact absorbed energy using the dynamic fracture toughness and energy for crack initiation. The effectiveness of the newly proposed method was verified through experiments on four types of steels: Q345R, SA508-3, 18MnMoNbR, and S30408.

On the strength and fracture toughness of an additive manufactured CrCoNi medium-entropy alloy

An additively manufactured (nominally equiatomic) CrCoNi alloy was processed by laser powder bed fusion (LPBF). At ambient temperatures (298 K), this medium-entropy alloy displayed a yield strength, σy of ∼691 ± 9 MPa, and an ultimate tensile strength, σu of ∼926 ± 15.2 MPa; at cryogenic temperatures (77 K), yield and tensile strengths increased respectively to σy ∼ 944 ± 6 MPa and σu ∼ 1382 ± 11 MPa. These strength levels are 57 and 44% higher than that of the wrought alloy, due to strengthening from the solidification cellular structures intertwined with dislocations in the LPBF CrCoNi. The crack-initiation fracture toughness, KJIc was measured to be ∼183.7 ± 28 MPa√m at 298 K; this value marginally decreased by ∼4% to ∼176 ± 11 MPa√m at 77 K. These KJIc values of the LPBF CrCoNi were 11% and 35% lower than the wrought CrCoNi alloy at 298 K and 77 K, respectively. The resistance to crack growth of the LPBF CrCoNi from its hierarchical micro- and meso‑structures was evaluated using nonlinear-elastic fracture mechanics by measuring R-curve behavior in the form of the J-integral as a function of crack extension. The specific features of the hierarchical microstructures at different length-scales provide a basis for the strengthening and toughening properties of this additively manufactured medium-entropy alloy. This correlation between the deformation and the hierarchical microstructures at different length-scales may provide future guidance for improving the fracture toughness properties of medium-entropy alloys.

Flexural and fracture behavior of additively manufactured carbon fiber reinforced polymer composites with bioinspired Bouligand meso-structures

Carbon fiber reinforced polymer (CFRP) composites are strong and lightweight materials extensively used across aerospace, automotive, and construction industries. Bioinspired designs such as Bouligand structures have the potential to improve the mechanical properties of CFRP composites. In this study, we examine the effects of the single and double Bouligand meso-structures with varying twist angles on the flexural and fracture properties of additively manufactured continuous CFRP composites. 3-point flexural tests are conducted to characterize the flexural properties such as flexural modulus, strength, and energy absorption. Single edge notch bend (SENB) tests are performed to quantitively characterize the mode I fracture toughness and effective fracture energy. The elasto-plastic fracture theory is used to quantify the contributions of elastic and plastic energies to the effective fracture energy. Experimental results indicate that twist angles significantly affect the flexural behavior of CFRP composites. The Bouligand meso-structures with a twist angle of 10° increase the flexural strain energy absorption by 2-3 times. The single and double Bouligand layup configurations with the same twist angle result in different flexural properties. In addition, the twist angle affects the magnitude of fracture toughness. A twist angle of 10° results in an improvement of up to 60% in fracture energy dissipation compared to the quasi-isotropic meso-structure. The single and double Bouligand meso-structures with the same twist angle exhibit almost the same fracture toughness and absorbed fracture energy. The Bouligand meso-structures do not increase fracture toughness and elastic fracture energy for crack initiation compared to the quasi-isotropic meso-structure.

High damage-resistance and fracture toughness of transparent Nb-doped barium aluminoborate glass ceramics

Glass-ceramics offer the opportunity to address the main disadvantage of oxide glasses, namely low fracture toughness. The presence of crystals can improve the fracture toughness (crack growth resistance), but the crack initiation resistance will typically be deteriorated due to the induced residual stresses. Excessive crystal content and large crystal size can also lead to a loss of transparency. In this work, we report a Nb-doped barium aluminoborate glass-ceramic, for which both the crack initiation resistance (CR) and fracture toughness (KIc) get improved upon heat treatment, while still maintaining some transparency. Relying on combined structural and mechanical characterizations, we demonstrate that the coordination numbers of B and Al in the glass phase decrease upon heat treatment, which is beneficial to energy dissipation under mechanical stress to improve CR. Furthermore, the formed piezoelectric crystal phase BaNb2O6 also helps to improve both CR and KIc, likely by converting the stress-induced mechanical energy into electric energy. Meanwhile, the increase in crystallinity and crystal size after heat treatment also leads to higher KIc of the glass-ceramics. These findings thus help address the difficult problem of simultaneously improving the resistances to crack initiation and growth, which will facilitate the future design of transparent, yet highly damage-resistant and damage-tolerant glass ceramics.

In-situ observation of fracture behaviors in TiB2p/Al7050 composites with different gradient structure

The study employed the vacuum hot-pressed sintering method to fabricate TiB2p/Al7050 homogeneous composites (HC) and TiB2p/Al7050 functionally gradient materials (FGM), including three-layer conventional FGM (TFGM) and five-layer bionic interleaved FGM (FFGM). The crack-initiation fracture toughness (KIc), crack-propagation fracture toughness (KJc), and crack propagation performance were investigated to examine the impact of gradient structure and TiB2p content. The results highlighted the crucial role of TiB2p content in determining the fracture toughness of the three composites. The fracture toughness of HC requires consideration of the synergistic effects of strength and plasticity, while that of FGM is influenced by the combined effects of strength, plasticity, and interlayer synergistic factors. Additionally, the in-situ observation of the crack propagation path revealed a toughening mechanism that contributes to the improved fracture toughness of these composites. This mechanism includes crack deflection, branching, plastic deformation of the matrix, and crack blunting, which consumes the energy required for crack propagation, reduces the stress concentration at the main crack tip, and delays crack propagation. It is worth mentioning that among these composite materials, FFGM demonstrates the highest fracture toughness, with KIc and KJc increasing up to 22.39% and 22.23% above the average, respectively. The excellent performance can be attributed to its highly effective toughening mechanism. Overall, the study provides valuable insights into the design and development of FGM with superior fracture resistance. Hence, these findings can support the development of advanced materials with improved toughness and potential applications in various fields.

Impact of low temperature and NaCl attack on the fracture properties of engineered cementitious composites (ECC)

Engineered cementitious composites (ECC) is a potential reinforcement and repair material for hydraulic structures due to its excellent mechanical properties. However, the fracture properties of ECC under the coupling effect of low temperature and chloride ions attack are still unclear. In this study, fracture experiments were performed on ECC specimens under different working conditions (immersed in water and NaCl solutions for different time (0, 30, 60, and 90d) and undergoing different freeze-thaw cycles (0, 25, 50, and 100 cycles) in NaCl solution) at experimental temperatures of 20 °C and −20 °C. The relationship between the depth of chloride ions erosion and the nominal fracture energy was analyzed. The effect of the coupled of temperature and chloride ions attack on the fracture performance of ECC under different working conditions was investigated. The results showed that: Under the loading condition of −20 °C, the fracture parameters of ECC under NaCl solution immersion were all lower than those of the water immersion group, indicating that extravasated chloride ions negatively impacted ECC's fracture properties. When ECC was loaded at −20 °C, the initiation fracture toughness and unstable fracture toughness of ECC under NaCl solution immersion were lower than those of the water immersion group, but the fracture energy was larger than that of the water immersion group, and when the specimens were immersed for 90 days, the drop in the fracture energy of ECC loaded at −20 °C compared to 20 °C for the NaCl solution immersion group was 59.1% less than 62.7% for the water immersion group; While loading at 20 °C revealed a linearly declining relationship between erosion depth and fracture energy, loading at −20 °C revealed no discernible pattern. The crack initiation fracture toughness of ECC gradually decreased with the increase of the freeze-thaw cycles, but the specimens' crack initiation fracture toughness following NaCl freezing at −20 °C was consistently larger than that at 20 °C. Following 100 freeze-thaw cycles on the specimens, the increase in initiation fracture toughness at −20 °C compared to 20 °C for the water freeze-thaw group was 128.4% less than that of the salt freeze-thaw group, which was 135.8%, while the decrease in fracture energy was 19.9% less than that of the salt freeze-thaw group, which was 46.3%. It shows that the repair effect of ice on ECC after NaCl freeze-thaw cycles is stronger than that of water freezing at the low temperature.

Test method for fracture toughness GIC based on ubiquitiform theory

A new fracture toughness test method for obtaining the crack initiation fracture toughness GIC and crack propagation fracture toughness GC was proposed. This method was based on the basic idea of ubiquitiform geometry and experimental results showing that material fracture surfaces possess ubiquitiform characteristics. A uniaxial tensile test was performed on plate specimens with cracks made by ductilecast iron to generate Mode I fracture failure. Loading–displacement curves were recorded in accordance with the experimental process, and the crack-initiation work W1 and the crack propagation work W2 were recorded. The morphology of the fracture surface was observed through electron microscopy, and the ubiquitiformal complexity D of the fracture surface was calculated on the basis of ubiquitiform theory. The ubiquitiform fracture area of the fracture surface was further obtained. The formula for ubiquitiform fracture energy was provided and used to calculate the ubiquitiform fracture energies Guf1 and Guf2 of the tested material. By analyzing the relationship between the above ubiquitiform fracture energy and fracture toughness GIC, a test method for determining fracture toughness based on ubiquitiform fracture energy was proposed. The experimental fracture toughness test results for several cracks of different sizes were consistent within a certain range of crack lengths.

FRACTURE PROPERTIE ANALYSIS OF RECYCLED AGGREGATE CONCRETE BASED ON DIGITAL IMAGE CORRELATION TECHNIQUE

Three point bending fracture tests of recycled aggregate concrete beams with different recycled coarse aggregate replacement ratio (0%, 30%, 50%, 70%, 100%) have been carried out, with results analyzed by digital image correlation (DIC) method and the traditional electrometric method. The double-K fracture parameters, crack-mouth-opening displacement (CMOD), crack-tip-opening displacement (CTOD), crack extension length ( \begin{document}$\Delta a$\end{document} ) and fracture growth path were obtained, and the validity of DIC method was verified. The results show that when the replacement rate is 100%, the crack initiation fracture toughness and unstable fracture toughness of recycled aggregate concrete decrease by 15.81% and 15.39%, respectively. With the increase of the replacement rate of recycled aggregate, the slopes of the descending sections of P-CMOD, P-CTOD and P- \begin{document}$\Delta a$\end{document} curves increase. DIC method can effectively capture the fracture propagation process. The CMOD values measured by DIC method and clip type extenometer are in good agreement. The variation trends of DIC measured value and formula-calculated value of CTOD are relatively consistent. Based on the test results, the estimated values, \begin{document}$\Delta a$\end{document} , of specimens with different replacement rates of recycled aggregate under different loads can be obtained by fitting the curve between \begin{document}$P$\end{document} / \begin{document}${P_{\max }}$\end{document} and \begin{document}$\Delta a$\end{document} / \begin{document}$\Delta {a_{\text{c}}}$\end{document} .

A novel nacre-like metal/metal structure by lithography and electrodeposition

Taking a leaf out of Nature’s book, the use of nacre-like structure in the materials synthesis has generated notable successes in creating novel structural composites but has yielded few practical advances in metals. Here we have successfully architected the intricate hierarchical microstructure, the brick-and-mortar structure, in metal/metal hybrids simply by deploying the coupling of lithographic method and electrodeposition technique, which allows the accurate control over the size, volume fraction and shape of the brick, amorphous Ni-P alloy or nanocrystalline Ni, and the formation of a fully interconnected mortar phase, ultrafine-grained Ni or Cu. Tensile testing results show that these innovative composites exhibit an enhanced crack-initiation fracture toughness, and their fracture behaviors have a strong dependency on the initial notch/crack orientation. Our work removes restrictions on the design and synthesis of the real nacre-like metal/metal structure, and provides a promising strategy for developing advanced metals by taking advantages of complex 3 demension brick-and-mortar structure and intricate interface architectures.

Artificial neural network technique to predict dynamic fracture of particulate composite

In this paper, the artificial neural network technique using a multi-layer perceptron feed forward scheme was used to model and predict the mode-I fracture behaviour of particulate polymer composites when subjected to impact loading. A neural network consisting of three-layers was employed to develop the network. Artificial neural network was constructed using six input parameters such as shear wave speed ( CS), density ( D), elastic modulus ( Ed), longitudinal wave speed ( CL), volume fraction ( Vf) and time ( t). The influence of input parameters on the output stress intensity factor and crack-initiation fracture toughness were found to be in the order of t > CS > D > Ed > CL > Vf. The degree of accuracy of prediction was 92.7% for stress intensity factor. In this regard, artificial neural network can be used in the modelling and prediction of fracture behaviour of particulate polymer composites under impact loading.

Phase field model for simulating the fracture behaviors of some disc-type specimens

A staggered scheme for phase field modeling of brittle fractures is implemented to simulate mixed mode fracturing of disc-type specimens. The crack propagation process and load-displacement curves of each type of disc specimen are investigated. The effects of specimen geometry and loading mode on the crack propagation process and load-displacement curves are studied. The predicted results for crack initiation angle and fracture toughness obtained by the phase field method are compared with the analytical solutions. The results show that the crack initiation angle and fracture toughness obtained by the phase field method agree well with those determined by the generalized maximum tangential stress (GMTS) criterion. This implies that the phase field method has high accuracy in simulating the problem of crack-weakened Brazilian discs.

Determination of double-K fracture toughness parameters of thermally treated granite using notched semi-circular bending specimen

The safety of cracked rock structures after thermal treatment is the concern of many existing engineering programs. To obtain a deep understanding of rock fracture process, mode I fracture tests are carried out on thermally treated granite (from 25 °C to 800 °C) using notched semi-circular bending (NSCB) specimens in this paper. An acoustic emission (AE) technique is employed to monitor the real-time AE activities during the whole deformation process. The double-K parameters extracted from the double-K fracture model are applied to depict the fracture process of the heat-treated granite NSCB specimens. When the temperature rises from 25 °C to 800 °C, rock density, porosity, elastic modulus, and Poisson's ratio all show variations to some extent. The heat treatment decreases the rock density, elastic modulus, and Poisson's ratio, while it increases the rock porosity. Fracture tests show that the rock fracture behaviours gradually change from brittle fracture to ductile fracture when the thermal treatment temperature exceeds 300 °C: i.e., the start temperature of brittle–ductile transition. AE results show that the crack initiation load and peak load agree well with the AE activity characteristics during the entire loading process. It is observed that the crack initiation fracture toughness KICini and the unstable fracture toughness KICun from double-K fracture model can be successfully applied to describe the rock fracture. When the temperature ranges from 25 °C to 300 °C, KICini and KICun are not sensitive to temperature. However, as temperature ascends over 300 °C, KICini and KICun almost linearly decrease with temperature. The decline in KICini and KICun demonstrates that the rock has gradually lost its ability to withstand cracking from initiation and propagation. This paper aims to better understand the mode I fracture of thermally treated rocks and initially explore and determine the double-K fracture toughness parameters of thermally treated rocks with NSCB specimens.

Dynamic delamination on elastic interface

The dynamic energy release rate (ERR) is derived for a delamination on the interface between a partially supported vibrating beam and an elastic foundation, with a time-dependent displacement applied to the beam’s free end. The configuration may represent, for example, the dynamic delamination of a laminated composite, or the cracking of a typical adhesively bonded composite joint. The developed theory is completely analytical and applicable to both symmetric double cantilever beams (DCBs) and thin layers on thick substrates. It was discovered that the dispersive propagation of flexural waves should be considered in order to capture contributions to the ERR from higher-order vibration modes. The developed theory is verified using finite-element-method (FEM) simulations and they are found to be in excellent agreement. This work will be useful to characterize the dynamic fracture toughness of layered materials in DCB tests, and to determine the fracture behavior of engineering structures under dynamic loads. Furthermore, the partially supported beam’s elastic foundation is relevant for the study of crack process zones, which are usually analyzed using the FEM and the cohesive-zone model. The potential applications of this study include determining the dynamic fracture toughness for crack initiation in laminated composite DCBs and adhesively bonded structures.

Relation between impact and fracture toughness of A-387 Gr. B welded joint

The influence of temperature on impact and fracture toughness values in different regions of a welded joint is analysed for low-alloyed Cr-Mo steel A-387 Gr. B, designed for high temperature applications. Standard Charpy specimens were tested on instrumented pendulum to separate total impact energy into energy for initiation and propagation energy for base metal (BM), weld metal (WM) and heat-affected-zone (HAZ). Standard three point bending (3BP) specimens with crack tip located at different regions of a joint (BM, WM, HAZ), were used for fracture toughness testing. Experiments were performed both at the room temperature and at design working temperature, 5400 C, which is the focus of this paper, to evaluate temperature effect on both notch and crack resistance for all different regions in a welded joint. Moreover, the relation between crack initiation energy and fracture toughness is established, purely on empirical base.

The influence of impacting orientations on the failure modes of cracked tunnel

Underground tunnels are often subjected to dynamic loadings, and the dynamic loadings may come from various directions. To study the influence of loading orientations on the failure modes of cracked tunnels, laboratory impact experiments were conducted by a drop weight testing apparatus with synchronized measuring system. Green sandstone was selected as the experimental material to fabricate the tunnel samples, a pre-crack emanating from tunnel roof was designed to simulate the natural crack around a tunnel. In the process of dynamic loading tests, strain gauges were employed to determine crack time-to-fracture and crack velocity. Numerical simulation was carried out by the finite element software ABAQUS and the finite difference software AUTODYN. Crack initiation fracture toughness (IFT) was evaluated by experimental-numerical technique and the failure behavior of tunnel model under different orientation impacts was presented in this paper. The studying results show that as impacts come from tunnel roof, tunnel failure mainly occurs near the crack tip and the tunnel bottom (or the tunnel foot); as impact come from tunnel sidewall, the tunnel failure only occurs at the two sides of arch shoulder. The dynamic initiation fracture toughness of the pre-crack in the tunnel models is greatly related to the impact loading orientations.

Bone collagen network integrity and transverse fracture toughness of human cortical bone.

Greater understanding of the determinants of skeletal fragility is highly sought due to the great burden that bone affecting diseases and fractures have on economies, societies and health care systems. Being a complex, hierarchical composite of collagen type-I and non-stoichiometric substituted hydroxyapatite, bone derives toughness from its organic phase. In this study, we tested whether early observations that a strong correlation between bone collagen integrity measured by thermomechanical methods and work to fracture exist in a more general and heterogeneous sampling of the population. Neighboring uniform specimens from an established, highly characterized and previously published collection of human cortical bone samples (femur mid-shaft) were decalcified in EDTA. Fifty-four of the original 62 donors were included (26 male and 28 females; ages 21-101 years; aging, osteoporosis, diabetes and cancer). Following decalcification, bone collagen was tested using hydrothermal isometric tension (HIT) testing in order to measure the collagen's thermal stability (denaturation temperature, Td) and network connectivity (maximum rate of isometric tension generation; Max.Slope). We used linear regression and general linear models (GLMs) with several explanatory variables to determine whether relationships between HIT parameters and generally accepted bone quality factors (e.g., cortical porosity, pentosidine content [pen], pyridinoline content [pyd]), age, and measures of fracture toughness (crack initiation fracture toughness, Kinit, and total energy release/dissipation rate evaluated at the point of unstable fast fracture, J-int) were significant. Bone collagen connectivity (Max.Slope) correlated well with the measures of fracture toughness (R2 = 24-35%), and to a lesser degree with bound water fraction (BW; R2 = 7.9%) and pore water fraction (PW; R2 = 9.1%). Significant correlations with age, apparent volumetric bone mineral density (vBMD), and mature enzymatic [pyd] and non-enzymatic collagen crosslinks [pen] were not detected. GLMs found that Max.Slope and vBMD (or BW), with or without age as additional covariate, all significantly explained the variance in Kinit (adjusted-R2 = 36.7-49.0%). Also, the best-fit model for J-int (adjusted-R2 = 35.7%) included only age and Max.Slope as explanatory variables with Max.Slope contributing twice as much as age. Max.Slope and BW without age were also significant predictors of J-int (adjusted-R2 = 35.5%). In conclusion, bone collagen integrity as measured by thermomechanical methods is a key factor in cortical bone fracture toughness. This study further demonstrates that greater attention should be paid to degradation of the overall organic phase, rather than a specific biomarker (e.g. [pen]), when seeking to understand elevated fracture rates in aging and disease.