Lower Toughness Values Research Articles

Changes in the material properties of spider glue droplet proteins accompanied shifts in prey capture biomechanics as cobweb spiders diverged from their orb weaving ancestors

Although descended from orb weavers, spiders in the family Theridiidae spin cobwebs whose sticky prey capture gumfoot lines extend from a silk tangle to a surface below. When a crawling insect contacts glue droplets at the bottom of a gumfoot line, the line's weak pyriform anchor releases, causing the taut line to contract, pulling the insect from the surface and making its struggles to escape ineffective. To determine if this change in prey capture biomechanics was accompanied by a change in the material properties of theridiid glue, we characterized the elastic modulus and toughness of the glue droplet proteins of four theridiid species at 20–90 % relative humidity and compared their properties with those of 13 orb weaving species in the families Tetragnathidae and Araneidae. Compared to orb weavers, theridiid glue proteins had low extensions per protein volume and low elastic modulus and toughness values. These differences are likely explained by the loss of tension on a gumfoot line when its anchor fails, which may prioritize glue droplet adhesion rather than extension. Similarities in theridiid glue droplet properties did not reflect these species’ evolutionary relationships. Instead, they appear associated with differences in web architecture. Two species that had stiffer gumfoot support lines and longer and more closely spaced gumfoot lines also had stiffer glue proteins. These lines may store more energy, and, when their anchors release, require stiffer glue to resist the more forceful upward thrust of a prey. Statement of significanceWhen a crawling insect contacts glue droplets on a theridiid cobweb's gumfoot line, this taut line's anchor fails and the insect is hoisted upward, rendering its struggles to escape ineffective. This strategy contrasts with that of orb weaving ancestors, which rely on more closely spaced prey capture threads to intercept and retain flying insects. A comparison of the elastic modulus and toughness of gumfoot and orb web glue proteins shows that this change in prey capture biomechanics is associated with reductions in the stiffness and toughness of cobweb glue. Unlike orb web capture threads, whose droplets extend in a coordinated fashion to sum adhesive forces, gumfoot lines become untethered, which prioritizes glue droplet adhesive contact over glue droplet extension.

Laser-Powder Bed Fusion Additive Manufacturing of NiCrBSi Self-Fluxing Nickel Alloy, Material Health - Process Relationship

Laser Powder Bed Fusion (L-PBF) might be a promising solution for producing complex wear-resistant parts from NiCrBSi self-fluxing nickel alloys. This study investigates a large set of parameters with a baseplate heated up to 500 °C. Furthermore, laser remelting is also explored to further increase surface density and reduce cracking. Material health is deeply investigated by image analysis to quantify different defects (lack of fusion, porosity and cracks). Spatters likely induce lacks of fusion, while the low toughness and high hardness values cause cracks. The lack of fusion surface fraction and crack length decrease with the preheating temperature while the crack width increases. A surface density of 99 % is obtained with careful process optimisation leading to a laser power of 100 W, a laser speed of 750 mm.s-1 and a preheating temperature of 500 °C.

Role of Nanoscale Heterogeneity in the Mechanical Performance of Hybrid Elastomers

Silicone–organic interpenetrating polymer networks (IPNs) are hybrid materials with enhanced mechanical properties relative to pure silicones. Here, we compare structure–property relationships of graft-IPNs of polydimethylsiloxane (PDMS) made with methyl methacrylate (MMA) and isobornyl methacrylate (IBoMA). We found evidence for increased polymer–polymer mixing in the PDMS/PIBoMA graft-IPNs, which was impacted by the higher relative compatibility of these two polymers compared to PDMS/PMMA. These PDMS/PIBoMA hybrid materials possessed fracture toughness values up to 400× greater than unreinforced PDMS elastomers, contrasted by the lower toughness values and highly phase separated morphologies of the PDMS/PMMA hybrids. Increased temperature reduced the fracture and fatigue resistance of the hybrids as nanoscale mechanical heterogeneity was lost between PDMS and the methacrylate polymers, which is consistent with the behavior of existent silicone resin-filled silicone materials.

Remarkably high fracture toughness of HfNbTaTiZr refractory high-entropy alloy

• The fracture behavior of the Hfnbtatizr refractory HEA was investigated. • The HEA exhibits a remarkably high fracture toughness of K JIC = 211 MPa•m 1/2 . • Fully-ductile fracture mode with the formation of kink bands was observed. • The excellent damage-tolerance plus high strengths in a wide temperature range endow this HEA a promising structural material. High-entropy alloys (HEAs) with face-centered cubic (FCC) phase such as CoCrFeMnNi or CoCrNi generally exhibit ultra-high fracture toughness but relatively low strength. In contrast, body-centered cubic (BCC) HEAs often display higher strengths, but the few reports on fracture toughness measurement demonstrate low toughness values. Here we show that the BCC HfNbTaTiZr refractory HEA, which possesses a combination of high strength, good tensile ductility and excellent high-temperature properties, also exhibits a remarkably high fracture toughness. By using the "single specimen" compliance method for J -integral measurement according to the ASTM E1820–17 standard, its fracture toughness K JIC was experimentally determined to be 210 MPa m 1/2 , which renders this HEA among the toughest metallic materials. The excellent damage tolerance makes the HEA promising for applications as high-temperature structural materials such as in aerospace field.

Influence of Fiber Volume in Hybrid Short Glass/Cellulose Reinforced Thermoplastic Compounds

Glass fibers (GF) and regenerated cellulose fibers (RCF) are possible partners in the hybrid reinforcement of thermoplastics because of their different properties. Due to the weak bonding properties of polypropylene, coupling agents are used and the fiber volume content is set high to achieve high reinforcing effects. A lower fiber content of GF can raise the toughness properties of a reinforced polypropylene which is investigated in this study with different ratios of GF and RCF. The composites are tested in tensile tests, flexural tests and also in notched Charpy impact tests. The results can be used to compare whether a substitution of GF with RCF or the addition of more GF leads to higher mechanical properties. The tensile and Charpy impact results are compared with the Rule of Hybrid Mixtures (RoHM) to show the deviation to the prediction. Better results in terms of stiffness and strength are seen with a higher total fiber volume, while hybrid reinforced specimens show lower toughness values compared to the RCF reinforced reference specimens. Adding 5 vol% GF to 16 vol% RCF results in an increase in tensile strength by 26%, but also a significant decrease in elongation at break by 65%.

Effect of the notch location on the Charpy-V toughness results for robotic flux-cored arc welded multipass joints

Abstract In this study, the effect of the notch locations on the Charpy-V toughness values of the all-welded joint obtained using robotic flux-cored arc welding was investigated with respect to microstructures at the notch locations. Charpy impact tests were performed through the thickness with notch location at the centerline as well as off-set regions of the weld metal in addition to the microhardness measurements conducted. The detailed weld metal characterization was conducted using a stereo microscope, optical microscope, and scanning electron microscope at the same location where the Charpy tests and microhardness tests were performed. The sub-zero impact toughness test results indicated that the columnar weld metal regions exhibited low toughness values while the centerline microstructure consisting of mainly reheated regions displayed much higher toughness values even at the test temperature of −60 °C, satisfying the toughness requirement of the requested 47 J value. It is concluded that a small variation of the through-thickness notch position may result in different toughness values for the same weld metal. On this basis, the notching procedure of the Charpy-V samples for the multi-pass weld metal should be conducted with care and obtained results should be explained with respective notch position and microstructure.

Role of Plasticizers on PHB/bio-TPE Blends Compatibilized by Reactive Extrusion.

Poly(hydroxybutyrate) (PHB) is a biopolymer biologically synthesized by controlled bacterial fermentation from a wide variety of microorganisms. PHB is proposed as a potential green alternative to commonly used plastics in packaging, due to its biodegradability and biocompatibility. However, if PHB is to replace commodities, it has some limitations regarding its thermo-mechanical performance to overcome. Among them are its critically the low toughness values at room temperature and poor thermoforming ability. With the aim of overcoming these weaknesses, in this work, blends of PHB with the addition of a biodegradable thermoplastic elastomer (bio-TPE) were prepared and evaluated. Films of such compounds were made by cast extrusion. In order to enhance the compatibility of both polymers during the extrusion process, three different reactive agents (poly-hexametylene diisocianate, triglycidyl isocyanurate, and Joncryl® ADR-4368) were assessed. The morphology and mechanical- and thermal properties of the films obtained were analyzed. In addition, the thermoforming ability of the produced films was evaluated. The results show that the plasticizers present in the bio-TPE interacted with the reactive agents, making them chemical competitors and altering the outcome of the blends.

Use of fibres in improving the mechanical properties of a multifunctional cement for structural repair purposes

Calcium phosphate cement (CPC) is a multifunctional cement whose potential application depends on the reactants used to synthesise it. Just like many inorganic cements, the pure CPCs synthesised in all cases are very brittle and have low toughness values under loading. In this research, the CPC material is formed from the exothermic reaction between phosphoric acid and calcium silicate at controlled room temperature. Three fibre types, namely; macro polypropylene fibres, amorphous metallic fibres and recycled carbon fibres were chosen due to their corrosion resistance in acid to enhance the mechanical performance of this cement as a repair material. 1.5% by volume of each of these fibres were added to the CPC material and autogenously cured for 14 days at room temperature. Mechanical destructive and non-destructive tests were carried out on the resulting composites. The experimental results revealed that each type of fibre contributes to increase flexural strength, compressive strength, fracture energy and dynamic elastic modulus of CPC material. However, for this purpose the recycled carbon fibres have proven to be more efficient.

Dissimilar Rotary Friction Welding of Inconel 718 to F22 Using Inconel 625 Interlayer

Dissimilar metal joining has always been a challenging task because of the metallurgical incompatibility and difference in melting points of alloys being joined. Diffusion and mixing of alloying elements from dissimilar base metals at the weld often cause unwanted metallurgical changes resulting in unsuccessful welds or underperformance of the weldment. Solid-state dissimilar friction welds of Inconel 718 and F22 were prepared in this study with an Inconel 625 interlayer to address the carbon enrichment of Inconel 718 during the welding. Defect-free rotary friction welds were produced in this study. Microstructural and mechanical properties investigation of the weldments and base metals was carried out, and results were analysed. Intermixing zone was observed at the weld interface due to the softening of the metal at the interface and rotatory motion during the welding. The high temperatures and the plastic deformation of the intermixing zone and thermo-mechanically affected zone (TMAZ) resulted in the grain refinement of the weld region. The highest hardness was observed at the Inconel 718/F22 weld interface due to the plastic strain and the carbon diffusion. The tensile specimens failed in the F22 base metal for the weld prepared with and without the Inconel 625 interlayer. Inconel 718/F22 welds exhibited lower toughness values compared to the Inconel 718/F22 welds prepared with Inconel 625 interlayer.

Effect of activated flux tungsten inert gas (A-TIG) welding on the mechanical properties and the metallurgical and corrosion assessment of Inconel 625

This article makes an attempt to investigate the outcome of activated flux and filler wire in addition to A-TIG welding and TIG welding of Inconel 625 respectively. Ni-Cr-Mo enriched filler namely ERNiCrMo-3 was used to join 6.5-mm-thick plates. Microstructure characterization, mechanical properties evaluation and secondary dendritic arm spacing measurements were carried out to find the cause of the perceived differences. Tensile test failures were observed at the weld zone in both welding processes. Charpy impact studies showed that weldment using A-TIG revealed a low toughness value compared to the TIG weldment. Root bend test showed no discontinuity in both fusion zones and hence, the weldment was produced without defect. The deleterious laves phase was reduced when activated flux and fillers were used. Corrosion performance was undertaken in a 3.5 wt% NaCl solution, to illustrate the outstanding corrosion resistance in Inconel 625’s fusion zone using A-TIG and TIG welding processes.

Investigation of microstructure and mechanical properties of AISI2205/DIN-P355GH steel joint by submerged arc welding

• In this study, AISI 2205 duplex stainless steel materials and P355GH pressure vessel steels are joined by using the same additional metal and powder, with the same parameters and submerged arc welding method. • Welded with SAW method, these materials were tested by eye, magnetic particle and radiographic examination methods to detect surface and sub-surface defects. No pores, voids or cracks were found in the materials after the magnetic particle test and radiographic test. In addition, solid spot and fixation of the welded samples worked, and welded samples showed no unacceptable angular distortion and high-low defect error. • Tensile, bending, impact notch and hardness tests were applied to determine the mechanical properties of welded samples. When the tensile test results are examined, it is seen that although the highest tensile strength of the main materials is in AISI2205 material, % elongation values are very close to each other. • Successful results have been achieved from all SAW of duplex stainless steel and pressure vessel steels. This result shows that additional metal, welding flux and welding parameters are suitable for joining duplex stainless steel and pressure vessel steels. In this study, duplex stainless (AISI2205) steel and pressure vessel (P355GH) steel have been joined by submerged arc welding method (SAW). Three different joining operations (AISI2205-AISI2205), (P355GH-P355GH) and (AISI2205-P355GH) were performed respectively. ELOX UP 309 L submerged arc welding wire and Eliflux Bss-A submerged arc welding powder were used for joining materials. Welded materials have been tested with eye, magnetic particle and radiographic examination methods were used to detect surface and subsurface defects. Tensile, bending, Charpy impact notch and hardness tests were then performed to determine the mechanical properties of welded samples. Additionally, microstructure investigations were made to determine the structural changes in the welding zone. Various NDE technqiues were adopted to investigate the quality of the welds. As a result of tensile tests, the rupture was made of welding metal in AISI2205-AISI2205 joints and P355GH in other joints was made of base material. No visible errors were observed in the welding area after bending test. When the V-notch impact energies of the materials were compared, the highest toughness value was measured in the ITAB of AISI2205 material and the lowest toughness value was measured in the P355GH weld metal. In hardness measurements, the highest hardness value was obtained in the HAZ of the AISI2205 material, whereas the lowest hardness was measured in the P355GH base material. Microstructure studies indicated that the weld metal comprised a dendritic structure, and the grains were observed to become coarse in the region adjacent to the melting boundary on the main material side.

Chromium effects on the microstructural, mechanical and thermal properties of a rapidly solidified eutectic Sn-Ag alloy

PurposeThis study aims to investigate the chromium (Cr) effects on the microstructural, mechanical and thermal properties of melt-spun Sn-3.5Ag alloy.Design/methodology/approachTernary melt-spun Sn-Ag-Cr alloys were investigated using X-ray diffractions, scanning electron microscope, dynamic resonance technique, instron machine, Vickers hardness tester and differential scanning calorimetry.FindingsThe results revealed that the Ag3Sn intermetallic compound (IMC) and ß-Sn have been refined because of the hard inclusions’ (Cr atoms) effects, causing lattice distortion increasing these alloys. The tensile results of Sn96.4-Ag3.5-Cr0.1 alloy showed an improvement in Young’s modulus more than 100 per cent (42.16 GPa), ultimate tensile strength (UTS) by 9.4 per cent (23.9 MPa), compared with the eutectic Sn-Ag alloy due to the high concentration of Ag3Sn and their uniform distribution. Shortage in the internal friction (Q−1) of about 54 per cent (45.1) and increase in Vickers hardness of about 7.4 per cent (142.1 MPa) were also noted. Hexagonal Ag3Sn formation led to low toughness values compared to the eutectic Sn-Ag alloy, which may have resulted from the mismatching among hexagonal Ag3Sn phase with orthorhombic Ag3Sn and ß-Sn phases. Mechanically, the values of Young’s modulus have been increased, with increasing chromium content, whereas the UTS and toughness values have been decreased. The opposite of this trend appeared in Sn95.8-Ag3.5-Cr0.7 alloy, which may have been due to high lattice distortion (ƹ = 16.5 × 10−4) compared to the other alloys. Increase in the melting temperature Tm, ΔH, Cp and ΔT was because of Ag3Sn IMC formation. The low toughness of Sn96-Ag3.5-Cr0.5 and Sn95.8-Ag3.5-Cr0.7 (109.56 J/m3 and 35.66 J/m3), relatively high melting temperature Tm (223.22°C and 222.65°C) and low thermal conductivity and thermal diffusivity (32.651 w.m−1.k−1 and 0.314 m2/s) make them undesirable in the soldering process. The high UTS, high E, high thermal conductivity and diffusivity, low creep rate and low electrical resistivity, which have occurred with “0.1 Wt.%” of Cr, make this alloy desirable and reliable for soldering applications and electronic assembly.Originality/valueThis study provides chromium effects on the structure of the eutectic Sn-Ag rapidly solidified by melt-spinning technique. In this paper, the authors compared the elastic modulus of the melt-spun compositions, which have been resulted from the Static method with that have been resulted from the Dynamic method. This paper presents new improvements in mechanical and thermal performance.

Poly(furfuryl alcohol) bioresin-modified LY5210 epoxy thermosets

This study deals with the preparation of bio-based epoxy blends and of their mechanical, thermal, and morphological characterization. Thus, the commercial tetra-functional epoxy resin, LY5210, and various weight fractions of poly(furfuryl alcohol), PFA, were subjected into curing reaction by employing diethylenetriamine (DETA) as a curing agent. Mechanical properties of the intact resin as well as the epoxy-PFA blends have been explored to show the influence of the incorporated PFA on the epoxy matrix. Dynamic mechanical thermal analysis (DMTA) revealed that the blends had slightly lower storage modulus than that of the neat epoxy. Interestingly, in tensile analysis, epoxy-PFA blends exhibited higher elastic modulus and lower toughness values. Surface study of the modified samples was characterized by scanning electron microscopy (SEM), and morphological results confirmed the mechanical analyses results. Finally, the adhesion properties of resultant blends have been evaluated by subjecting them on to steel substrate and obtained results were correlated to mechanical properties. Generally, the results suggested the replacement of fossil-resourced epoxy resin with the PFA bio-based resin up to 25 wt% with negligible effect on mechanical and thermal properties. This achievement is important because the bioresin moieties may favor the environmental degradation of the thermoset network.

Hydraulic fracture geometry in ultrasoft polymer networks

Determination of failure properties becomes extremely challenging when materials approach very low moduli ( $$< 100$$ kPa) and toughness values. New techniques are emerging to address these challenges in order to facilitate advancement of accurate tissue phantoms and medical diagnostics. We report on needle-induced ‘cavitations’ within a series of silicone elastomer formulations to demonstrate the ability of hydraulically-induced fracture morphology to differentiate fracture behavior in ultrasoft solids. We show, in accordance with previous results by Lefevre et al. (Int J Fract 192:1–23. https://doi.org/10.1007/s10704-014-9982-0 . ISSN 15732673, 2015), that cavities first grow elastically and then transition to a penny-shape with an associated ring crack. Further growth occurs predominantly at the ring crack, leading to variations in cavity anisotropy quantified via the cavity’s sphericity. Sphericity differentiates between materials of identical, ultralow modulus, but distinct formulation. We find that materials for which modulus is lowered by decreasing the crosslinker to pre-polymer ratio are tougher than materials in which modulus is lowered through the addition of unreactive silicone oil. We conclude that cavity shape provides a promising avenue for fracture energy determination and that the ultrasoft silicone/diluted-silicone system studied here provides a material platform for altering fracture properties while holding modulus constant.

WC – (Cu: AISI304) composites processed from high energy ball milled powders

Alternative binders to cobalt, based on stainless steel (SS, AISI304) and copper were investigated for tungsten carbide (WC) based cemented carbides. The binder content was fixed at 12 wt%, and the Cu:SS ratio varied in proportions of 0:1, 1:5, 1:2, 1:1, 1:0. High energy ball milling was applied to ensure high homogenization, nanometric particle size and mechanical alloying of binder elements in the powders' mixtures. To assess an adequate sintering route, wettability testing and constant heating rate dilatometry in vacuum were performed. The composites were analyzed in terms of their structural, microstructural and mechanical characteristics.The poor wettability of melted Cu on WC surfaces was increased by alloying it with SS and highly dense compacts could be successfully attained at reduced vacuum sintering temperatures with binders having a Cu:SS ratio equal to or lower than 1:2. The microstructures show secondary phases and significant grain coarsening during sintering, whereas the average grain size was kept in the nanometric range. The composites that attained almost full densification present high hardness, comparable to that of nanometric WC-12Co cemented carbides processed by similar routes, but lower toughness values.

Role of cube texture on toughness variation of electric resistance welded steel

ABSTRACTProperties changes of an X52 microalloyed steel processed by a full-scale industrial electric resistant welding (ERW) equipment was studied. Lack of proper toughness level in the weld zone was investigated. Results show that the low toughness value could only be satisfactorily addressed after a two-stage annealing process. {100} pole figures for each processing step revealed a completely random texture for the initial plate. However, after the ERW process, a textured structure with the main components of brass, S and copper was obtained. Texture components were substantially weakened after the second stage of annealing and instead a cube texture was developed which could explain satisfactory level of toughness for the ERW pipe after conducting the two-step annealing process.

Brittle fracture analysis of Dissimilar Metal Welds between low-alloy steel and stainless steel at low temperatures

Dissimilar Metal Welds (DMW) between low-alloy steel (A533 steel) and austenitic 316L stainless steel are widely used within the French nuclear power plants where they connect the main components to the primary circuit pipes. In these DMW, the welding process and the post-weld heat-treatment generate a hard thin layer of carburized martensite and austenite in the vicinity of the fusion line (FL), resulting in a heterogeneous microstructure with high mechanical properties gradient, hence potentially, a higher sensitivity to brittle fracture in the hard layer. The present study aims to evaluate the brittle behavior of the DMW at low temperatures and more particularly of the interface between the carburized martensite and austenite (MA interface). Fracture toughness tests were carried out at temperatures between - 120°C and -50°C, with a precrack tip located on the ferritic side near the FL (i.e., between the ferritic steel and the stainless steel buttering). The analysis of the fracture behavior of the DMW was based on a SEM examination of CT (Compact Tension) specimens fracture surfaces. Coupled with a 2D plane strain numerical simulation of the tests, the results show that the presence of austenite in the fatigue precrack front and subsequent ductile tearing towards FL produced higher solicitations on the hard layer and caused intergranular fracture on the MA interface, resulting in lower toughness values for the specimen. To model the brittle behavior of the MA interface, a stress based criterion was used. Tensile tests on axisymmetric specimen, which were machined to initiate intergranular fracture in the MA interface and tested at -170°C, were used to define a threshold stress (σth), below which brittle fracture cannot occur. Then, a criterion to evaluate the brittle fracture risk of the DMW was proposed and applied to the CT specimen.

On the Microstructure, Hardness and Impact Toughness of 356 and 413 Alloys

The present study was performed on 356 and 413 alloys containing various amounts of hydrogen (H2), titanium diboride (TiB2) and strontium (Sr). The results show that the eutectic silicon particles in non-modified alloys undergo coarsening during the solutionizing treatment. A new mechanism, based on the Ostwald theory, has been proposed to explain the observed phenomenon. Although the variation in melt treatment parameters has no significant influence on the alloy hardness, it does have a great effect on the alloy impact toughness. Best results are obtained when the alloy is degassed, Sr-modified and grain refined. Also, Sr-modified, degassed 413 alloys have been found to possess good impact toughness. Precipitation of Mg2Si phase particles in 356 alloy is more effective as a hardening agent than the Al2Cu phase precipitated in the 413 alloy. The increased Si content in non-modified 413 alloys accelerates crack initiation and propagation, leading to low toughness values. Modifying the 413 alloys with 200 ppm Sr results in a more even distribution of the spheroidized eutectic Si particles and hence improves the alloy toughness.

Effect of metallurgical parameters on the microstructure, hardness impact properties, and fractography of Al-(6.5–11.5) wt% Si based alloys

The present study was performed on 356 and 413 alloys containing various amounts of hydrogen (H2), titanium diboride (TiB2), and strontium (Sr). The results show that the eutectic silicon particles in non-modified alloys undergo coarsening during the solutionizing treatment. High energy levels are obtained when the alloy is degassed, Sr-modified, and grain refined. Precipitation of Mg2Si phase particles in 356 alloys is more effective as a hardening agent than the Al2Cu phase precipitated in the 413 alloy which contributes to the alloy strength/hardness. The increased Si content in non-modified 413 alloys accelerates crack initiation and propagation, leading to low toughness values. Modifying the 413 alloys with 200ppm Sr results in a more even distribution of the spheroidized eutectic Si particles and hence better the alloy toughness. Exceeding the required amount of Ti-containing grain refiner may result in the introduction of a large amount of brittle Al3Ti platelets that would reduce the alloy toughness.

The fracture toughness of eggshell

The shells of avian eggs are very brittle, but how brittle? Fracture toughness, Kc is a standard measure used widely to characterise engineering materials. We devised a novel way to measure Kc and applied it to commercial hens’ eggs, obtaining a value of 0.3MPa√m. This value is much lower than previous published values, which we argue are incorrect and misleading. We discuss how this exceptionally low toughness value (in comparison to that of other natural materials made from calcium carbonate) has been achieved by prevention of toughening mechanisms. Eggshell has an unusual combination of mechanical properties (low fracture toughness combined with high Young’s modulus), making it ideally suited as a container for the developing chick, which must be stiff and rigid but also brittle enough to be broken when required. Further testing and analysis using the Theory of Critical Distances and Weibull probability theory allowed us to describe the effects of defects of various types: cracks, holes and notches, on the strength of whole eggs. These results are of commercial importance because many eggs break prematurely as a result of microscopic defects. Statement of SignificanceThis paper presents the first accurate measurements of the fracture toughness of eggshell. These results are important because eggshell is a brittle material which fails from microscopic defects, so knowledge of the fracture toughness is essential to understand its mechanical performance.The toughness value obtained is discussed in the context of other mechanical properties, of eggshell and other natural materials. This is useful for understanding how eggshell’s stiffness and toughness make it ideally suited to its purpose, and the mechanisms by which toughness is achieved.The paper also contains analysis of the effect of defect type, including cracks, notches and holes, to provide a fuller picture of defect tolerance which will be useful in the egg producing industry.