Inferior Tensile Properties Research Articles

Effect of fibre loading on mechanical properties of jute fibre bundle reinforced gypsum composites

Gypsum plasterboards are widely used in interior decoration like false ceilings, wall partitioning etc. The main component of this plasterboard is gypsum, which is a mineral material. These boards contain poor mechanical strength with lower durability. The addition of natural fibres in these plasterboards can be useful to achieve better mechanical properties. Since Jute fibre is abundant in Bangladesh and its usability in reinforced composites is well established, for this reason, jute fibre was selected to do the research. The aim of this study was to evaluate the impact of jute fibre on the mechanical properties of the gypsum plasterboard. To make this board, Plaster of Paris and water were thoroughly mixed to make a suspension first. Different fibre loadings of 2, 4, 6, and 8% were incorporated into gypsum composites. Reinforcement of 6% fibre provided the highest tensile properties, but 8% fibre loading showed inferior tensile and flexural properties. Impact test results showed a gradually improving nature with fibre loading, and hardness values showed a decreasing trend in hardness with higher fibre loading. FTIR results and SEM images confirmed that no significant chemical bonding took place in the composites, instead, the composite depended mainly on the mechanical bonding among the reins crystals and between the fibre and gypsum matrix.

Possible relationships between the physical conditions of cattle and the occurrence of structural modifications of their coat hair

Context Concerning the epithelial tissue in the skin, including hair, vitamin A is required for the integrity of epithelial cells, strengthened by compounding keratin fibres. Further, the complex hormonal changes seen in pregnancy may contribute to the hair growth. Thus, the structure of the cattle coat hair may change depending on the conditions of vitamin A deficiency or pregnancy. Aims The effects of several diseases, i.e. vitamin A deficiency, pneumonia, chronic pneumonia, and chronic renal failure, or pregnancy, on the structure of the coat hair were investigated. Methods Physical properties of the coat hair, collected from Japanese black cattle (Bos Taurus) and Holstein cows (Bos taurus Taurus), were investigated to study the effects of vitamin A deficiency, other diseases, or pregnancy on the formation of hair. Key results When vitamin A concentration was lowered to about half of the minimum concentration for vitamin A adequacy of 20 μg/dL in plasma (i.e. deficiency level was high), we could perceive the interference in the self-assembly of the keratin fibrils. However, we also confirmed structural modifications of the keratin fibres obtained from the cattle suffering chronic renal failure. The coat hair collected from the pregnant cows tended to show superior tensile strengths to those of the hair from the non-pregnant ones when compared at the same diameter level, although pregnancy might have increased cortisol affecting the hair follicle function. Further, from the X-ray diffraction measurements, the non-pregnant cow coat hairs, having exhibited the inferior tensile properties, were found to be structurally modified. Conclusions The structure of the coat hair could be modified when the vitamin A concentration was severely reduced (vitamin A deficiency). The physiological conditions during pregnancy may be advantageous to serve the regular formation of the hair. Implications Hair has a function serving as a proxy of health status for a certain period of animal life.

WC-reinforced iron matrix composites fabricated by wire arc additive manufacturing combined with gravity-driven powder feeding: particle transportation and size effects

Purpose A new wire arc additive manufacturing (WAAM) process combined with gravity-driven powder feeding was developed to fabricate components of tungsten carbide (WC)-reinforced iron matrix composites. The purpose of this study was to investigate the particle transportation mechanism during deposition and determine the effects of WC particle size on the microstructure and properties of the so-fabricated component. Design/methodology/approach Thin-walled samples were deposited by the new WAAM using two WC particles of different sizes. A series of in-depth investigations were conducted to reveal the differences in the macro morphology, microstructure, tensile performance and wear properties. Findings The results showed that inward convection and gravity were the main factors affecting WC transportation in the molten pool. Large WC particles have higher ability than small particles to penetrate into the molten pool and survive severe dissolution. Small WC particles were more likely to be completely dissolved around the top surface, forming a thicker region of reticulate (Fe, W)6C. Large WC particles can slow down the inward convection more, thereby leading to an increase in width and a decrease in the layer height of the weld bead. The mechanical properties and wear resistance significantly increased owing to reinforcement. Comparatively, samples with large WC particles showed inferior tensile properties owing to their higher susceptibility to cracks. Originality/value Fabricating metal matrix composites through the WAAM process is a novel concept that still requires further investigation. Apart from the self-designed gravity-driven powder feeding, the unique aspects of this study also include the revelation of the particle transportation mechanism of WC particles during deposition.

Synergy of tensile strength-ductility in IN718/CoCrFeMnNi/IN718 multi-material processed by powder high-pressure torsion and annealing

Materials manufactured through conventional powder metallurgy (PM) techniques generally exhibit inferior tensile properties due to structural defects. Nevertheless, a recently proposed cold-consolidation technique using powder high-pressure torsion represents well-manufactured structures with ultra-high tensile properties in the absence of cracks or pores. This novel PM-based technique is utilized in the present investigation to fabricate a multi-material Inconel 718/CoCrFeMnNi/Inconel 718 layered structure. By a combination of uttermost high densification, ultra-fine-grained microstructure, and hetero-deformation induced strengthening effect, the present cold-consolidated multi-material exhibits tensile properties with yield strength of 1255.4 MPa, uniform elongation of 13.7%, and total elongation of 25.0%, overcoming monolithic Inconel 718 and CoCrFeMnNi systems. These findings shed light on the capability of the cold-consolidation technique to manufacture multi-layered and gradient multi-functional structures with excellent mechanical response under tensile stress.

“In situ” compatibilization of poly(L-lactic acid)/epoxidized soybean oil bio-blends by reactive additives

Three reactive additives, i.e., dicumyl peroxide (DCP), styrene-glycidyl methacrylate oligomer (Joncry® ADR 4370 S) and 1, 4-phenyl diisocyanate (PDI), were used to compatibilize polyL-lactic acid (PLLA)/epoxidized soybean oil (ESO) bio-based blends via one-step melt blending. The bio-blends were characterized by means of Fourier transform infrared spectroscopy, field emission scanning electron microscopy, dynamic mechanical analysis, dynamic rheological analysis, thermogravimetric analysis, contact angle testing, differential scanning calorimetry and tensile testing. It is confirmed that the reactive additives interact with PLLA and ESO, and “in situ” graft copolymers are formed, which improves the interfacial compatibility. The stiffness of PLLA/ESO/additive bio-blends is greater than that of the PLLA/ESO blend, reflecting the enhanced interfacial adhesion between the PLLA and ESO phases. The melt viscosity and elasticity of the PLLA/ESO/4370 S and PLLA/ESO/PDI bio-blends are significantly improved, showing obvious non-Newtonian behaviors because of branched entanglements generated by chain extensions. However, the addition of DCP reduces the complex viscosity because the chain scissions destroy the macromolecular entanglements. The thermostability of the PLLA/ESO blend is decreased by the reactive additives. The surface hydrophobicity of PLLA/ESO/additive blends is improved due to the formation of branched grafts. The crystallinity of PLLA/ESO/additive bio-blends is increased because the “in situ” grafts serve as nucleating agents. The tensile strengths of the PLLA/ESO/4370 S and PLLA/ESO/PDI bio-blends are significantly increased due to the enhanced interface adhesion. The inferior tensile properties of the PLLA/ESO/DCP blends are ascribed to the degradation of the PLLA matrix. “In situ” reaction mechanisms for the compatibilized blends are proposed.

Tapioca starch/PVA plastic films with water hyacinth powder: Enhanced stability in direct contact with moisture

Thermoplastic starch/polyvinyl alcohol (TS/PVA) composite is high potential plastic material but its applications are restricted owing to its strong hydrophilicity. In this study, different amounts of cellulosic fibers in the form of powder were added to TS/PVA blend with the aim of slowing down the biodegradation rate of TS/PVA films in an environment with direct moisture contact. Water hyacinth as waste biomass is considered as a readily available and low-cost source of natural cellulosic fibers. Water hyacinth powder (WHp) was prepared from fresh water hyacinth leaves and petioles with bleaching as the only treatment carried out. TS/PVA films were prepared by sol–gel casting. A preliminary study revealed that the [7:20]-TS/PVA films containing 7% w/v of tapioca starch and 20% w/w (of starch dry weight) PVA are of highest potential in term of tensile properties. A series of [7:20/x]-TS/PVA/WHp films were prepared, where “x” refers to the percentage by weight of WHp (with respect to starch dry weight) added to the TS/PVA blend and ranges from 10, 15, 20 to 25%. It is found that, although the addition of WHp results in inferior tensile properties, the films’ elasticities are partially recovered when higher amount of WHp is added. Differential scanning calorimetry studies revealed that glass transition temperatures of the films with WHp additive is slightly higher than that of the film without the additive. The best tensile properties are observed in the [7:20/20]-TS/PVA/WHp films with the ultimate tensile strength of 14.20 ± 0.08 MPa. The resistances of the [7:20/x]-TS/PVA/WHp films to biodegradation in direct contact with moisture were assessed by burying in moisture-rich soil for weeks. All of the [7:20/x]-TS/PVA/WHp films are biodegradable but degrades at significantly slower rate than that observed in the [7:20]-TS/PVA films. The 2-week cumulative extent of biodegradation of the [7:20/20]-TS/PVA/WHp films reduces to 54.91%. From fabrication perspective, the incorporation of WHp at 20% w/w enhances the films’ stabilities against moisture to the greatest extent while retains usable elasticity for a range of applications.

Effect of rolling force on tensile properties of additively manufactured Inconel 718 at ambient and elevated temperatures

Inferior mechanical properties and severe anisotropy behavior of wire + arc additive manufactured (WAAM) Inconel 718 due to the large epitaxial grown columnar dendrites restrict the industrial application of WAAM deposition. Cold rolling was integrated into the WAAM deposition process and the effect of rolling force on microstructure, precipitatation distribution and tensile properties at ambient and elevated temperatures were investigated. The results show that the hardness of cold-rolled samples is much larger than that of the as-deposited and it increases with the increase in the rolling force. The columnar dendrites of the as-deposited sample changed to finer equiaxed grains of 26.5 and 14.7 µm after cold rolling with the force of 50 kN and 75 kN, respectively. Meanwhile, more uniformly distributed grains and less δ phase appear for 75 kN rolled sample. The stress-strain curves are smooth for the tensile tests at ambient temperature, while there are serrations at elevated temperature due to the dynamic strain aging behavior. The as-deposited sample shows inferior tensile properties to the wrought material at ambient and elevated temperatures. The cold-rolled samples both exceed the wrought material at ambient temperature; however, they show higher strength but lower elongation compared to the wrought material. The 75 kN cold rolled sample shows much higher strength and similar elongation to the wrought material for the test at elevated temperature. The grain morphology and recrystallization, as well as the strengthening mechanism of hybrid deposition and cold rolling process were discussed.

Quality Index Assessment of Multi-Pass Friction Stir Processed Al–Si–Mg Alloys Fully Produced by Recycling of Machining Chips

The capability of friction stir processing (FSP) in tensile properties/quality index enhancement of Al–Si–Mg alloys produced by 100% recycling of uncleaned and pre-cleaned machining chips was studied. Toward this end, FSP was applied on as-cast samples under the optimized parameters (rotation and traverse speeds of 2000 rpm and 12 mm/min). The results showed that the as-recycled samples show inferior tensile properties where the quality index of samples prepared by uncleaned chips (7.8 MPa) and pre-cleaned chips (33.7 MPa) is lower than that of sample prepared by virgin A356 ingot (300 MPa). Applying FSP substantially enhanced the tensile properties and quality index of the samples due to the microstructural modification/densification and the elimination of casting defects. For instance, the quality index of the four-pass FSPed recycled sample increased up to 43% compared to that of the as-cast A356 sample prepared by virgin ingots.

Characterisation of the tensile properties of Demineralised Cortical Bone when used as an anterior cruciate ligament allograft

BackgroundGraft choice in anterior cruciate ligament (ACL) reconstruction remains controversial and some grafts fail due to inadequate osteointegration. Demineralised cortical bone (DCB) is an osteoinductive collagen-based scaffold. The aim of this study was to measure the tensile properties of DCB from different locations and from different ages, and determine its compatibility with current ACL fixation systems. MethodsThe tensile properties of DCB manufactured from femur and tibia of young (9 month) and old (2–3 years) sheep was measured to determine the most appropriate graft choice. The ultimate load and stiffness of DCB allograft using two fixation systems, interference screws and sutures tied around screw posts, was measured ex vivo in an ovine ACL reconstruction model. Comparison was made with superficial digital flexor tendon (SDFT) and ovine ACL. ResultsDCB derived from young tibia had the highest ultimate load and stiffness of 67.7 ± 10.6 N and 130.2 ± 64.3 N/mm respectively. No DCB fixation system reached the published peak in vivo force through the ovine ACL of 150 N. SDFT fixation with interference screws (308.2 ± 87.3 N) did reach the in vivo threshold but was significantly weaker than ovine ACL (871.0 ± 64.2 N). ConclusionThe tensile properties of DCB were influenced by the donor age and bone. Owing to inferior tensile properties and incompatibility with suspensory fixation devices, this study indicates DCB is inferior to current tendon grafts options for ACL reconstruction.

Enhanced strength and ductility of Al0.9CoCrNi2.1 eutectic high entropy alloy by thermomechanical processing

Eutectic high entropy alloys (EHEAs) composed of soft face centered cubic (FCC) phase and hard body centered cubic (BCC) phases usually exhibit perfect combination of good tensile ductility and high fracture strength. Surprisingly, we reveal in this study that a new FCC(L12)/BCC(B2)-structured Al0.9CoCrNi2.1 EHEA shows inferior tensile properties with yield strength of 645 MPa, fracture strength of 1033 MPa and total elongation of merely 6.9%. A careful study of the deformation behavior reveals that the imperfect orientation relationship lead to extensive cleavage fracture and the consequent poor ductility. After thermomechanical treatment, a balanced and greatly enhanced tensile properties (yield strength of 820 MPa, fracture strength of 1400 MPa and total elongation of 11.6%) were achieved. The abnormal simultaneous enhancement for strength and ductility is resulted from the synchronous deformation of L12 and B2 phases. The current work presents a successfully demonstration of using thermomechanical processing to improve inferior mechanical properties of some lamellar eutectic alloys.

Integrated Extrusion–Shear Forming Process of the Solid-State Recycled AZ80 Magnesium Alloy via Hot Press Sintering

The consolidation recycled AZ80 billets were successfully fabricated through the cold press and hot press sintering of the AZ80 metal chips. The consolidation recycled billets sintered at 350 °C present the comparable compressive properties and inferior tensile properties compared with the initial cast billets. The defects in the consolidation recycled billet were inclined to propagate along the bond interface between the metal chips during tension, which resulted in the inferior tensile properties of the recycled billets. The recycled billets were then subjected to the integrated extrusion–shear (ES) process. The homogeneous finer dynamic recrystallization grains with an average grain size of 6 μm can be obtained in the shear deformation zone and extrusion sizing zone through integrated ES process at 300 °C with an extrusion velocity of 0.6 mm/s. The recycled billets after integrated ES forming process present rival tensile properties compared with the initial cast billets after integrated ES forming with the same extrusion parameters, which can be ascribed to that the integrated ES forming can nearly eliminate the defects through the severe compressive and shear strain. The solid-state recycling process through hot press sintering and subsequent integrated ES process can fabricate the consolidation recycled AZ80 rod, which demonstrates the comparable tensile properties with the cast–extrusion rod.

Study on Al/Mg/Al sheet fabricated by combination of porthole die co-extrusion and subsequent hot rolling

Al/Mg/Al sheet was fabricated by the proposed porthole die co-extrusion and subsequent hot rolling (PCE-R) method. The intermetallic compounds of β-Al3Mg2 and γ-Mg17Al12 were formed in transition layer after PCE-R process, and the thicknesses of β and γ layers became larger at higher rolling temperature or higher reduction ratio. Partial dynamic recrystallization (DRX) occurred in Al layer, and Al layer mainly consisted of shear-typed {111} fiber textures. However, if the rolling reduction is as high as 75%, Al layer exhibited quite different texture components. Mg layer consisted of fine equiaxed grains and several elongated grains, implying the occurrence of near complete DRX. With the increase of rolling temperature or reduction ratio, the number of Mg17Al12 particles in Mg layer was reduced, resulting into larger grain size. Mg layer had strong basal plane texture with c-axis parallel to transverse direction. Al/Mg/Al sheet rolled at 300 °C with 65% reduction exhibited two stress-drop fracture mechanism during tensile test, and it showed excellent tensile strength of 149 MPa, and elongation of 0.13. However, Al/Mg/Al sheet rolled with 75% reduction had inferior tensile properties due to the existence of some cracks after rolling.

Microstructure and mechanical properties of Mg-Al-Zn alloy extruded by porthole die with different initial billets

Porthole die extrusion of Mg-Al-Zn alloy was conducted using the as-cast, as-homogenized and as-extruded billets. The effects of initial microstructure on grain size, secondary particle, texture and mechanical properties of the extruded profiles were investigated. The results showed that complete dynamic recrystallization (DRX) occurred in welding zone of all profiles, and the profile extruded from as-cast billet had the smallest DRXed grains. Large un-DRXed grains with {10−12} extension twins were found in the matrix zone of the profiles extruded from as-cast and as-homogenized billets. In welding zone, all profiles have a strong basal plane texture with <0001> directions parallel to transverse direction, while the texture intensity and distribution significantly varied with initial billets. The profile obtained from as-extruded billet exhibited inferior tensile properties due to its low solid bonding degree. The hardness distribution in matrix zone of the profiles was not uniform due to the inhomogeneous microstructure.

Evaluation of Metal–Ceramic Composite Joint Under Tensile Loads at Elevated Temperature

An experimental study was undertaken to understand the tensile behavior of metal–ceramic composite joint with bolted configuration. Nickel based super alloy (GTM-Su-263) and SiCf/SiC composite were the material systems with an aerospace grade MJ6 bolt of GTM-Su-718. This bolted assembly was pulled at temperatures 25, 600 and 750 °C which were likely to be experienced in a typical aero engine. In case of metal–ceramic composite joint, the net tensile stress decreased from 110 to 88 MPa with increase in temperature from 25 to 600 °C. Similarly, the bearing stress reduced from 146 to 118 MPa. In all the metal–ceramic composite joints, the fracture initiated at the hole edge experienced the maximum tensile stresses. With further increase in temperature, reduction in the net tensile and bearing strength was significant and was attributed to the oxidation of the interface between the fiber and matrix. SEM studies clearly suggested that debonding and fiber pullout resulted in inferior tensile strength properties at elevated temperatures.

Deformation behavior in cold-rolled medium-manganese TRIP steel and effect of pre-strain on the Lüders bands

Deformation behavior was studied in cold-rolled 0.2C-1.6Al-6.1Mn-Fe transformation-induced plasticity (TRIP) steel subjected to intercritical annealing. The steel intercritically hardened at 650℃ exhibited excellent mechanical properties, and the excellent ductility was primarily associated with the discontinuous TRIP effect. Moreover at 650℃, the formation of Lüders bands was associated with TRIP effect and cooperative dislocation glide. The length of Lüders strain was gradually reduced with increasing pre-strain, and was eventually eliminated when the pre-strain was increased to 10%. The increased average stability of retained austenite and increased dislocation density in ferrite induced by pre-strain was responsible for decrease and ultimate elimination of Lüders bands. While in steel intercritically annealed at 600℃, ferrite and austenite was predominantly deformed, which was responsible for poor work hardening rate and inferior tensile properties.

A 9%Cr ODS steel composite material reinforced by Ti layers

In the present study, Ti toughened ODS (ODS/Ti) steels were researched. The effects of N on the formation of Ti(C,N) at the interface of ODS matrix and Ti layer and on the final toughening effect of ODS/Ti steels were studied. 0N, 0.2N-ODS/Ti steels all present inferior tensile properties that much lower than the strength and ductility of the corresponding pure ODS steels. While 0.5N-ODS/Ti steel exhibits extraordinary tensile strength of more than 2300MPa and strain of 13.5%. Elements interdiffusion across the interface of ODS and Ti layer causes the formation of detrimental intermetallic in Ti layer which leads to the inferior tensile properties of 0N-ODS/Ti and 0.2N-ODS/Ti steels. While the formation of a thick continuous Ti(C, N) layer at the interface of 0.5N-ODS matrix and Ti layer can limit the interdiffusion of elements and decrease the contents of brittle intermetallic. Besides, the Ti(C, N) formed at the interface which has intrinsic high strength and the high plasticity of Ti foil are assumed to have contributed to the extraordinary high strength and high ductility of 0.5N-ODS/Ti steel. The effect of multilayers’ interfaces on the toughening and strengthening mechanisms of layered ODS steel needs to be investigated at nano scale in the future.

Preparation and characterisation of luminous polypropylene/phosphor strontium aluminate nanocomposite fibres with enhanced dyeability

Phosphor strontium aluminate (SrAl2O4: Eu2+, Dy3+) nanoparticles, SAOED, were melt compounded with polypropylene on an internal mixer to prepare a uniform mixture with polymer and the resulting materials were granulated. PP/SAOED nanocomposite fibres were then produced by melt spinning method at the take-up speed of 1000 m min−1. Morphological, thermal, structural and luminescent properties of the luminous fibres were studied by SEM, differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and fluorescence spectrophotometer. The luminous fibres were then knitted and dyed to investigate the effects of SAOED nanoparticles on the dyeability of fibres. SEM results showed that with increasing SAOED nanoparticle amounts, the agglomerates of SAOED nanoparticles were appeared on the fibre surface. DSC results indicated that the SAOED nanoparticles did not affect melting and crystallisation behaviours significantly. WAXD patterns revealed that the crystal type of luminous nanocomposite fibres did not change and was still the α-monoclinic crystal form. The luminous nanocomposite fibres were found to have inferior tensile properties as compared to the neat PP fibre. From fluorescence spectrophotometer results, it can be seen that fibres excited at the wavelength of 400 nm, showed an emission peak at 550 nm and had green light. With increasing the amount of SAOED nanoparticles in the fibres, emission peak intensity of luminous fibres increased and also the fabric dyeability was improved.

Effect of high temperature ageing on microstructure and mechanical properties of a nickel-free high nitrogen austenitic stainless steel

The effect of ageing and oxidation at 850°C for different durations viz., 1, 10, 100 and 200h on microstructure and mechanical properties of a nickel free high nitrogen steel (Fe–Cr–Mn–N) was investigated. The microstructure of the alloy in as-received condition essentially consists of fine equi-axed austenite grains with annealing twins. However, ageing at 850°C has resulted in the formation of very fine, globular and discrete Cr2N precipitates initially at grain boundaries for an ageing time of 1h and subsequently within the grains with increasing ageing time beyond 1h. The size of these precipitates has progressively increased with further ageing. In addition, coarse intermetallic precipitates of (Fe,Mn)Cr type with body centred tetragonal structure were observed in the samples aged for ≥100h at 850°C. The effect of these precipitates on mechanical properties of the alloy was studied. It was noticed that the mechanical properties deteriorated on ageing, which has been attributed to the depletion of solid solution strengthening elements like nitrogen, chromium and manganese from the matrix to form nitrides and intermetallic precipitates. Moreover the alloy aged in air (i.e., oxidised) exhibits marginally inferior tensile properties as compared to unoxidised alloy.

Preparation and characterization of nanocomposites of poly-p-phenylene benzobisthiazole with graphene nanosheets

Poly-p-phenylene benzobisthiazole (PBT)/graphene nanocomposite films were fabricated using a simple method with methanesulfonic acid (MSA) as the processing solvent. In this approach, graphene nanosheets were exfoliated in the MSA solution of PBT using ultrasonication and mechanical stirring, and then processed into thin films. The structure and composition of as-prepared graphene oxide (GO) and reduced graphene oxides (rGO) were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrical conductivity of pristine PBT was enhanced by 10 orders of magnitude upon incorporation of 5 wt% rGO nanosheets. The enhanced conductivity of the nanocomposites was interpreted by the percolation model. The thermo-oxidative stability of PBT was improved with the incorporation of both GO and rGOs, while rGOs showed more pronounced effect. On addition of only 5 wt% GO, the tensile strength and Young's modulus of PBT increased by ∼4-fold and ∼7-fold, respectively, whereas relatively inferior tensile properties were observed for the PBT/rGO nanocomposites. The enhanced mechanical properties could be attributed to the molecular-level dispersion of the exfoliated GO nanosheets in PBT matrix, as evidenced by the results from morphological studies. A modified Halpin–Tsai model has been used to evaluate the reinforcement or orientation effects of GO/rGO on the Young's modulus of the nanocomposites.

Mammalian cortical bone in tension is non-Haversian.

Cortical bone, found in the central part of long bones like femur, is known to adapt to local mechanical stresses. This adaptation has been linked exclusively with Haversian remodelling involving bone resorption and formation of secondary osteons. Compared to primary/plexiform bone, the Haversian bone has lower stiffness, fatigue strength and fracture toughness, raising the question why nature prefers an adaptation that is detrimental to bone's primary function of bearing mechanical stresses. Here, we show that in the goat femur, Haversian remodelling occurs only at locations of high compressive stresses. At locations corresponding to high tensile stresses, we observe a microstructure that is non-Haversian. Compared with primary/plexiform bone, this microstructure's mineralisation is significantly higher with a distinctly different spatial pattern. Thus, the Haversian structure is an adaptation only to high compressive stresses rendering its inferior tensile properties irrelevant as the regions with high tensile stresses have a non-Haversian, apparently primary microstructure.