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Fracture mode control: a bio-inspired strategy to combat catastrophic damage.

Yao H, Xie Z, He C, Dao M - Sci Rep (2015)

Bottom Line: Recent studies on biomaterials have revealed that many structural biomaterials tend to be fractured, under sufficiently high indentation load, through ring cracking which is more localized and hence less destructive compared to the radial one.Many structural biomaterials in nature are found to have modulus mismatch close to the CMM.Our results not only shed light on the mechanics of inclination to ring cracking exhibited by structural biomaterials but are of great value to the design of laminated structures with better persistence of structural integrity.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China.

ABSTRACT
The excellent mechanical properties of natural biomaterials have attracted intense attention from researchers with focus on the strengthening and toughening mechanisms. Nevertheless, no material is unconquerable under sufficiently high load. If fracture is unavoidable, constraining the damage scope turns to be a practical way to preserve the integrity of the whole structure. Recent studies on biomaterials have revealed that many structural biomaterials tend to be fractured, under sufficiently high indentation load, through ring cracking which is more localized and hence less destructive compared to the radial one. Inspired by this observation, here we explore the factors affecting the fracture mode of structural biomaterials idealized as laminated materials. Our results suggest that fracture mode of laminated materials depends on the coating/substrate modulus mismatch and the indenter size. A map of fracture mode is developed, showing a critical modulus mismatch (CMM), below which ring cracking dominates irrespective of the indenter size. Many structural biomaterials in nature are found to have modulus mismatch close to the CMM. Our results not only shed light on the mechanics of inclination to ring cracking exhibited by structural biomaterials but are of great value to the design of laminated structures with better persistence of structural integrity.

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Effect of gradient transition layer on the CMM.In the gradient transition layer, the Young's modulus is assumed to vary from the modulus of the coating to that of the substrate in a linear way. Here tgrad and t stand for the thicknesses of gradient layer and coating respectively. Poisson's ratios are consistently taken as 0.3.
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f7: Effect of gradient transition layer on the CMM.In the gradient transition layer, the Young's modulus is assumed to vary from the modulus of the coating to that of the substrate in a linear way. Here tgrad and t stand for the thicknesses of gradient layer and coating respectively. Poisson's ratios are consistently taken as 0.3.

Mentions: For the laminated biomaterials in nature, it may not be easy to obtain the precise Poisson's ratio for each layer and then to predict the corresponding CMM. However, if we take 0.1–0.4 as the reasonable range of Poisson's ratio of biomaterials, the CMM of natural laminated biomaterials, in the light of Fig. 6a, is estimated ranging from 1.0 to 3.3. It is interesting to compare this theoretical prediction with the measured value. Table 1 listed the modulus mismatch of some laminated biomaterials reported in literature. The inclination to ring cracking has been confirmed in some of these materials such as the scale of Polypterus senegalus being bitten by its predator's teeth1. It is interesting to notice that the measured modulus mismatch of the listed biomaterials range from 0.93 to 3.6, overlapping the range of the CMM calculated above. However, for a particular case such as the teeth of Mylopharyngodon piceus19, if the Poisson's ratios of the coating (enameloid) and substrate (dentine) are both taken as 0.3, the CMM is estimated to be around 1.6, which is lower than the measured modulus mismatch 3.5 as shown in Table 1. Such discrepancy may result from our negligence of more specific features in our modeling above. For example, in our previous analysis, we assumed that the modulus across the coating/substrate interface is discontinuous. In fact, transitional interlayer with graded properties is often observed between distinct layers in natural laminated biomaterials. Such gradient interlayer has been demonstrated to play an important role in mitigating the stress and strain concentration at the interface118. The effect of gradient transition layer on the CMM is studied by using finite element analysis (Supplementary Information). Fig. 7 shows the calculated fracture mode maps for the cases with gradient interlayer of thickness tgrad in comparison to those without interlayer. It can be seen that the radial cracking regime shrinks and the CMM increases after introducing the gradient interlayer between the coating and substrate. The thicker the interlayer, the higher the CMM. For the teeth of Mylopharyngodon piceus, the reduced modulus obtained by nano-indentation exhibits gradient in the vicinity of the enameloid/dentine interface19. Assuming that the thickness of the gradient interlayer is equal to the coating (enameloid layer) thickness, Fig. 7 implies that the CMM could rise up to 3.5, which agrees well with its measured value.


Fracture mode control: a bio-inspired strategy to combat catastrophic damage.

Yao H, Xie Z, He C, Dao M - Sci Rep (2015)

Effect of gradient transition layer on the CMM.In the gradient transition layer, the Young's modulus is assumed to vary from the modulus of the coating to that of the substrate in a linear way. Here tgrad and t stand for the thicknesses of gradient layer and coating respectively. Poisson's ratios are consistently taken as 0.3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4306140&req=5

f7: Effect of gradient transition layer on the CMM.In the gradient transition layer, the Young's modulus is assumed to vary from the modulus of the coating to that of the substrate in a linear way. Here tgrad and t stand for the thicknesses of gradient layer and coating respectively. Poisson's ratios are consistently taken as 0.3.
Mentions: For the laminated biomaterials in nature, it may not be easy to obtain the precise Poisson's ratio for each layer and then to predict the corresponding CMM. However, if we take 0.1–0.4 as the reasonable range of Poisson's ratio of biomaterials, the CMM of natural laminated biomaterials, in the light of Fig. 6a, is estimated ranging from 1.0 to 3.3. It is interesting to compare this theoretical prediction with the measured value. Table 1 listed the modulus mismatch of some laminated biomaterials reported in literature. The inclination to ring cracking has been confirmed in some of these materials such as the scale of Polypterus senegalus being bitten by its predator's teeth1. It is interesting to notice that the measured modulus mismatch of the listed biomaterials range from 0.93 to 3.6, overlapping the range of the CMM calculated above. However, for a particular case such as the teeth of Mylopharyngodon piceus19, if the Poisson's ratios of the coating (enameloid) and substrate (dentine) are both taken as 0.3, the CMM is estimated to be around 1.6, which is lower than the measured modulus mismatch 3.5 as shown in Table 1. Such discrepancy may result from our negligence of more specific features in our modeling above. For example, in our previous analysis, we assumed that the modulus across the coating/substrate interface is discontinuous. In fact, transitional interlayer with graded properties is often observed between distinct layers in natural laminated biomaterials. Such gradient interlayer has been demonstrated to play an important role in mitigating the stress and strain concentration at the interface118. The effect of gradient transition layer on the CMM is studied by using finite element analysis (Supplementary Information). Fig. 7 shows the calculated fracture mode maps for the cases with gradient interlayer of thickness tgrad in comparison to those without interlayer. It can be seen that the radial cracking regime shrinks and the CMM increases after introducing the gradient interlayer between the coating and substrate. The thicker the interlayer, the higher the CMM. For the teeth of Mylopharyngodon piceus, the reduced modulus obtained by nano-indentation exhibits gradient in the vicinity of the enameloid/dentine interface19. Assuming that the thickness of the gradient interlayer is equal to the coating (enameloid layer) thickness, Fig. 7 implies that the CMM could rise up to 3.5, which agrees well with its measured value.

Bottom Line: Recent studies on biomaterials have revealed that many structural biomaterials tend to be fractured, under sufficiently high indentation load, through ring cracking which is more localized and hence less destructive compared to the radial one.Many structural biomaterials in nature are found to have modulus mismatch close to the CMM.Our results not only shed light on the mechanics of inclination to ring cracking exhibited by structural biomaterials but are of great value to the design of laminated structures with better persistence of structural integrity.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China.

ABSTRACT
The excellent mechanical properties of natural biomaterials have attracted intense attention from researchers with focus on the strengthening and toughening mechanisms. Nevertheless, no material is unconquerable under sufficiently high load. If fracture is unavoidable, constraining the damage scope turns to be a practical way to preserve the integrity of the whole structure. Recent studies on biomaterials have revealed that many structural biomaterials tend to be fractured, under sufficiently high indentation load, through ring cracking which is more localized and hence less destructive compared to the radial one. Inspired by this observation, here we explore the factors affecting the fracture mode of structural biomaterials idealized as laminated materials. Our results suggest that fracture mode of laminated materials depends on the coating/substrate modulus mismatch and the indenter size. A map of fracture mode is developed, showing a critical modulus mismatch (CMM), below which ring cracking dominates irrespective of the indenter size. Many structural biomaterials in nature are found to have modulus mismatch close to the CMM. Our results not only shed light on the mechanics of inclination to ring cracking exhibited by structural biomaterials but are of great value to the design of laminated structures with better persistence of structural integrity.

Show MeSH
Related in: MedlinePlus