•Interweaving lattices formed by spicules on the skeletal wall of Euplectella aspergillum increases the number of free nodes and makes the structure flexible.•The varying cross-sectional area of ...individual spicules have a profound effect on their tensile and fracture behavior.•The layered architecture profoundly affects the fracture process by inducing multiple toughening mechanisms.•Spicule failure starts from the outer layers and proceeds through these layers to the center core.
The extraordinary mechanical properties shown by many biological materials stem from their unique hierarchical structures. The spicules of the deep-sea glass sponge, Euplectella aspergillum, show layered architecture and are known to improve toughness in various loading conditions. In the present work, we conducted a systematic study on the tensile and fracture behavior of E. aspergillum’s spicules. Tensile tests were performed on three different gage lengths of spicules that compose anchoring structures of E. aspergillum. The cross-sectional area of each spicule was accurately measured using an x-ray microscope. The effect of gage length and varying cross-sectional area on the tensile behavior of spicules is discussed in detail. The interplay between two failure initiation sites, namely, weakest-link flaws and minimum cross-sectional area locations was observed. Weibull statistics were used to quantify the variability in the strengths of spicules as a function of their gage length. The Weibull modulus was observed to decrease with the increase in gage length. The possibility of a bimodal flaw population for a higher gage length of spicules due to the interplay between failure initiation sites is also discussed. The fractography study was utilized to understand the failure and toughening mechanisms of spicules in tensile loading. The fracture toughness of the central core was quantified from fracture surfaces using a linear elastic fracture mechanics model. The present study shows that the failure of spicules initiates in the outer layers and proceeds progressively to the center. The layers surrounding the central core of the spicule resist the crack propagation and increase its toughness.
Scaling up the cold sintering process of ceramics Jabr, Abdullah; Jones, Haley N.; Argüelles, Andrea P. ...
Journal of the European Ceramic Society,
September 2023, 2023-09-00, Volume:
43, Issue:
12
Journal Article
Peer reviewed
Open access
The cold sintering process (CSP) densifies ceramics below 300 °C by utilizing a transient phase and applied pressure. Although CSP has been employed for densifying a variety of functional systems, ...their structural integrity does not always reach that of conventionally sintered parts. On the example of ZnO, this study aims to eliminate processing-induced defects that compromise the strength of cold sintered materials. Ultrasonic evaluation was employed for nondestructive detection of flaws prior to mechanical testing. Load transfer misalignments and fast heating rates were found as major sources of defects, impairing the mechanical strength. Based on these findings, multiple disc-shaped samples (13 mm diameter and ∼1.3 mm thickness) were cold sintered simultaneously using precisely aligned punches and slow heating rates. The obtained homogeneous densification, high relative density (>97%) and relatively high strength (∼120 MPa), i.e. two times superior to previously reported values, demonstrates the feasibility of scaling up the CSP towards industrial implementation.
Components manufactured by laser powder bed fusion (LPBF) are limited by their performance for use in critical applications. LPBF materials have microstructural defects, such as suboptimal grain size ...and morphology, and macroscale anomalies, such as lack of fusion. This results in LPBF components performing below their wrought counterparts for various mechanical properties, such as creep which has seldom been researched. To understand the creep behaviour of LPBF alloy 718, parts were fabricated using different scanning strategies and build orientations and creep tested at 650 °C under a 600 MPa load. Heat treatment increased the creep life by a factor of 5, confirming its necessity. The build orientation and stress state were shown to be determining factors in the creep failure mechanisms. The Meander scanning strategy resulted in a 58% increase in creep life compared to the Stripe strategy, due to the detrimental effects of the numerous laser overlapping regions in the Stripe strategy. For a given strategy, a 24% increase in creep life compared to wrought alloy 718 was observed, indicating that LPBF has the potential to surpass wrought material properties. As a result of this work, it is possible to propose build strategies for high temperature creep applications.
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•An additively built specimen obtained a similar creep rate and a 24% longer creep life than wrought alloy 718.•The build orientation and stress state of the specimens are responsible for the specimens' different failure modes.•The Stripe strategy has numerous laser overlapping areas which cause poorer creep properties than the Meander strategy.•δ-precipitates are key for creep performance as they impede microvoid coalescence and slow the creep rate.
In this work, we demonstrate for the first time that the inherent low performance to out-of-plane loading of thin-ply Carbon Fibre Reinforced Plastics (CFRPs) can be overcome with tailored ...bio-inspired Bouligand microstructures. To this end, we designed, manufactured ultra-thin-ply CFRP Bouligand laminates and conducted an original study which combines full-penetration quasi-static indentation tests, in situ three-point bending tests conducted under a SEM and detailed analytical modelling. We investigated a wide range of mismatch (pitch) angles 2.5°, 5°, 10°, 20°, 45°, showing that decreasing pitch angles simultaneously achieved a larger (i) load-bearing capability, (ii) delay in catastrophic failure and (iii) total dissipated energy. We then investigated the role of the pitch angle on the activation of the highly dissipative sub-critical failure mechanisms responsible for the high mechanical performances achieved by small pitch angles laminates. Our investigation clearly shows that, with ultra-thin-ply CFRP, smaller pitch angles achieve higher damage tolerance and structural integrity.
Highlights • Veneer chipping was the prominent fracture mode in clinically retrieved zirconia–ceramic and metal–ceramic fixed dental prostheses. • All fracture initiated at the occlusal wear facets. ...• Zirconia–ceramic exhibited a higher rate of veneer fracture with larger chip sizes relative to their metal–ceramic counterparts.
Deformation, damage and wear characteristics of spark plasma sintered VC, NbC and ZrC refractory carbides have been investigated using nanoindentation, tribology and micro/macro − indentation tests. ...Fractography, using SEM, AFM and confocal microscopy, was used for the characterization of deformation and damage mechanisms. Considerable indentation load − size effect was found in all systems with hardness values from 30 to 36GPa to 13–17GPa corresponding to the applied loads of 1 mN and 100N, respectively. During nanoindentation, characteristic stress-drops were observed on hardness-displacement profiles of NbC and ZrC at depth region of 15–30nm while this was not typical in VC. The highest coefficient of friction was measured for NbC with a value of 0.45 and the lowest for ZrC with an average value of 0.3. The wear rate of the NbC, and VC was similar, approximately 3×10−6mm3/Nm only the wear rate of ZrC was larger, approximately 2×10−5mm3/Nm.
This study focuses on the failure analysis of woven fabric carbon-reinforced polymeric composites under tensile and flexural loading. To conduct a detailed investigation acoustic emission is used to ...attain damage evolution under flexural loading conditions. For the first time, the GAP function is suggested to find the optimal number of clusters for acoustic emission data. The advantage of this function is its suitability for classifying elongated data points in the vector space of acoustic data. Three clusters of data are determined with this new approach, indicating various failure types in composite laminates which show that simultaneous occurrence of all failures results in a major change of material stiffness. These failures are also substantiated by scanning electron microscope studies of fracture surfaces. Further studies on tensile behavior of the same laminates are conducted with the help of scanning electron micrographs and 3D-digital image correlation technique. Remarkably, the presence of the shear and transverse strain fields at the surface of the tensile specimen obtained through the digital image correlation technique can be correlated to shear dominant and high energy failure (interlaminar delamination and fiber pull-outs), respectively, which are also confirmed by microscopic images of the same fracture regions.
Al3Ti reinforced Aluminium composites with different weight percent of Al3Ti particles were developed by in-situ reaction of aluminium alloy with potassium hexafluorotitanate (K2TiF6). ...Ultrasonication of the aluminium melt during salt reaction was carried out to refine the cast microstructure and achieve better dispersion of in-situ formed Al3Ti particles. The in-situ composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Al3Ti particles generated in the melt promoted heterogeneous nucleation, which was responsible for grain refinement of the cast microstructure. The well dispersed Al3Ti significantly improved the mechanical properties including ductility, yield strength (YS), ultimate tensile strength (UTS) and hardness. The dominant strengthening mechanism in the composite was the thermal mismatch strengthening followed by Hall-Petch strengthening.
•Homogeneous and fine dispersion of Al3Ti in the aluminium matrix is achieved due to ultrasonic stirring.•Al3Ti particles act as heterogeneous nucleation sites and refine the cast microstructure.•TEM analysis confirmed that the interface between Al3Ti particles and Al matrix was clean and well bonded.•Better mechanical properties (hardness, yield strength, UTS and % elongation) are reported for the composites.•Thermal mismatch strengthening was found to be the dominant strengthening mechanism of the composite.
•Hydrogen embrittlement (HE) studied with permeation and novel tuning-fork testing (TFT)•Compact in situ TFT links stress with time to initiation/fracture, and with crack propagation rate.•Enhanced ...HE resistance with elongated PAGs in specific propagation direction.•Crack propagation mechanism (intergranular/quasi-cleavage) depends on PAG shape.•No correlation between fourfold PAG surface area difference and H diffusion.
Suppressing hydrogen embrittlement in martensitic steels is a longstanding challenge. Here, we studied the effects of prior austenite grain (PAG) shape and size with a 0.25C steel utilising novelin situH-charging, constant-displacement Tuning-fork testing (TFT) and H-permeation tests. Anisotropic elongated PAG structure has enhanced HE resistance transverse to the rolling direction (RD) with slower crack propagation rate (CPR) and quasi-cleavage fracture. Larger elongated grains are prone to intergranular fracture when crack propagates in RD. Reaustenitised equiaxed PAGs fail with intergranular cracking, which accelerates max CPR up to threefold compared to quasi-cleavage. All the microstructures have similar H-diffusion ∼5 × 10−7 cm2/s and density of reversible H-traps NT ∼ 3 × 1016, irrespective of PAG surface area, indicating that PAG boundaries are not effective diffusion paths. Deformed PAG boundaries mitigate susceptibility to intergranular cracking.
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