Bulk Strength Research Articles

Additive Manufacturing, Numerical and Experimental Analyses for Pentamode Metamaterials

Pentamodes are lattice structures composed of beams. Their main property is the low ratio of the shear to bulk modulus, making them suitable for aerospace, antiseismic, and bioengineering applications. At first, in our study, pentamode structures were fabricated using three-dimensional printing and were tested in a laboratory. Then, computational analyses of bulk strength have been performed. In addition, several preliminary computational analyses have been considered, comparing different pentamodes’ dimensions and topologies in order to understand their behaviour under different loading conditions. Experimental results have been compared with the numerical results in order to validate the forces applied to the lattice structures. Our new contribution is that for the first time, the experimental and numerical results are investigated up to the failure of the specimens, the effective Young’s modulus has been calculated for different pentamode lattice structures, and our results are also compared with analytical equations.

Mild Fabrication of Polymeric Porous/Nonporous Micro‐Composite Structures via Enhancing the Photothermal Conversion of Ultrafast Laser

AbstractLocalized foaming of polymers is promising to fabricate polymeric composite structures for applications in biomedical, aerospace, automotive, etc. However, the severe pyrolysis and carbonization of polymer chains during localized foaming may degrade the bulk strength. Herein, a mild localized foaming strategy is proposed to fabricate poly(lactic acid) (PLA) micro‐foams within dense PLA matrices using ultrafast lasers. The PLA substrates doped with graphene (Gr) and azodicarbonamide (AC) are developed for mild foaming. A picosecond laser is applied to pattern PLA micro‐foams on the PLA/Gr/AC substrates to fabricate porous/nonporous micro‐composite structures. The thermal behavior of the PLA/Gr/AC substrates is characterized to evaluate their capability in photothermal conversion and mild foaming during ultrafast laser pulses. To optimize the laser foaming process, the microstructure of the laser‐foamed PLA processed with different laser parameters is studied. It demonstrates that the oxidation of the functional groups dominates the side reactions on the PLA chains with slight variation in molecular weight during laser foaming, indicating that the PLA chains keep almost intact and mild localized foaming is realized. Furthermore, the developed technology is demonstrated for micro‐patterning and texturing, material toughness programming, and shape memory programming, showing promising applications for smart materials, metamaterials, micro‐robotics, and biological scaffolds.

Comparing microstructure and mechanical properties of AlSi10 alloy produced by powder bed fusion-laser beam and high pressure die casting

PurposePowder bed fusion-laser beam (PBF-LB) is a rapidly growing manufacturing technology for producing Al-Si alloys. This technology can be used to produce high-pressure die-casting (HPDC) prototypes. The purpose of this paper is to understand the similarities and differences in the microstructures and properties of PBF-LB and HPDC alloys.Design/methodology/approachPBF-LB AlSi10Mg and HPDC AlSi10Mn plates with different thicknesses were manufactured. Iso-thermal heat treatment was conducted on PBF-LB bending plates. A detailed meso-micro-nanostructure analysis was performed. Tensile, bending and microhardness tests were conducted on both alloys.FindingsThe PBF-LB skin was highly textured and softer than its core, opposite to what is observed in the HPDC alloy. Increasing sample thickness increased the bulk strength for the PBF-LB alloy, contrasting with the decrease for the HPDC alloy. In addition, the tolerance to fracture initiation during bending deformation is greater for the HPDC material, probably due to its stronger skin region.Practical implicationsThis knowledge is crucial to understand how geometry of parts may affect the properties of PBF-LB components. In particular, understanding the role of geometry is important when using PBF-LB as a HPDC prototype.Originality/valueThis is the first comprehensive meso-micro-nanostructure comparison of both PBF-LB and HPDC alloys from the millimetre to nanometre scale reported to date that also considers variations in the skin versus core microstructure and mechanical properties.

Barnacle-inspired amphipathic high strength adhesives under-water/oil

Adhesives designed for bonding in liquid environments have a broad application prospect. In general, amphiphilic polymer structures are important research objects for underwater bonding. And in the study of underwater adhesives, it was found that they can quickly dispel or absorb interfacial water and form reliable bulk strength and adhesion strength. However, achieving strong adhesion in both water-based and oily environments poses a significant challenge. In this work, an adhesive inspired by barnacles that can meet the bonding requirements in both water-based and oily environments has been prepared. Hydrophilic (polyethylene glycol (PEG)) main chains and hydrophobic (1-Octadecyl thiol (ODT)) side chains are simultaneously integrated into the polyurethane structure. Different from the past, hydrophobic and hydrophilic segments are included in the hard segment and soft segment microregion, respectively; At the same time, both hydrophilic and hydrophobic chain segments have strong crystallization, which greatly strengthens the driving force of molecular segments migration and phase separation compared with ordinary hydrophilic/hydrophobic structures. Water-based and oil-based solvents drive hydrophilic and hydrophobic molecular chains to diffuse to the surface, respectively, which enhances the adhesive strength to hydrophilic and hydrophilic surfaces, respectively. In comparison to the adhesion strength observed in air, the adhesion strength of the adhesive to polymethyl methacrylate (PMMA) increases by 1.72 times in oil environments (from 1.02 to 1.75 MPa). Similarly, the adhesion strength to aluminum (Al) increases by 2.23 times under water (from 1.82 to 4.04 MPa). These findings suggest that the regulation strategy for polymer chains employed in this study holds great potential for advancing adhesive performance in diverse environments.

Arginine-solubilized lipoic acid-induced β-sheets of silk fibroin-strengthened hydrogel for postoperative rehabilitation of breast cancer

Breast cancer is the most common cancer among women worldwide, and adjuvant radiotherapy (RT) following tumor removal is one of the most commonly used treatments for breast cancer. However, the high risk of tumor recurrence and inevitable radiation skin injury after RT remain fatal problems, seriously challenging the patient's postoperative rehabilitation. Herein, a multifunctional poly (lipoic acid)-based hydrogel is constructed through one-step heating the mixture of α-lipoic acid (LA)/arginine (Arg)/silk fibroin (SF), without introducing any non-natural molecules. The multiple synergistic interactions among LA, Arg, and SF not only enhance the solubilization of LA in aqueous systems but also stabilize poly(lipoic acid) through strong salt bridge hydrogen bonds and ionic hydrogen bonds. Intriguingly, the LA-based surfactant induced β-sheet transformation of SF can further modulate the bulk strength of the hydrogel. Regulating the content of LA in hydrogels not only allows efficient control of hydrogel bioactivity but also enables the evolution of hydrogels from injectable forms to adhesive patches. Based on the different biological activities and forms of hydrogels, they can be implanted internally or applied externally on the mice's skin, achieving simultaneous prevention of tumor recurrence post-surgery and assistance in treating radiation-induced skin damage after radiotherapy.

Investigation of geometric and material effects on the fatigue performance of composite and steel adhesive joints

This study experimentally investigates the combined effect of several parameters on the fatigue behaviour of adhesive bonded single lap joints, including: substrate material (steel, glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP)); adhesive material (epoxy and methacrylate); as well as joint geometry (overlap length and adhesive thickness).Results showed that despite the lower bulk strength of the ductile methacrylate adhesive, in terms of the ratio of fatigue load to ultimate failure load, joints bonded by this adhesive had a higher fatigue performance when compared to joints bonded by the epoxy one, with differences in fatigue life of up to 20 times for the same load ratio. In a similar substrate configuration, flexible GFRP substrates reduced the fatigue life of the joints bonded by the methacrylate adhesive more than 10 times when compared to steel joints for the same load. However, in a dissimilar configuration, an increase in fatigue life was observed which, based on a finite element analysis, was attributed to the ductility of the adhesive and its effects on the stress field. In CFRP joints bonded by the epoxy adhesive, a deterioration in fatigue performance was observed due to the occurrence of interfacial failure.Regarding the geometrical factors, increasing overlap length led to a decrease of the fatigue life for the same nominal shear stress. Similar trend was obtained for adhesive thickness. A parametric analysis revealed that overlap length is the parameter that affects more the fatigue performance of the joints.

Study of rock fracture patterns for obtaining the basis for energy-efficient ore ball milling

The study is conducted using methods of analysis (in proving the possibility of assessing the disintegration of rocks by energy consumption), methods of free vibration theory (to determine the motion of a falling ball over an elastic connection), methods of energy balance, methods of theoretical mechanics and material resistance (to study amplitude characteristics of mechanical systems), methods of rock fracture theory (to determine fracture work), physical modeling (to design test benches) and experimental methods (to find relationships between parameters). The strength of bulk crushed material in the first stages of ore preparation is practically independent of its coarseness and solid form, which allows the estimated volume of disintegrated ore (particle concentration) to be determined by the energy expended, translated into other physical quantities. Results of experimental studies support the theoretical dependences. The proposed approach of automatic stabilisation of solid concentration in the ball mill pulp at the optimum level allows to increase the productivity of ore preparation on the finished grade in the first stages by 10% at reduction of specific power consumption for ore grinding.

Stiffness, strength, anisotropy, and buckling of lattices derived from TPMS and Platonic and Archimedean solids

Lattice metamaterials have gained considerable attention due to their distinctive topological structures and multifunctional properties. In this work, the effect of topology, loading conditions, and relative density on the effective mechanical properties of various novel lattice architectures is investigated numerically and experimentally. Thirteen strut-based lattices derived from triply periodic minimal surfaces (five lattices) as well as Platonic (three lattices) and Archimedean (five lattices) solids are considered for the first time, and their anisotropic mechanical properties, including uniaxial, shear, and bulk moduli and strengths as well as their total stiffness, buckling strengths, Poisson’s ratio, and anisotropy are investigated as a function of a wide range of relative densities (0.1% to 37%). Finite element analysis is employed to capture the full effective behavior of these lattices using periodic boundary conditions. Bifurcation analysis is performed to predict the threshold relative density governing their buckling vs yielding deformation behavior. Selected lattice structures of various relative densities are 3D printed using polymer selective laser sintering additive manufacturing technique and tested under quasi-static uniaxial compression where the experimental and numerical results are compared. The numerical results indicate that the deformation behavior can be altered between stretching and bending dominated mode of deformation as function of loading. Archimedean lattices are shown to outperform a wide range of strut-based lattices. This work opens the doors for more investigations of the multifunctional properties of these novel types of lattices and their engineering applications. Furthermore, the generated comprehensive data are useful in optimizing latticed structures using topology optimization techniques.

Performance of low-cost fiber optic cables as leak detection sensors for water pipelines in unsaturated soil

Large volumes of potable water are lost from leaks in water distribution systems around the world. Such leaks may go undetected for a long time. A passive means of leak detection can be implemented by burying a suitable fiber optic cable in the pipe trench with water distribution pipes when they are installed. Water leaking from pipes into the ground results in a temperature change at the leak location. Leaks into unsaturated soil also cause changes in the bulk density and strength of the soil, resulting in significant soil deformation. Brillouin Frequency Shift (BFS) in optical fibers is sensitive to changes in both temperature and mechanical strain, allowing fiber optic cables to act as efficient leak detection sensors. Purpose-made fiber optic cables may be expensive, but telecommunication grade cables generally have a low cost and are readily available around the world. This paper investigates the performance of five different fiber optic cables, including communication grade fiber optic cables, to act as leak detection sensors in unsaturated ground. It was found that the most efficient leak detection sensors are flexible tight-buffered fiber optic cables.

Trace nano-Ti addition for graphene nanoplatelets/copper composites to simultaneously enhance strength-ductility and wear resistance

Graphene nanoplatelets (GNPs)/copper composites containing nano-Ti addition were prepared using the vacuum hot-pressing sintering process. The effect of Nano-Ti on microstructure and mechanical properties of GNPs/copper composite was investigated. Before the sintering of the composite powders, the massive nano-Ti particles decorated on the GNPs surface. The GNPs/Ti chemical reaction occurred during the sintering, and then formed abundant TiC particles. Hardness and strength of bulk GNPs/copper composites were enhanced evidently by nano-Ti addition, which increased with nano-Ti increasing. The nano-Ti addition achieved simultaneous strength-ductility enhancement of GNPs/copper composites. The hardness, tensile yield strength, ultimate tensile strength and tensile elongation of the composite with 3.0 wt% nano-Ti addition demonstrated respectively 128.2 %, 199.6 %, 125.9 %, and 30.6 % enhancement comparing with no nano-Ti added sample. The nano Ti addition can effectively improve the wear resistance of GNPs/copper composites. The relevant structural formation, strengthening-toughening and wear mechanisms of GNPs/copper composites with nano-Ti addition were discussed.

Ultrahigh Strength and Plasticity Mechanisms of Si and SiC Nanoparticles Revealed by First-Principles Molecular Dynamics.

It is now well established that materials are stronger when their dimensions are reduced to the submicron scale. However, what happens at dimensions such as a few tens of nanometers or lower remains largely unknown, with conflicting reports on strength or plasticity mechanisms. Here, we combined first-principles molecular dynamics and classical force fields to investigate the mechanical properties of 1-2nm Si and SiC nanoparticles. These compression simulations unambiguously reveal that the strength continues to increase down to such sizes, and that in these systems the theoretical bulk strength can be reached or even exceeded in some cases. Most of the nanoparticles yield by amorphization at strains greater than 20%, with no evidence of the β-tin phase for Si. Original and unexpected mechanisms are also identified, such as the homogeneous formation of a dislocation loop embryo for the ⟨111⟩ compression of SiC nanoparticles, and an elastic softening for the ⟨001⟩ compression of Si nanoparticles.

Modeling the strength of aluminum extrusion transverse welds using the film theory of solid-state welding

Reducing production scrap is vital for decarbonizing the aluminum industry. In extrusion, the greatest source of scrap stems from removing profile sections containing transverse (charge) welds that are deemed too weak for their intended purpose. However, until now, there has been no predictive transverse weld strength model. This article establishes a transverse weld strength model as a function of billet properties and extrusion parameters. It extends the film theory of solid-state welding by enhancing Cooper and Allwood's plane strain model to consider non-plane strain deformations at the billet-billet interface. These enhancements are informed by analyzing oxide fragmentation patterns through shear lag modeling and microscopy of profiles extruded from anodized billets. Model predictions are assessed through shear tests on welds from single and two-piece billets, extruded into rod, bar, and multi-hollow profiles. The experiments reveal that negative surface expansions at the weld nose cause interface buckling and weaker welds, but both surface expansions and weld strengths increase with distance from the nose. In non-axisymmetric profiles, deformation conditions and strengths vary across, as well as along, the weld. Two-piece billet welds are longer but reach bulk strength long before weld termination. The model predicts these trends and shows that die pressures are sufficient for micro-extrusion of any exposed substrate through interface oxide cracks. This underscores the significance of interface strains in exposing substrate and determining the weld strength. The model can help increase process yields by determining minimum lengths of weak profile to scrap and aiding process optimization for increased weld strength.

First-principles molecular dynamics compression of small metallic nanoparticles

Whether the strength of materials keeps increasing, saturates or decreases when characteristic dimensions are reduced down to the nanometer scale remains an open question. To bring new insights, first principles molecular dynamics calculations are performed to model the compression of 1–2 nm aluminum nanoparticles with different shapes. We find that the plastic deformation occurs at high strains and stresses by a mechanism combining diffusive and displacive atomic displacements. This deformation mode is characterized by a slow dynamic and the partial or even complete recovery of crystalline order. The strength depends on the nanoparticles shape, and is in all cases significantly higher than the theoretical bulk strength. It is however substantially lower than values extrapolated using reported classical molecular dynamics investigations. Our results suggest that the strength saturates at low scales.

Relating bulk solid caking events to phase change events that happen during crystallization processes

Caking causes significant problems in the storage of bulk solids in process vessels. Caking results in large rathole formation, lumps in product, inability to empty bags, silos, hoppers, and poor flow in feeders. Caking problems reaches all levels of the production process from the large-scale silos to the small single use packages sold in stores.Caking is characterized as a gain of significant bulk strength during storage. It is responsible for many lost production hours and unscheduled downtimes in processes dealing with bulk solids – particularly powders. Caking is also mechanistic in its nature. In this paper we will deal with one of those causes. The goal of this work is to more clearly understand the relationship between the root cause of caking and the kinetics of the gain of strength observed when recrystallization results in powder caking. Detailed strength measurements seem to indicate that the caking of powders induces a gain in strength in accordance with two exponential growth terms. The first strength growth term is proportional to storage time to the 1st power. The second exponential growth term is proportional to storage time to 3rd power. It was found that this behavior was consistent with phase growth kinetics in accordance with the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. This equation suggests that within a confined space where crystallization is occurring the fraction of space that transforms into a crystalline material has kinetics consistent with exponential functions that are proportional to time to the 1st power, 2nd power, and 3rd power depending on the dimension of the crystals that form. Rods or fibers correspond to kinetics proportional to time to the 1st power. Plates correspond to kinetics proportional to time to the 2nd power. The formation of spheres or 3D clusters correspond to kinetics proportional to time to the 3rd power. The bulk strength tends to have a one-to-one correspondence to exponential crystal growth to time to the 1st and 3rd powers where the 1st power exponential strength growth happens on a short time frame and the 3rd power exponential growth happens on a longer time frame. This suggests that crystal rods or fibers first form in the pendular volume between particles followed by 3D structure formation in the pendules during bulk solid caking events. Understanding the magnitude and kinetics of these events can give engineers the information to prevent or minimize this issue.

A reusable and high shear strength hot melt adhesive with oxime-urethane bonds

Adhesives are widely used to bond various materials and surfaces, hot melt adhesives (HMAs) have conquered almost every industry area due to their solvent-free volatilization and ease of use. However, preparing reusable HMAs with high shear strength is still extremely challenging. Here, we show a simple way to prepare a reusable HMA, OPU (oxime-based polyurethane), with high lap shear strength based on oxime-urethane bonds. Cu(II) ions were introduced to further enhance the bulk strength to form ligand bonds. The relationship between the ligand bond content and the material properties was also investigated. Increasing ligand bond content limited the degree of crystallinity and shear strength. And the breaking stress and toughness of the coordinated material were significantly increased. The initial shear strengths of OPU for 304 stainless steel (after this referred to as “steel”) and aluminum reached 12.6 MPa and 9.3 MPa, respectively, which is the highest shear strength available for oxime-urethane-based polyurethane HMAs. After 10 repetitions, the OPU still retains its high shear performance. By analyzing the relationship between shear strength and the amount of Cu(II), it is found that the shear strength is strongly related to chain mobility and Young's modulus. This work demonstrates a useful way of synthesizing reusable HMAs with high lap shear strength.

Effective utilization of mine overburden soil in producing aggregates by pelletization and sintering

The mine overburden generated during mining operations remains largely unused. Though existing studies aimed at using mining waste in coarse aggregate manufacture, limited studies have emphasized the parametric investigation of the manufacturing process. This study focuses on the total volume utilization of the mine overburden soil into a value-added product for use in construction. The study used three types of mine overburden soil samples from a nearby lignite mine: red clay, ball clay and alluvial clay. The study included determining physical, chemical, mineralogical and geotechnical properties. The mine overburden was free of toxic minerals and suited to manufacture coarse aggregate using pelletization and sinter hardening. The parameters influencing aggregate manufacturing, viz., pelletization angle, speed, and moisture content were studied for each soil type to identify the optimal combination of these factors. As a next step, the sintering temperature was varied between 900 °C and 1300 °C to manufacture aggregate with a bulk density and strength range. The water absorption was about 10% for a strength of 4.8 MPa and a density range between 877 to 1195 kg/m3. SiO2, Al2O3, and other flux-forming compounds highly influenced aggregate properties.

Use Of Mining Tailings in The Manufacture of Ecological Bricks to Encourage the Construction of Sustainable Housing

This work aimed to manufacture ecological bricks using mining tailings, by-products of mining activity, to contribute to sustainable housing development. The Peruvian technical standards E.060 and E.070 are used as a reference framework to achieve this. The study focuses on various aspects, such as mineralogical analysis, particle size distribution, plasticization, workability, and rheology. The research methodology adopted is deductive, with an applied and quantitative approach. A retrolective data collection instrument and descriptive, explanatory, correlational, and descriptive level approaches are used. The results obtained from this research reveal significant findings. It was observed that including 20% of an alkaline binder based on calcined clay improves the development of bricks in areas with severe climatic conditions. In addition, incorporating lime fibers reduces thermal conductivity and increases bricks' compressive and bending strength. Blocks containing 30% clay cork reinforce the bricks' bulk density, thermal conductivity, and strength. On the other hand, it was verified that tailings with lead-zinc sulfide, reduced by 47%, comply with the carbonization and contraction coefficient. Shale, fly ash, and cement tailings achieved a compressive strength of 26 MPa and a water absorption rate of 14.32%. The addition of steel filings by 3% improves compressive strength. Likewise, incorporating plastic waste increases the compressive strength to reach 37.5 MPa. As for geopolymers, it was observed that viscosity recovery is in a range between 65% and 82%. Finally, recycled aggregates, with a maximum nominal size of 3/8" and 1/4", meet the standard requirements, providing a compressive strength of up to 8 MPa. Finally, this study demonstrates the potential of using mining tailings and other recycled materials to manufacture ecological bricks for sustainable housing development in mining communities, offering viable solutions from an environmental and construction point of view.

Evaluation of equi‐biaxial strength of thin sic coatings using ring‐on‐ring testing and digital image correlation

AbstractTo assess the strength of coatings under multi‐axial stress conditions, a method was developed to evaluate the biaxial strength of thin silicon carbide (SiC) coatings using a ring‐on‐ring test. A graphite substrate was used as an intermediary to transmit stress from the load ring to the coated specimen, and the thin coating was subjected to a uniform equi‐biaxial stress. The strain in the thin film was continuously monitored using digital image correlation, allowing the identification of the time at which and when the initial crack occurred; the stress applied to the loading area at time was determined to be the fracture strength of the thin SiC films. The obtained fracture strength ranged from 209 to 1014 MPa and was dependent on specimen volume. Notably, the thinnest specimen exhibited the highest strength, whereas the strengths of thicker specimens approached previously reported bulk strengths.

Nacre-inspired boron nitride/sodium alginate composite with enhanced mechanical properties by prestress

Prestressing strategies are widely adopted in the formation of biological structures to modify their mechanical property. Inspired from the prestress generation during the formation of biominerals, a nacre-inspired boron nitride (BN) nanosheets strengthened by prestressed sodium alginate (SA) matrix is fabricated. The BN/SA (BS) films are formed by freeze-casting and pressing, then immerse in ethanol (BS-E) or CaCl2 solution (BS-Ca). Several megapascals contractile stress is generated in film that is attributed to the contraction and crosslink of SA chains. Subsequently, artificial bulk composites are fabricated by stacking of these prestressed films via hot-pressing. Benefit from the contractile stress, the orientations of BN nanosheets in BS-E and BS-Ca are improved, and the (002) interplanar spacing of BN nanosheets in BS-Ca bulk is slight expansion compared with BS. Finally, the flexural strength of BS-E bulk is enhanced from 145 MPa (BS) to 174 MPa when the loading direction is parallel to stacking.

A proposed method for optimizing coal pillar design using coalfield-specific uniaxial compressive strength

The research described considers whether the variability in coal material strength, as derived through a series of uniaxial compressive strength (UCS) tests, could be used to indicate the variability in coal pillar strength. The aim is to be able to use a distribution of UCS tests as input into the coal pillar strength calculation. This will allow the pillar design to be expressed in terms of a probability of failure rather than as the commonly used safety factor. To achieve this, the bulk strength factor associated with commonly used pillar strength formulae was replaced with a distribution of UCS results divided by an adjustment factor. The factor was determined so as to ensure that the resulting bulk strength does not deviate from the statistically determined bulk strength published in the original formulae. This approach enabled pillar strength distributions to be obtained using industry-accepted strength formulae, subsequently allowing for a probability of failure to be calculated for a specific pillar design. Using a regional coal material strength curve as a baseline, coalfields in which the coal is stronger than the regional mean can be identified and the pillar designs optimized. This is based on the stronger coals achieving lower probabilities of failure at similar safety factors. The research has considered actual UCS data from multiple mines in the Mpumalanga coalfields of South Africa, and has proved that the variability in material strength between coalfields could allow for some optimization using the proposed approach. Based on the data used in the study, a 2.78% increase in extraction could be achieved. However, further research will be required to validate the results of the study in an underground environment.