Inferior Mechanical Properties Research Articles

Bioresorbable magnesium-reinforced PLA membrane for guided bone/tissue regeneration

Considering the inferior mechanical properties of the current bioresorbable polymers, a novel bioresorbable magnesium-reinforced polylactide (PLA) membrane was designed for the application in critical defect sites in guided bone/tissue regeneration. The PLA-FAZ91 membrane was fabricated by combining two PLA membranes with a fluoride-coated AZ91 (9 wt% Al, 1 wt% Zn) (FAZ91) magnesium alloy core by hot pressing. A combined double-layered PLA membrane was used as the control group. A three-point bending test was performed to compare their maximum load and stiffness. Samples were immersed in the HBSS for 20 weeks, and their weight loss percentages were recorded, and a three-point bending test was performed after immersion. An ion release test was performed by immersing samples in the HBSS for 4 weeks and determining the pH and ion concentrations of the HBSS. Cell viability was tested by culturing pre-osteoblast cells with sample extracts in the culture medium obtained from degraded samples. As a result, PLA-FAZ91 showed a significantly higher maximum load and stiffness than those of the non-reinforced PLA membrane. The weight loss of PLA-FAZ91 was much faster, as FAZ91 showed major degradation and was completely degraded after 16–20 weeks of immersion. The degradation of the PLA wrap was accelerated by FAZ91. The mechanical superiority of PLA-FAZ91 over PLA endured for at least 3 weeks during immersion. The pH, magnesium- and fluoride-ion concentration in the PLA-FAZ91 group increased at an appropriate rate. The cell viability was not adversely affected by the addition of FAZ91 to PLA. Therefore, the bioresorbable magnesium-reinforced PLA membrane has the potential to be used as a good alternative to pure PLA membrane in guided bone/tissue regeneration.

Alloying criteria and investigations on the properties of novel AM series alloy fabricated using stir casting

Abstract Magnesium alloys are being used in different sectors for several applications. The low density and high strength to weight ratio have made them indispensable. However, it is observed that Mg alloys are less preferred for the fabrication of critical and complex parts. The inferior mechanical and corrosive properties, along with high inflammability, limit their usage for several applications. The mechanical and physical properties can be enhanced by varying the weight percentage of alloying elements along with an appropriate process for its development. The paper discusses an approach for selection of the alloying elements and their weight percentage with the help of phase diagrams, vital inputs from past literature and properties of commercially available Mg alloys. The developed AM series alloy (Mg-7 wt%Al-0.9 wt%Mn) has shown improvement in the mechanical properties vis-a-vis the existing AM series alloys. The elastic modulus and hardness were observed 24.3% and 16.21% higher than the maximum values of existing AM alloys. For the development of alloy, a systemized stir casting setup was used, which ensured uniform mixing of alloying elements and essentially played an active role in enhancing the mechanical properties.

Physical and mechanical properties of wood and their geographic variations in Larix sibirica trees naturally grown in Mongolia

We examined the physical and mechanical properties of wood in Siberian larch (Larix sibirica) trees that grow naturally in five Mongolian provenances (Khentii, Arkhangai, Zavkhan, Khuvsgul, and Selenge) and the geographic variations between them. Five trees with stem diameters of 20 to 30 cm at 1.3 m above ground were collected from each provenance. The mean values of the modulus of elasticity (MOE), modulus of rupture (MOR), compressive strength parallel to grain (CS), and shearing strength (SS) ranged from 7.03 to 9.51 GPa, 79.8 to 103.9 MPa, 46.3 to 51.1 MPa, and 10.4 to 13.0 MPa, respectively. Significant differences were found in radial and tangential shrinkage, MOE, MOR, and SS in wood among the five provenances. In addition, juvenile wood had inferior physical and mechanical properties in comparison to mature wood within and among provenances. Furthermore, there were significant differences in all examined properties, except for CS, in mature wood among the five provenances. Higher correlation coefficients were also obtained in mature wood among all mechanical properties, except for SS.

Stress-Actuated Spiral Microelectrode for High-Performance Lithium-Ion Microbatteries.

Miniaturization of batteries lags behind the success of modern electronic devices. Neither the device volume nor the energy density of microbatteries meets the requirement of microscale electronic devices. The main limitation for pushing the energy density of microbatteries arises from the low mass loading of active materials. However, merely pushing the mass loading through increased electrode thickness is accompanied by the long charge transfer pathway and inferior mechanical properties for long-term operation. Here, a new spiral microelectrode upon stress-actuation accomplishes high mass loading but short charge transfer pathways. At a small footprint area of around 1 mm2 , a 21-fold increase of the mass loading is achieved while featuring fast charge transfer at the nanoscale. The spiral microelectrode delivers a maximum area capacity of 1053 µAh cm-2 with a retention of 67% over 50 cycles. Moreover, the energy density of the cylinder microbattery using the spiral microelectrode as the anode reaches 12.6 mWh cm-3 at an ultrasmall volume of 3 mm3 . In terms of the device volume and energy density, the cylinder microbattery outperforms most of the current microbattery technologies, and hence provides a new strategy to develop high-performance microbatteries that can be integrated with miniaturized electronic devices.

Properties of Biomimetic Artificial Spider Silk Fibers Tuned by PostSpin Bath Incubation.

Efficient production of artificial spider silk fibers with properties that match its natural counterpart has still not been achieved. Recently, a biomimetic process for spinning recombinant spider silk proteins (spidroins) was presented, in which important molecular mechanisms involved in native spider silk spinning were recapitulated. However, drawbacks of these fibers included inferior mechanical properties and problems with low resistance to aqueous environments. In this work, we show that ≥5 h incubation of the fibers, in a collection bath of 500 mM NaAc and 200 mM NaCl, at pH 5 results in fibers that do not dissolve in water or phosphate buffered saline, which implies that the fibers can be used for applications that involve wet/humid conditions. Furthermore, incubation in the collection bath improved the strain at break and was associated with increased β-sheet content, but did not affect the fiber morphology. In summary, we present a simple way to improve artificial spider silk fiber strain at break and resistance to aqueous solvents.

Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates (15 × 300 × 180 mm3) of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries. Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy, which is sensitive to the welding heat input. In the experiment, the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current. Tensile, micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints. Radiographic inspection was performed to assess the joint’s quality and welding defects. The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy. It was established that porosity was progressively abridged by the increase of heat input. The results also clinched that the use of medium heat input (1–2 kJ/mm) offered the best mechanical properties by eradicating welding defects, in which only about 18.26% of strength was lost. The yield strength of all the welded specimens remained unaffected indicated no influence of heat input. Partially melted zone (PMZ) width also affected by heat input, which became widened with the increase of heat input. The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone. Charpy impact testing revealed that the absorbed energy by low heat input specimen (welded at high speed) was greater than that of high heat input (welded at low speed) because of low porosity and the formation of equiaxed grains which induce better impact toughness. Cryogenic (−196 °C) impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input. Finally, Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy (SEM), which have supported the experimental findings.

A high coordination of cross-links in fiber bundles prevents local strain concentrations

We investigate the influence of the coordination of cross-links on the plastic (i.e., permanent) deformation in cross-linked fiber bundles. Yield strain and strength as well as the resilience are studied as a function of cross-linker and grafting density. It is found that classical twofold coordinated cross-links lead to a pronounced strain concentration in the system, while cross-links with higher coordination allow for a more homogeneous load transfer through the system. This results in inferior mechanical properties related to plastic behavior in the first system compared to the latter. Particularly, in twofold coordinated systems, the resilience shows a non-monotonic behavior with respect to cross-linker density. This means that inserting always more and stronger cross-links do not necessarily improve the mechanical performance of a material. These findings may help to interpret experimental findings on the fracture energy in hydro-gels cross-linked with zinc ions.

Promotion of molecular diffusion and/or crystallization in fused deposition modeled poly(lactide) welds

Fused deposition modeled parts of polymeric origin exhibit inferior interlayer mechanical properties. To enhance interfacial weld stiffness, poly(lactide) blends containing low molecular weight polymers of chemically identical but enantiomerically different nature are explored. The enantiomeric composition of the low molecular weight fraction is either random or opposite, promoting molecular diffusion or nucleation respectively. The structure-relationship of the interfaces is studied using torsional stiffness, calorimetry, and rheology. Fully miscible, non-crystallizable low molecular weight additives of random L and D enantiomeric composition reduce melt viscosity and crystallization rate, promoting molecular diffusion. Nevertheless, incomplete entangling and crystallization upon interfacial mixing induce poor interfacial stiffening. Poly(lactide) stereocomplex enriched interfaces promote crystallization. Chains across weld interfaces may be mechanically anchored in crystals, but hindered diffusion limits molecular mixing and thus the extent of mechanical stiffening. Ultimately, combining melt plasticization and increased crystallization rates distinctly increases weld stiffness and thermodynamic/geometrical stability of fused deposition modeled poly(lactides).

Graphite fabric reinforced PAEK composites by novel impregnation-co-film technique

High performance polymers such as Poly(ether ether ketone) (PEEK), Poly(aryl ether ketone) (PAEK), Poly(ether ketone ketone) (PEKK), etc exhibit high melting points, 343 °C, 373 °C and 338 °C respectively and very high melt viscosity. They do not have appropriate solvents, which could open the ways to process their fabric reinforced composites; by impregnation technique followed by compression molding. Film stacking and powder sprinkling are the only possible techniques, which lead to weak crossover points due to non-wetting by the resin and finally resulting in inferior mechanical and interfacial properties and high amount of voids. In order to solve these problems, a novel technique called impregnation-co-film (ICF) is explored in this work. Polyetherimide (PEI) (10 wt% in dichloromethane solution) pre-impregnated graphite fabric prepregs were used before applying film technique followed by compression molding. The study compares properties such as density, void content, flexural strength, impact strength, Interlaminar shear strength (ILSS), thermal stability (in air) and interface by field emission scanning electron microscopy for the composite prepared with film stacking technique and that by impregnation-co-film stacking technique. It was confirmed that the new ICF technique proved to be significantly promising than the older technique almost in all aspects with 120% improvement in ILSS, 127% in flexural strength and 200% decrease in void content.

Effect of inclusions on microstructure and mechanical behavior of multi-pass welded naval grade steel

This paper assesses the metallurgical characteristics and mechanical properties of multi-pass gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of micro-alloyed steel DMR 249-A. The prime objective was to carry out a comparative study of the microstructure and mechanical properties of the joints produced by the two types of welding. A high volume of larger sized inclusions in GMAW contributed to inferior mechanical properties. The coarse-grained part of the heat-affected zone (CGHAZ) showed a lower microhardness. Fracture always occurred in the heat-affected zone, and it is believed that it is associated with CGHAZ. GTAW joints showed low tensile residual stress, higher hardness, and tensile strength. GTA weldment also showed superior impact toughness at sub-zero temperature (–60 °C). Mn-containing inclusions were seen in GTA weldments; it is believed that they promote the formation of acicular ferrite. This is believed to be responsible for the superior mechanical properties of GTA weldments. The microstructural analysis of the two weldments revealed the presence of a higher volume fraction of acicular ferrite in the GTAW. All in all, GTAW joint was found to perform better than GMAW joint.

A Novel Approach of Bulk Strength Enhancement through Microbially-Mediated Carbonate Cementation for Mylonitic Coal

Mylonite coal is known to be highly tectonically deformed coal and is a result of crushing original coal into fine-grained coal under multiple tectonic events. Because of its granular nature and the resultant inferior mechanical property, the borehole stability during both drilling and gas drainage is challenging due to unpredictable failures. This study explored a potential approach to enhance the bulk strength of mylonitic coal via microbiologically-mediated CaCO3 cementation which effectively increases the cohesion of the fine coal particles through the bio-cementation process. The experimental results indicated that the mechanical strength was significantly enhanced after a short period of biotreatment with 12 cycles of biotreatment yielding a maximum stiffness of 32 KN/mm and maximum uniaxial compressive strength of 9.3 MPa. The strength evolution behavior demonstrated that the macroscopic failure behavior of mylonite coal evolves from plastic failure to brittle failure as the increase of bio-treatments. The results from XRD indicated that the generated CaCO3 crystals mainly occurs in the form of calcite and vaterite. Imaging by SEM further indicated the cementation process for CaCO3. The generated CaCO3 precipitation first occurs on random spots on the particle surfaces, and then occupies the interstitial space until particle-particle bonds are generated.

Lifetime estimation of Cr2AlC MAX phase foam based on long-term oxidation and fracture mechanisms

Oxidation kinetics and mechanical behaviours of Cr2AlC foam with a porosity of 53 vol.% were investigated. Microstructures of Cr2AlC foams oxidised in the temperature range 1173 to 1473 K for times between 0 and 100 h were examined. Uniaxial compression tests were performed at different temperatures in the range 298–1398 K to assess mechanical properties. The oxidation formed cohesive Al2O3 layers on the Cr2AlC matrix, beneath which porous Cr7C3 was formed. The oxidation kinetics can be expressed by a parabolic law. An excessive oxidation took place first in thin struts, where a breakage Al2O3 layer occurred, followed by an oxygen inflow and decomposition of inner material. At 298 K, non-oxidised Cr2AlC foam fracured intergranularly. Slight oxidation improved compressive strength, as the Al2O3 layer (2.5 µm or thinner) can prevent cracks to propagate from inside outward. However, an excessive oxidation deteriorated any improvement due to the breakage of Al2O3 layer in thin struts followed by the material decomposition. At 1273 K and 1398 K, non-oxidised porous Cr2AlC fractured intergranularly, accompanied by a plastic deformation around small Al2O3 particles segregated at grain boundaries. Oxidised Cr2AlC foams with the Al2O3 thickness of 2.5 µm had a slightly higher brittle-to-plastic transition temperature (~1273 K) than dense Cr2AlC. A thicker Al2O3 layer (~5 µm) was required to reinforce the material due to inferior mechanical properties of Cr2AlC at high temperatures. On the basis of the elucidated oxidation and fracture mechanisms, a safety criterion for high-temperature applications was suggested.

Improving flame resistance and mechanical properties of magnesium–silver–calcium sheet alloys by optimization of calcium content

Abstract Low flame resistance and inferior mechanical properties are critical issues in widening applications of wrought magnesium alloys as a structural component. To address these issues, the present authors attempted to develop a flame-resistant magnesium–silver-based sheet alloy with excellent room temperature (RT) formability. It was found that the ignition temperature of Mg–1.5 wt%Ag–x wt.%Ca alloy was significantly increased with increasing the Ca content up to 2 wt%. The 2 wt% Ca-containing alloy exhibited a non-flammability characteristic upon 1000 °C due to the formation of compact and dense CaO film on the surface. Strength and in-plane yield anisotropy were enhanced with increasing the Ca content, which were mainly associated with a finer microstructure and a denser distribution of Mg2Ca second phase particles. In contrast, stretch formability was decreased with increasing the Ca content due to an increased number of the Mg2Ca particles. A compositionally optimized Mg–1.5Ag–1Ca (wt.%) alloy showed a high ignition temperature of 912.5 °C with a large index Erichsen value of 7.8 mm at RT.

Investigating the mechanical, thermal and melt flow index properties of HNTs – LLDPE nano composites for the applications of rotational moulding

Linear low density polyethylene (LLDPE) is the one of the most popular polymer used for rotational moulding applications such as storage tanks. But, its inferior mechanical properties and thermal stability restrict the longer service. Hence, this study experimentally demonstrates the effect of Halloysite Nanotube (HNTs) concentration on LLDPE composites for enhancing the mechanical and thermal stability. HNTs were uniformly dispersed with LLDPE matrix through ultra-sonication, followed by compression moulding used to prepare the nano composites plates. The prepared composites are shown 19.2% improved tensile strength for 2 wt% HNTs, whereas 28.9% hike in flexural strength observed for 4 wt% HNTs composite, compare to neat LLDPE. Which shows that higher concentrations of HNTs is favourable in improving the flexural strength rather than tensile properties. In addition to that, higher concentrations of HNTs are also helping in improving the storage modulus of the LLDPE composites. The increase in mechanical properties mainly attributed due to effective load carriers (HNTs) in the composite. Besides, HNTs were also contributing for improving the melting point and residual char of the composites, which is indeed for storage tanks durability. The prepared composite was thermally stable at higher temperature up to 230 °C, because of HNTs chemical structure, the inner layer of HNTs constitute with Al2O3 and outermost layer constitute with SiO2, both are thermally stable. Stated enhancement proves the potential effect of HNTs reinforcement in the LLDPE composite for rotational moulding applications.

Achilles tendon elongation after acute rupture: is it a problem? A systematic review.

Rupture of the Achilles tendon (AT) is a common injury. Strength deficits may persist over the long term, possibly owing to elongation of the tendon or inferior mechanical properties. This study aimed to provide a systematic review of the literature on the prevalence and consequences of tendon elongation in patients after acute AT rupture treatment. It was hypothesized that an elongated tendon would be associated with a worse clinical outcome. The databases for MEDLINE, CENTRAL and Web of Science were searched. Clinical studies related to AT rupture reporting tendon elongation and clinical or functional outcomes, with a minimum follow-up of 6months, were eligible for inclusion. Only studies testing for statistical correlations (SCs) between AT elongation and other outcomes were eligible, with the exception of biomechanical studies in which statistically significant AT elongation was found to be a generalized finding in the study group. For these studies to be eligible, the study group had to be compared with a healthy control group, or the injured limb compared with the uninjured limb, regarding biomechanical parameters. Twenty-eight papers were selected for inclusion. Mean AT elongation measured with imaging techniques ranged from 0.15 to 3.1cm (n = 17). Ten studies investigated SCs with Patient Reported Outcome Measures (PROMs), in which two found SCs with tendon elongation. Five studies reported strength and power evaluations and their correlation with AT elongation, with two having found SCs between decreased strength and tendon elongation. In ten studies reporting data on biomechanical tests, nine found influence of tendon elongation. In this group, four out of five studies found SCs with biomechanical parameters. Fair evidence of the influence of tendon elongation in biomechanical parameters was found. In a general population, evidence of a detrimental effect of tendon elongation on PROMs or functional strength at follow-up was not found in this review. Level IV.

A review on the reactivation of hardened cement paste and treatment of recycled aggregates

The generation of construction and demolition waste (CDW) worldwide keeps on escalating due to growth in infrastructure and the related refurbishment or replacement of existing structures. Numerous research studies on the utilisation of CDW materials in the production of new concrete have been conducted, from which it has been established that their use generally leads to inferior mechanical properties of the resulting concrete. As such, the general acceptance and conventional utilisation of CDW in the construction industry is undermined. The concept of a triple-layered interfacial transition zone is suggested to be the main reason for the inferior mechanical properties exhibited by recycled aggregate (RA) concrete. Past research on the reactivation of hydrated cement paste and on improving the quality of RAs by the use of different treatments, was reviewed. The review revealed that a combination of mechanical grinding and thermal treatment at temperatures of 500–800°C is an effective means of activating the cementitious properties of hardened cement paste. Adhered mortar removal and mortar fortification are the main approaches for enhancing the properties of RAs. Mechanical abrasion and/or thermal treatment at a temperature of 500°C, are the most effective techniques for improving the properties of RAs.

HORMIGÓN DE BAJAS PROPIEDADES RESISTENTES REFORZADO CON FIBRAS DE POLIOLEFINA: CONSIDERACIONES Y DISEÑO DE UN HORMIGÓN ESTRUCTURAL COMPETITIVO

Polyolefin fibre reinforced concrete (PFRC) has become an attractive alternative to steel fibre reinforced concrete for structural applications. Although PFRC has shown capacity for meeting the structural requirements set in the regulations sometimes, complying with the residual strength value at 0,5mm of crack opening (fR1) might be a challenge. That value is aimed at avoiding brittleness of the concrete element and in certain occasions require fibre dosages close to 6kg/m³. Most of the previous studies have been performed with normal or high quality concretes and consequently their strength at the end of the limit of proportionality (fLOP) is also remarkable. Given that the residual strength at fR1 is proportional to fLOP, manufacturing of a concrete with inferior mechanical properties would allow production of one that encountered fewer issues related with brittleness and offered improvement in tensile and flexural strength at a reduced cost. In this study, several concretes with reduced mechanical properties and with 6 and 7,5kg/m³ of polyolefin fibres were manufactured. Their mechanical response was analysed in order to determine if they were apt for their use in low responsibility structural concrete members. Moreover, the influence of the method used to add the fibres was studied by adding the fibres in two different ways adding them individually from sacks or using pucks (50g each one). Keywords: Polyolefin fibre reinforced concrete, regulation requirements, moderate strength concrete.

Effects of vacancy defects on the mechanical properties of graphene/hexagonal BN superlattice nanoribbons

Two kinds of vacancy defects, rhombic and square nanoholes, were produced in graphene/hexagonal BN (g/h-BN) superlattice nanoribbons by ion irradiation. The effects of the type (rhombus and square), area, number density and position of the nanoholes, and the period length of the nanoribbons on their mechanical properties were investigated by molecular dynamics simulation. The results show that the failure strength and strain of the nanoribbons are more sensitive to vacancy defects than is the Young's modulus. The mechanical properties are insensitive to the period length of the nanoribbons and those with rhombus nanoholes have inferior mechanical properties to those with square nanoholes under the same conditions. The mechanical properties of the nanoribbons are largely affected by the positions of the nanoholes, such that they should be in the graphene and not in boron nitride as much as possible. By increasing the number density of the nanoholes, the toughness of the nanoribbons is increased.

Investigation of torsional fatigue failure of a centrifugal pump shaft

Shafts of centrifugal pumps are both load bearing and power transmitting component which are usually composed of martensitic stainless steel. In this paper, an attempt is made to manifest how minute deviations from the standard dimensions of the keyway of a shaft leads to the occurrence of premature torsional fatigue along the keyway seat. Microstructural characterization via optical microscope, SEM and EDS further revealed faulty heat treatment of the material that resulted in inferior mechanical properties which assisted in the accelerated crack propagation and ultimate failure of the shaft within 2.5 years of service leading to a shutdown of blast furnace for approximately 10 h. Comparative material analysis was carried out on samples of shaft from other pumps in service (which has not failed) to manifest that proper heat treatment of the shaft material can bring about desired mechanical properties of component and procrastinate the failure.

Influence of silane‐modified coconut shell powder on thermal and mechanical properties of thermoplastic elastomers

AbstractA silane coupling agent (glycidyloxypropyltrimethoxysilane, GPTMS) was used to modify coconut shell powder (CSP), and the influence of the modified coconut shell powder (G‐CSP) on the thermal and mechanical properties of thermoplastic elastomers (TPEs) was investigated. The thermal stabilities of the G‐CSP‐TPEs were studied using TGA; Young's modulus of the G‐CSP‐TPEs was studied by means of the spherical indentation test and the tensile test, and the tensile test was also used to characterize the tensile strength of the G‐CSP‐TPEs. The results revealed that the specific functional groups of GPTMS were efficiently grafted onto the CSP and that G‐CSP enhanced the thermal stability of the TPEs. Under 8% strain, Young's moduli of 0–7.5 wt% G‐CSP‐TPEs obtained by the spherical indentation test and tensile test were almost equal, while the modulus of 10–15 wt% G‐CSP‐TPEs measured by the latter test was greater than that of the former test. The tensile strength of G‐CSP‐TPEs increased up to a threshold limit (10 wt% G‐CSP), followed by a significant decrease. Micro‐images of the fractured surfaces obtained by SEM indicated that the addition of G‐CSP gradually filled the microvoids in the matrix and enhanced the tensile strength of the composite. As the G‐CSP mass percentage exceeded a threshold limit (>10 wt%), the particles started to agglomerate, resulting in weak interfacial adhesion and inferior mechanical properties. Hence, an optimal amount of reinforcing agent G‐CSP should be added to attain desirable thermal and mechanical properties. © 2020 Society of Chemical Industry