Great Toughness Research Articles

Great toughness reinforcement of isotactic polypropylene/elastomer blends with quasi-cocontinuous phase morphology by traces of β-nucleating agents and carbon nanotubes

Aiming at obtaining the polyolefin blends potentially applied in the field of the super-tough polymer products, in this work, isotactic polypropylene (iPP)/styrene-ethylene-butadiene-styrene block copolymer (SEBS) blends with great impact toughness were successfully fabricated by adding traces of β-nucleating agents (β-NAs) and carbon nanotubes (CNTs). The impact toughness of iPP blends with 30 wt% SEBS was as high as 62.4 kJ/m2, when simultaneously containing 0.1 wt% β-NAs and 0.05 wt% CNTs. Their toughness was about 13.1 kJ/m2 more than iPP blends with 30 wt% SEBS and 0.1 wt% β-NAs, 49.6 kJ/m2 more than iPP blends with 30 wt% SEBS and 0.05 wt% CNTs, and almost 22.3 times of pure iPP. The iPP matrix with abundant self-toughed β-crystals generated by β-NAs, the quasi-cocontiunous morphology of the SEBS dispersed phase as well as some small SEBS droplets induced by CNTs in the iPP matrix, and the good interfacial compatibility between SEBS and the iPP matrix all harmoniously took effect to synergistically enhance the toughness of iPP blends.

A general bio-inspired, novel interface engineering strategy toward strong yet tough protein based composites

Biopolymers show a broad prospect as an effective alternative to petroleum-based materials. However, assembling biopolymers into the composites with integrated high strength and toughness still remains a great challenge. Herein, we developed a novel and versatile mussel-inspired modification design for tough and high-performance graphene oxide (GO)/soy protein isolate (SPI) nanocomposite films, where the GO nanosheets were modified with poly(dopamine) (PDA) to improve the dispersion of GO nanosheets in SPI matrix and enhance their interfacial adhesion. As expected, at 0.6 wt% of PDA-modified GO (PDG) loading, the tensile strength and toughness of the SPI/PDG films reached 8.87 MPa and 22.82 MJ m−3, respectively, which simultaneously showed 86.34% and 263.95% higher than those of pristine film. The great enhancement of mechanical behaviors was due to the increased fracture line energy and the lack of significant coalescence of microcracks, as well as the strong interfacial adhesion force between peptide chains and PDG nanosheets. The resultant nanocomposite films also exhibited favorable vapor barrier behavior and water-resistance. The proposed method in this paper opens a new avenue for assembling two-dimensional nanosheets into the biopolymer-based composites with integrated high strength and great toughness for a series of innovative future applications.

A 3D Printable and Mechanically Robust Hydrogel Based on Alginate and Graphene Oxide

Sodium alginate (SA) was used for the first time to noncovalently functionalize amino-graphene oxide (aGO) to produce the SA-functionalized GO, A-aGO. A-aGO was then filled into a double-network (DN) hydrogel consisting of an alginate network (SA) and a polyacrylamide (PAAm) network. Before UV curing, A-aGO was able to provide the SA/PAAm DN hydrogel with a remarkable thixotropic property, which is desirable for 3D printing. Thus, the A-aGO-filled DN hydrogel could be nicely used as an "ink" of a 3D printer to print complicated 3D structures with a high stackability and high shape fidelity. After UV curing, the 3D-printed A-aGO filled DN hydrogel showed robust mechanical strength and great toughness. For the function of A-aGO it was considered that A-aGO acted as a secondary but physical cross-linker, not only to give the hydrogel a satisfactory thixotropic property but also to increase the energy dissipation by combining the physical SA network and the chemical PAAm network. As an exciting result we successfully developed a 3D printable and mechanically robust hydrogel.

Granular Nanostructure: A Facile Biomimetic Strategy for the Design of Supertough Polymeric Materials with High Ductility and Strength.

The realization of high strength, large ductility, and great toughness for polymeric materials is a vital factor for practical applications in industry. Unfortunately, until now this remains a huge challenge due to the common opposing trends that exist when promoting improvements in these properties using materials design strategies. In the natural world, the cuticle of mussel byssus exhibits a breaking strain as high as 100%, which is revealed to arise from an architectural granular microphase-separated structure within the protein matrix. Herein, a facile biomimetic designed granular nanostructured polymer film is reported. Such biomimetic nanostructured polymer films show a world-record toughness of 122 (± 6.1) J g-1 as compared with other polyvinyl alcohol films, with a breaking strain as high as 205% and a high tensile strength of 91.2 MPa, which is much superior to those of most engineering plastics. This portfolio of outstanding properties can be attributed to the unique nanoscale granular phase-separated structure of this material. These biomimetic designed polymer films are expected to find promising applications in tissue engineering and biomaterials fields, such as artificial skin and tendon, which opens up an innovative methodology for the design of robust polymer materials for a range of innovative future applications.

Effect of acetylation on the chemical composition of hornbeam (Carpinus betulus L.) in relation with the physical and mechanical properties

ABSTRACTCommon hornbeam (Carpinus betulus L.) is a highly underused wood species despite its great hardness, strength, wear-resistance and toughness. It is mainly used as firewood in Hungary because of its wood defects, irregular shape and low-dimensional stability. These wood defects and small breast height diameter result in a low yield. It is non-durable outdoors as it tends to turn grey, crack and be attacked by wood-decaying organisms. Indoors it lasts for hundreds of years. One technology that could improve the stability and durability properties is acetylation. Hornbeam was acetylated with the Accoya® method under industrial conditions. The aim of this research was the assessment of acetylation affecting the chemical properties of hornbeam wood and how these are related to the change in physical and mechanical properties. Main wood constituents (cellulose, hemicellulose, Klason lignin, extractives and ash content) were determined and compared. Chemical parameters related to the degradation of structural polymers were also evaluated (total phenolic and soluble carbohydrate contents, pH and buffering capacity, furfural, levulinic acid, formic acid, acetic acid). Structural changes in acetylated wood and in the Klason lignin fraction were also assessed using FTIR spectroscopy.

Effect of Conditions of Cryogenic Treatment on the Properties of Selected Cold Work Tool Steels*

Abstract The paper evaluates the properties of two cold work tool steels which differ in the production process and content of carbon and vanadium. Both steels are characterized by their great hardenability, toughness, dimensional stability and wear resistance. They are a subledeburitic steel X63CrMoV5-1 produced by classical metallurgy and a ledeburitic steel Vanadis 6 produced by powder metallurgy. Different austenitizing temperatures in the range of recommended values for the material were used during the heat treatment. Both materials were tempered at a temperature of 530 °C. Also cryogenic treatment at temperatures of −196 °C and −180 ° C for 5 h and/or 4 h was inserted into the conventional heat treatment cycle. The effect of the timing of cryogenic treatment in the heat treatment cycle was observed. Hardness measurement, a three-point bending test and a wear resistance test by the pin-on-disk method were used to specify the effect of the conditions of heat treatment on the properties of the investigated materials.

Toughness enhancement of tungsten reinforced with short tungsten fibres

The feasibility and toughening efficiency of the short tungsten fibre reinforcement on tungsten were investigated in Wf/W composites fabricated by powder metallurgy method of spark plasma sintering. Fibres in the composites presented a Z-free laminar structure. Partial recrystallization of fibre grains occurred but fibre crack or damage was not detected. Fracture energy of Wf/W composites was estimated in tensile tests, and the results indicated great toughness improvement over pure tungsten in virtue of frictional pullout and plastic deformation of fibres, and matrix-fibres interfacial debonding since 873K. The specimen with mass fraction of 10% and fibre diameter of 100µm exhibits the largest elongation of 9±1.1% and the highest ultimate strength of 482±13MPa at 873K.

A General Bioinspired, Metals-Based Synergic Cross-Linking Strategy toward Mechanically Enhanced Materials.

Creating lightweight engineering materials combining high strength and great toughness remains a significant challenge. Despite possessing-enhanced strength and stiffness, bioinspired/polymeric materials usually suffer from clearly reduced extensibility and toughness when compared to corresponding bulk polymer materials. Herein, inspired by tiny amounts of various inorganic impurities for mechanical improvement in natural materials, we present a versatile and effective metal ion (Mn+)-based synergic cross-linking (MSC) strategy incorporating eight types of metal ions into material bulks that can drastically enhance the tensile strength (∼24.1-70.8%), toughness (∼18.6-110.1%), modulus (∼21.6-66.7%), and hardness (∼6.4-176.5%) of multiple types of pristine materials (from hydrophilic to hydrophobic and from unary to binary). More importantly, we also explore the primarily elastic-plastic deformation mechanism and brittle fracture behavior (indentation strain of >5%) of the synergic cross-linked graphene oxide (Syn-GO) paper by means of in situ nanoindentation SEM. The MSC strategy for mechanically enhanced integration can be readily attributed to the formation of the complicated metals-based cross-linking/complex networks in the interfaces and intermolecules between functional groups of materials and various metal ions that give rise to efficient energy dissipation. This work suggests a promising MSC strategy for designing advanced materials with outstanding mechanical properties by adding low amounts (<1.0 wt %) of synergic metal ions serving as synergic ion-bonding cross-linkers.

Wear resistance performance of boron nitride coatings on end milling cutters

For defence industry applications, the machining of ultra-high strength steels or aluminium with ballistic temper grades is a widely-used operation. Therefore, it is a great challenge to find an optimum solution for tool wear. In that sense, tool coatings provide various solutions for machining of hard materials or improving wear resistance. A cost-effective tool coating provides longer tool life, hence decreases the tool cost contribution in production. Boron nitride (BN) coating could be thought as a new generation coating method compared to titanium nitride (TiN), aluminium titanium nitride (AlTiN) or silicon aluminium oxy-nitride (SiAlON). BN coating material has a great strength, toughness and chemical stability whereas it has an important disadvantage of high intrinsic stress. In this industrial study, standard end mill cutters are coated with BN material by physical vapour deposition (PVD) method. The coated and uncoated milling tools are compared according to their wear resistance and the obtained workpiece surface roughness. First results of the study are presented in this paper.

Wear resistance performance of boron nitride coatings on end milling cutters

For defence industry applications, the machining of ultra-high strength steels or aluminium with ballistic temper grades is a widely-used operation. Therefore, it is a great challenge to find an optimum solution for tool wear. In that sense, tool coatings provide various solutions for machining of hard materials or improving wear resistance. A cost-effective tool coating provides longer tool life, hence decreases the tool cost contribution in production. Boron nitride (BN) coating could be thought as a new generation coating method compared to titanium nitride (TiN), aluminium titanium nitride (AlTiN) or silicon aluminium oxy-nitride (SiAlON). BN coating material has a great strength, toughness and chemical stability whereas it has an important disadvantage of high intrinsic stress. In this industrial study, standard end mill cutters are coated with BN material by physical vapour deposition (PVD) method. The coated and uncoated milling tools are compared according to their wear resistance and the obtained workpiece surface roughness. First results of the study are presented in this paper.

Effect of hydroxyapatite concentration on high-modulus composite for biodegradable bone-fixation devices.

There are over 3 million bone fractures in the United States annually; over 30% of which require internal mechanical fixation devices to aid in the healing process. The current standard material used is a metal plate that is implanted onto the bone. However, metal fixation devices have many disadvantages, namely stress shielding and metal ion leaching. This study aims to fix these problems of metal implants by making a completely biodegradable material that will have a high modulus and exhibit great toughness. To accomplish this, long-fiber poly-l-lactic acid (PLLA) was utilized in combination with a matrix composed of polycaprolactone (PCL) and hydroxyapatite (HA) nano-rods. Through single fibril tensile tests, it was found that the PLLA fibers have a Young's modulus of 8.09 GPa. Synthesized HA nanorods have dimensions in the nanometer range with an aspect ratio over 6. By dip coating PLLA fibers in a suspension of PCL and HA and hot pressing the resulting coated fibers, dense fiber-reinforced samples were made having a flexural modulus up to 9.2 GPa and a flexural strength up to 187 MPa. The flexural modulus of cortical bone ranges from 7 to 25 GPa, so the modulus of the composite material falls into the range of bone. The typical flextural strength of bone is 130 MPa, and the samples here greatly exceed that with a strength of 187 MPa. After mechanical testing to failure the samples retained their shape, showing toughness with no catastrophic failure, indicating the possibility for use as a fixation material. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1963-1971, 2017.

Bioinspired Interface Engineering in Elastomer/Graphene Composites by Constructing Sacrificial Metal-Ligand Bonds.

It remains a huge challenge to create advanced elastomers combining high strength and great toughness. Despite enhanced strength and stiffness, elastomeric nanocomposites suffer notably reduced extensibility and toughness. Here, inspired by the concept of sacrificial bonding associated with many natural materials, a novel interface strategy is proposed to fabricate elastomer/graphene nanocomposites by constructing a strong yet sacrificial interface. This interface is composed of pyridine-Zn(2+) -catechol coordination motifs, which is strong enough to ensure uniform graphene dispersion and efficient stress transfer from matrix to fillers. Moreover, they are sacrificial under external stress, which dissipates much energy and facilitates chain orientation. As a result, the strength, modulus, and toughness of the elastomeric composites are simultaneously strikingly enhanced relative to elastomeric bulk. This work suggests a promising methodology of designing advanced elastomers with exceptional mechanical properties by engineering sacrificial bonds into the interface.

Diamond tool wear in ultra-precision machining

Diamond has many outstanding properties, such as high hardness, great toughness, high capability up to a nanometric tool cutting edge, high thermal conductivity, low friction, and high wear resistance. Accordingly, it is employed as an efficient tool in ultra-precision machining (UPM). However, diamond tool wear (DTW) in UPM is an inevitable physical phenomenon and even a little DTW will produce a direct impact on nanometric surface roughness. With a focus on diamond’s physical characteristics, this paper looks at the current investigations of DTW and posits an improved understanding of DTW in UPM. Firstly, the differences in DTW caused by different workpiece materials are reviewed, as are the factors influencing DTW and its effects. Secondly, the DTW mechanisms are summarized, including DTW anisotropy, DTW features, and DTW behaviors, with diamond tool performances. Thirdly, DTW measuring, DTW monitoring, DTW controlling, and DTW modeling are introduced. Thirdly, different methods for DTW suppression are surveyed with a view to improving the cutting performance of diamond tools. Finally, the challenges and opportunities for DTW, which may be of particular interest for future studies, are discussed with several conclusions.

Bio-Inspired Hydrogen-Bond Cross-Link Strategy toward Strong and Tough Polymeric Materials

It remains a huge challenge to create advanced polymeric materials combining high strength, great toughness, and biodegradability so far. Despite enhanced strength and stiffness, biomimetic materials and polymer nanocomposites suffer notably reduced extensibility and toughness when compared to polymer bulk. Silk displays superior strength and toughness via hydrogen bonds (H-bonds) assembly, while cuticles of mussels gain high hardness and toughness via metal complexation cross-linking. Here, we propose a H-bonds cross-linking strategy that can simultaneously strikingly enhance strength, modulus, toughness, and hardness relative to polymer bulk. The H-bond cross-linked poly(vinyl alcohol) exhibits high yield strength (140 MPa), reduced modulus (22.5 GPa) in nanoindention tests, hardness (0.5 GPa), and great extensibility (40%). More importantly, there exist semiquantitive linear relationships between the number of effective H-bond and macroscale properties. This work suggests a promising methodology of designing advanced materials with exceptional mechanical by adding low amounts (1.0 wt %) of small molecules multiamines serving as H-bond cross-linkers.

Effect of interpass temperature on microstructure, impact toughness and fatigue crack propagation in joints welded using the GTAW process on steel ASTM A743-CA6NM

Mainly due to their great toughness, martensitic stainless steels are used for manufacturing hydraulic turbines. However, these steels have some restrictions regarding regions recovered by welding, mainly due to the formation of non-quenched martensite, which causes a reduction in toughness. Considering repair of hydraulic turbines, there is a great interest in developing welding procedures that increase impact toughness and avoid post-welding heat treatment (TTPS). This study aims to analyse the influence of interpass temperature on microstructure, impact toughness and fatigue crack propagation in multipass welded joints on martensitic stainless steel CA6NM, using AWS410NiMo filler metal and the gas tungsten arc welding (GTAW) process. In the sample with interpass temperature of 80°C, influence of the interpass temperature on the formation of ferrite δ, with intragranular formation in the two-phase δ field, was observed, while in the sample welded at 150°C, the formation of ferrite δδ occurred mainly in the single-phase field. The change in the formation of ferrite δ, with the low interpass temperature, promoted an increase in impact toughness and a decrease in the fatigue crack propagation when compared with the sample welded with a higher interpass temperature. The results obtained indicate that the TIG process is an excellent alternative for the repair of CA6NM steel, with a significant influence from the interpass temperature.

Long Term High-Temperature Environmental Effect on Impact Toughness in Austenitic Alloys

Structural integrity is crucial for the safety of power plants with higher efficiency to meet the increasing global energy consumption. High-temperature environment will demand not only improved high-temperature corrosion resistance but also a maintained sufficient toughness. This study investigates how long term high-temperature environment influence the impact toughness of two austenitic stainless steels (AISI 304 and Sandvik SanicroTM 28) and one nickel-bas alloy (Alloy 617). Alloy 617 has shown increasing impact toughness with both increasing temperature and time, up to 700°C and 3 000 hours, while the two austenitic stainless steels have shown the opposite for the same conditions. At 10 000 hours the impact toughness of Alloy 617 has decreased but the alloy still possess great toughness. Both austenitic stainless steels show embrittlement due to brittle σ-phase and Alloy 617 seems to gain good impact toughness performance from small evenly distributed precipitates.

Block architecture influence on the structure and mechanical performance of drawn polyurethane elastomers

Some natural biopolymers such as spider silk exhibit superb mechanical properties, characterised by their great toughness. Synthetic polyurethane (PU) copolymers also endow great toughness but lack silk's stiffness and strength. The aim of this work was to elucidate the role of segment block architectural features that influence PU stiffness and strength after cold drawing. For this purpose PUs with varied soft segment character, crystalline versus rubbery, as well as with different hard segment chemistries, 4,4′‐diphenylmethane diisocyanate/1,4‐butanediol versus 1,6‐hexamethylene diisocyanate/1,4‐butanediol, were synthesised by a two‐step polymerisation method. We found that the architecture of both block segments has a dramatic influence on drawn PU mechanical performance, in which PUs with crystallisable soft segments and crystalline hard segments are shown to have a greater impact on developing stiffer and stronger materials. © 2013 Society of Chemical Industry

On the “Ceramic Constrained by Metal” Composite Materials

Ceramics are widely used in every field of contemporary industrial because of its many excellent properties. However, its mechanical property is great brittleness and small toughness for the characteristics of internal chemical bond, which restricts its application range to a large extent. Therefore, how to improve mechanical properties of ceramic materials has been attracted a great attention in the relevant area. For ceramics using at room temperature, a method which can avoid brittle failure by metal confinement outside of ceramics is given. And the feasibility of this method is discussed. Three point bending tests were conduct on ZrO2 ceramics with and without lateral confinement separately. Base on the much of experimental conclusion, the bending strength of ceramic with lateral confinement was improved largely.

Rotary Ultrasonic Machining of Sapphire: Feasibility Study and Designed Experiments

Sapphire, widely used in high-speed integrated-circuit chips, thin-film substrates, and various electronic components, is regarded as one of the most difficult to cut materials owing to its great hardness and low fracture toughness. Rotary ultrasonic machining (RUM) has been regarded as an effective processing method for hard and brittle materials. In this paper, RUM process is introduced into the drilling of sapphire for the first time. The feasibility to machine sapphire using RUM is studied. Moreover, results of a designed experimental study into RUM of sapphire are presented to discuss the main effects as well as interaction effects of process parameters (ultrasonic power, spindle speed, and feedrate) on outputs. The process outputs investigated include cutting force and edge chipping size.

Special Issue on Difficult-to-Cut Materials

Nickel-based super alloys, Ti alloys, CFRP, hardened steels, etc., are widely used in aerospace, automobile, chemical, and other industries because of such superior properties as high operating temperature, superior specific strength, outstanding hardness and/or great toughness. These properties, however, also present difficulties in machining, cutting temperature, cutting, adhesiveness, chip controllability and wear. Other distinguishing properties include instable tool life, surface finishing and chip control in machining. This means that the stabilization of cutting is very important, especially when machining NC machine tools. Metal machining involves many parameters, such as cutting tools, cutting oil, cutting speed, feed rate, depth of cut, and machine use. A metal machining engineer therefore must decide all of these parameters to ensure their most suitable values under boundary conditions such as machining time, accuracy and the surface roughness of machined parts. Machining, especially of difficult-to-cut materials, is an optimization problem occurring under specified boundary conditions. Choosing machining parameters, including tool geometry and the most favorable features of work materials, must thus be figured out and optimum cutting conditions selected based both on metal machining theory and on practice. This special issue covers recent development in the machining of difficult-to-cut materials, including hardened steel, stainless steel, titanium alloys, Inconel 718, hard brittle materials and CFRP. All of the papers in this special issue are of great interest and value in machining these materials. We thank the authors for their invaluable submissions and the reviewers for their earnest efforts, without which this special issue would not have been possible.