Crack Propagation Resistance Research Articles

Toughing epoxy nanocomposites with Graphite-Nanocellulose layered framework

Epoxy nanocomposites hold immense promise for advanced high-performance applications in coatings, adhesives, and fiber-reinforced composite matrices. However, their widespread use is hindered by low fracture toughness, attributed to highly cross-linked network structure. Here, this study presents a synergistic manufacturing strategy combining ultrasonic graphite-nanocellulose assembly and bidirectional freeze casting to fabricate epoxy nanocomposites with remarkable layered architectures. Subsequent infiltration and curing with epoxy prepolymer produce nanocomposites exhibiting a fracture toughness 4.67 times higher than pure epoxy. Both experimental and theoretical analyses demonstrate the nanocomposite's superior crack propagation resistance, attributable to a range of synergistic toughening mechanisms. These include robust interfacial bonding and mechanical interlocking, which arise from fiber pull-out/flake fracture effects, effectively impeding crack growth. Additionally, the distinctive layered architecture promotes tortuous crack pathways, optimizing fracture energy dissipation. This work offers pivotal insights into structure–property relationships, paving the way for the design of next-generation nanocomposites with tailored, superior mechanical performance.

Modified Paris law for mode I fatigue fracture of concrete based on crack propagation resistance

To characterize mode I fatigue fracture of concrete, the Paris law has been widely applied. However, due to the quasi-brittle properties of concrete, it has been found that the empirical constants in the model are dependent on the size of the specimen and the level of the fatigue load. In addition, the crack propagation resistance under cyclic loading introduced in the existing modified Paris law is difficult to determine. In this study, the crack propagation resistance of concrete under static loading is introduced into the Paris law, and a new modified Paris law is proposed. The validity of the model is confirmed by the reasonable correspondence between the prediction of the mode I fatigue lives of TPB beams and the experimental data. The proposed model offers several advantages. First, the empirical constants remain independent of the specimen depth, initial crack length to depth ratio, and fatigue load level. Additionally, the introduced crack propagation resistance is easier to determine. The study concludes that if the initial fracture toughness, unstable fracture toughness, and empirical constants in the model are predetermined, it can forecast the mode I fatigue fracture life of concrete with diverse geometric dimensions and fatigue load levels. This prediction contributes to the overall safety assessment of concrete structures subjected to fatigue loading.

Microstructural influences on simultaneous strength and fatigue crack resistance in advanced high-strength steels

In this study, we investigate the relation between microstructure and fatigue crack propagation mechanisms in three commercial hot-rolled thick-plate advanced high-strength steels (AHSSs), namely 800CP, 700MC, and 700MCPlus, and compare them with a conventional high-strength low-alloy (HSLA) steel, 500MC, commonly used in heavy-duty vehicle chassis production. Tensile testing, and fatigue crack growth rate (FCGR) assessments have been conducted, and mechanisms controlling the performance of these steels are comprehensively examined through microstructure characterization before and after fatigue testing. Notably, FCGR results reveal that, despite having the highest yield strength among the investigated steels, 700MCPlus exhibits the slowest FCGR in both near-threshold and stable crack growth regimes. This improved fatigue crack propagation resistance of 700MCPlus in terms of its threshold stress intensity factor range (ΔKth) is attributed to its unique texture, which restricts slip activity, and the presence of martensite at grain boundaries, contributing to fatigue crack deflection. This martensite-induced crack deflection becomes more significant in the stable crack growth regime, where fatigue crack primarily propagates intergranularly as the stress intensity factor range (ΔK) increases. These mechanistic findings offer new design possibilities for AHSSs, combining excellent strength and fatigue performance.

Processing–microstructure–fracture toughness relationships in PP/EPDM/SiO2 blend‐nanocomposites: Effect of mixing sequence

AbstractThis study investigates the mechanical properties and fracture behavior of polypropylene (PP)‐based blend‐nanocomposites comprising 30 wt.% ethylene–propylene–diene monomer (EPDM) and 5 wt.% SiO2 nanoparticles. Different mixing sequences were employed to prepare the nanocomposites, and the resulting morphology development and dispersion states of modifiers were analyzed. Mechanical performance of the nanocomposites was evaluated through quasi‐static and high‐speed dynamic fracture tests. The dispersion and distribution of SiO2 nanoparticles within the nanocomposites were significantly influenced by the mixing protocol. In impact fracture tests, the presence of nanoparticles exhibited a beneficial efffect on fracture energy, demonstrating a synergistic toughening effect of the soft EPDM and rigid SiO2 particles. Conversely, adverse effects were observed in quasi‐static tests. Essential work of fracture (EWF) parameters indicated an increase in the yielding component and a decrease in the necking‐to‐tearing component with SiO2 incorporation into the PP/EPDM blends. During impact loadings, the highest improvement in crack propagation resistance was observed in nanocomposites with nanoparticles localized around the rubbery domains forming a network‐like structure of EPDM/SiO2‐nanoparticles. Morphologies where rubber domains and nanoparticles were separately distributed in the PP matrix resulted in the lowest fracture parameters. Energy dissipation mechanisms were elucidated, revealing multiple void formation followed by matrix shear yielding as the primary source under both quasi‐static and impact fracture conditions. In the latter case, stress‐concentrating percolated structures in the PP matrix facilitated the nucleation of dilatational bands evolving into highly stretched void‐fibrillar structures upon further loading. These findings contribute valuable insights into tailoring nanocomposite morphologies for enhanced mechanical performance in different loading scenarios.Highlights Fracture behavior of PP/EPDM/SiO2 ternary systems was evaluated by EWF methodology and Izod impact test. Rubber particles surrounded by silica nanoparticles led to a percolated morphology and as a result to superior impact resistance. EWF parameters were mostly controlled by the tearing‐related parts regardless of phase morphology. The impact toughness was mainly controlled by the dispersion and distribution characteristics of the SiO2 nanoparticles.

Resistance of fatigue crack propagation induced by large α colony in a Ti‐Al‐V‐Mo‐Zr alloy

AbstractFor Ti alloys used in oil drilling pipe, the fatigue crack propagation (FCP) resistance is one of the key properties for petroleum industrial applications. In this work, the fatigue crack propagation behaviors of bimodal, equiaxed, lamellar, and Widmanstatten microstructures have been systematically investigated and characterized by SEM and EBSD. The results show that the Widmanstatten microstructure containing α colonies has higher yield strength (877 MPa), moderate elongation (9.3%), and better FCP resistance compared to other specimens. During the process of crack propagation, the large α colonies can effectively deflect the cracks and induce secondary cracks, which significantly impedes the main crack propagation. Additionally, tensile twinning can occasionally occur within the large α colony along the crack, improving the plasticity of the crack tip and resulting in a decrease in fatigue crack propagation rate (FCPR).

Self-heating and fatigue crack growth behavior of reinforced NR/BR nanocomposites with different blending ratio

Fatigue crack growth and dissipative self-heating due to viscoelasticity are crucial properties of rubber materials under dynamic service conditions. Systematic evaluation of the thermo-mechanical coupled fatigue properties with suitable lab testing methods could contribute to the development of long-lasting and robust elastomer materials. In this work, on the one hand, the hysteresis energy density, thermal conductivity, and surface temperature rise, which are closely related to the self-heating generation rate, heat transfer rate and heat build-up of the carbon black reinforced seven different natural rubber (NR) and polybutadiene rubber (BR) blends were measured. A thermo-mechanical coupling simulation method was used to reproduce the experimental observation. On the other hand, the fatigue threshold (T0), critical tearing energy (Tc), and fatigue crack growth rate (FCGR) under different tearing energy were investigated by using the advanced rubber fatigue instruments. The Lake-Lindley model was utilized to describe the rubber fatigue responses from the intrinsic strength to the ultimate strength. The results show that the dissipative self-heating of NR/BR:30/70 blend is the most obvious one, which could be well explained by the simulation results. The T0 shows an upward trend while Tc shows a downward trend with the increasing blend ratio of BR. The existence of carbon black fillers showed tiny effect on T0 of NR, but significantly enhanced the T0 of BR. The FCGR of reinforced NR/BR nanocomposites have Lake-Lindley law responses that cross over each other. Therefore, which rubber material is superior to others in resisting crack propagation depends on the magnitude of the input tearing energy.

The Variation Patterns of the Martensitic Hierarchical Microstructure and Mechanical Properties of 35Si2MnCr2Ni3MoV Steel at Different Austenitizing Temperatures.

This study investigates the influence of varying austenitizing temperatures on the microstructure and mechanical properties of 35Si2MnCr2Ni3MoV steel, utilizing Charpy impact testing and microscopic analysis techniques such as scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The findings reveal that optimal combination of strength and toughness is achieved at an austenitizing temperature of 980 °C, resulting in an impact toughness of 67.2 J and a tensile strength of 2032 MPa. The prior austenite grain size initially decreases slightly with increasing temperature, then enlarges significantly beyond 1100 °C. The martensite blocks' and packets' structures exhibit a similar trend. The proportion of high-angle grain boundaries, determined by the density of the packets, peaks at 980 °C, providing maximal resistance to crack propagation. The amount of retained austenite increases noticeably after 980 °C; beyond 1200 °C, the coarsening of packets and a decrease in density reduce the likelihood of trapping retained austenite. Across different austenitizing temperatures, the steel demonstrates superior crack initiation resistance compared to crack propagation resistance, with the fracture mode transitioning from ductile dimple fracture to quasi-cleavage fracture as the austenitizing temperature increases.

A Highly Damping, Crack‐Insensitive and Self‐Healable Binder for Lithium‐Sulfur Battery by Tailoring the Viscoelastic Behavior

AbstractBinder plays an important role in maintaining the integrity of sulfur electrode in lithium‐sulfur (Li‐S) battery. However, cracks are easily generated inside the electrode and compromise its performance due to the volume change of sulfur during redox reaction and continuous vibration originated from the external environments. It is a challenge yet crucial to develop tough binders with crack‐insensitivity and damping performance. Herein, a polymeric binder is designed with special viscoelastic behavior by tailoring its electrolyte‐philic and electrolyte‐phobic domains. The loss modulus of the binder is regulated to be highly close to its storage modulus within a wide range of frequency, generating an ultra‐high loss factor and equilibrium of viscosity‐elasticity. Based on such rheological behavior, the binder holds 1) high damping ability across a wide frequency to suppress crack generation, 2) high toughness with crack blunting behavior to resist crack propagation, 3) efficient healing capability to repair the cracks. Besides, the pendant zwitterionic groups can immobilize the lithium polysulfides and promote ion transfer. Benefiting from these advantages, the obtained Li‐S battery delivers high specific capacity with considerable capacity retention after long‐term cycling. The viscoelastic design and crack management strategy illustrated here would provide new insights into the binder design.

Microstructure and mechanical properties of a dilute Mg-Gd-Y-Zr alloy fabricated using wire-arc directed energy deposition additive manufacturing

Mg-Gd-Y-Zr is an important lightweight material in the aerospace field. However, the engineering applications of large-scale Mg-Gd-Y-Zr alloy components are significantly limited by macrosegregation and microstructure coarsening during the casting process. In recent years, wire-arc directed energy deposition (DED), which has high design and manufacturing freedom, provides a new route to manufacture large-scale metal parts. In this work, a dilute Mg-3.2Gd-0.6Y-0.5Zr (wt.%) alloy, which had a degree of alloying comparable to AZ31 commercial alloys, was fabricated using a wire-arc DED process based on tungsten inert gas (TIG) welding, the microstructure evolution, tensile properties, and impact toughness were investigated. Due to the multiple grain refinement effects, the DED sample displayed a fine-grain structure (12.3 ± 7.4 μm), which was comparable to that of the wrought counterpart. Combined with the ductilizing effects of the fine grain and the Gd/Y solutes, the DED sample achieved a high ductility, which was better than most reported additive-manufactured Mg alloys as well as wrought Mg alloys. The good plastic deformation capacity also endowed the DED sample with good crack propagation resistance under dynamic impact load. We hope this work can help guide the further development of high-performance Mg alloys that are specially designed for the wire-arc DED additive manufacturing process.

Preparation and Characterization of Multilayer NiTi Coatings by a Thermal Plasma Process.

The deposition of multilayer coating of NiTi is carried out by a thermal plasma spraying process on a stainless steel substrate. The deposition of melted NiTi particles creates an adhesion layer on the substrate with the subsequent formation of multilayer coating with a certain thickness. Six layers of coating are created to achieve a certain thickness in terms of the sprayed sample. This paper aims to investigate multilayer NiTi coatings created through a thermal plasma process. The key variable feed rate was considered, as well as its effect on the microstructure characteristics. The shape memory effect associated with the coating properties was analyzed in detail. The variable feed rate was considered one of the most important parameters in the thermal plasma spraying process due to its ability to control the quality and compactness of the coating structure. The coatings were characterized by examining their microstructure, thermal, chemical, and microhardness. The indent marks were made/realized along the cross-section surface for the analysis of crack propagation resistance and wear properties. The coating's surface did not display segmentation crack lines. Nevertheless, the cross-sectional surfaces showed evidence of crack lines. There were eutectic zones of the interlamellar structure observed in the structure of the coating. The plasma-sprayed samples from thermo-mechanical analysis of the hysteresis curve provide strong confirmation of the shape memory effect.

Improving the mechanical property of the castables bonded with hydratable magnesium carboxylate by incorporating MgO fumes

AbstractPrevious studies have indicated that hydratable magnesium carboxylate (HMC) exhibits potential as an MgO‐based binder, but its limited medium‐temperature strength has hindered its widespread industrial application. In this study, the incorporation of MgO fumes into castables is intended to react with microsilica to form magnesium–silicate–hydrate (M–S–H), and the synergistic effect of HMC and M–S–H is anticipated to improve the mechanical properties of castables at intermediate temperatures. The effects of MgO fumes on the properties of HMC‐bonded castables were comprehensively investigated. The results demonstrate that incorporating MgO fumes into castable serves multiple functions. The ionized MgOH+ from MgO fumes hinders the hydration process of HMC, prolonging the final setting time from 13 to 98 min and improving the workability of castables. The incorporation of MC‐1100 enhanced mechanical properties at medium temperature due to the synergistic effects of brucite, HMC, and M–S–H. Specifically, the CMOR increased 20% after sintering at 800°C. Furthermore, adding MC‐1100 increases the residual strength rate of castable by 10% compared to those without MgO fumes. This can be attributed to enhanced spinel formation resulting from adding MgO fumes that improves elastic modulus and reduces elastic strain energy generation during thermal shock, thus increasing crack propagation resistance.

Effect of Single Crystal Growth and Solidification Grain Boundaries on Weld Solidification Cracking Behavior of CMSX-4 Superalloy

Single-crystal superalloys have been popularly employed in high-temperature parts of gas turbines, such as blades. However, the welds of such alloys are highly susceptible to solidification cracking, which limits their applicability to high-temperature turbine blades. In this study, the effects of characteristics of weld solidification on solidification cracking susceptibilities (solidification brittle temperature range, BTR) were fundamentally investigated for the CMSX-4 single-crystal superalloy. We applied a transverse-Varestraint test procedure for both the linear and oscillated arc welds by changing the weld solidification characteristics, such as the degree of single crystal growth and formation of solidification grain boundaries. The BTR for the CMSX-4 alloy is 336 K for linear welding condition, whereas the values are 434 K and 342 K for 0.6 and 1.5 Hz oscillated welds. Interestingly, the BTR continuously increases with the weld oscillation frequency. By contrast, almost no changes in the weld mushy-zone temperature range are theoretically calculated for each welding condition via the diffusion-controlled Scheil model. The mechanism underlying the increase in BTR under oscillation welding is clarified based on the relationship between the achievement ratio of the weld single crystal growth and fraction of high-angle (>15<sup>o</sup>) solidification boundaries, which affect severe dendrite coalescence undercooling. The lower fraction of the high-angle weld solidification grain boundaries attributed to the superior achievement ratio of weld single crystal growth, which reduces the dendrite coalescence undercooling and BTR. Consequently, it enhances the solidification crack propagation resistance.

The columnar dendrite and equiaxed dendrite transformation of high Nb-TiAl alloy by laser-directed energy deposition

Laser-directed energy deposition (LDED) is a significant method for shaping high Nb-TiAl alloys. The dendrite type has an impact on the mechanical properties of parts fabricated with LDED. This study establishes a dendrite transformation model for the alloy. The refinement mechanism of microstructure and the strengthening mechanism of high-temperature mechanical properties are analyzed through experiment and simulation. The results show that the scanning rate has a significant influence on the dendrite type. Modifying the scanning rate brings about a gradual decrease in the G/R (where G denotes temperature gradient and R is the growth rate) value of the molten pool, and a concurrent gradual increase in the value of G×R. These changes facilitate the transformation of columnar dendrites into equiaxed dendrites. Furthermore, the lamellar colony size is reduced by 72.8% and the tensile strength at 900 °C is increased by 16.2%. Microstructure refinement is the primary reason for the enhancement of high-temperature tensile characteristics, with dislocations and deformation twins also contributing to crack propagation resistance.

Factors Affecting the Cracking Resistances of a Spring Steel Tempered at Different Temperatures

Cracking resistance is vital to the practical application of spring steels, which consists of fracture toughness (KIC) under the quasistatic loading condition and fatigue crack propagation (FCP) resistance under the cyclic loading condition. In the present study, the relation between the KIC/FCP resistance and microstructure of the 50CrMnSiVNb spring steel tempered at various temperatures is studied. In the results, it is shown that the dislocation density is the main factor influencing the KIC and FCP resistances, and the carbide size/quantity and morphology can also affect the KIC and FCP resistances. Thus, reducing the dislocation density is the most effective method to enhance the cracking resistance of the investigated steel. Moreover, decreasing the aspect ratio and obtaining a moderate size of tempered carbides are also beneficial to the cracking resistance. In addition, free hydrogen atoms can cause intergranular fracture on the fracture surface, worsening the FCP rate. To enhance the FCP resistance, smelting processes need to be improved to reduce the hydrogen content of the investigated steel.

Design of Fatigue‐Resistant Hydrogels

AbstractHydrogels are made tough to resist crack propagation. However, for seamless integration into devices and machines, it necessitates robustness against cyclic loads. Central to this objective is enhancing fatigue resistance, an indispensable attribute facilitating the optimal performance of hydrogels within a multitude of biological contexts, spanning various plant and animal tissues, as well as diverse biomedical and engineering areas. In this review, recent research concerning the fatigue behavior of hydrogels, presenting a comprehensive consolidation of the inherent mechanisms that underpin diverse strategies aimed at fortifying fatigue resistance, is summarized. A critical facet in the architectural blueprint of fatigue‐resistant hydrogels is emphasized, involving the imposition of spatial constraints upon the main chains at the crack tips, thereby effectuating a protracted delay in their fracture initiation during prolonged cyclic loading. The integration of multiscale mechanisms encompassing networks, interactions, media, and structures stands as a pivotal factor in the design of fatigue‐resistant hydrogels. It is hoped that the review will considerably propel the pragmatic deployment of fatigue‐resistant hydrogels across a diverse array of applications, thus catalyzing advancements in multiple fields.

Water vapor assisted aramid nanofiber reinforcement for strong, tough and ionically conductive organohydrogels as high-performance strain sensors.

Conductive organohydrogels have gained increasing attention in wearable sensors, flexible batteries, and soft robots due to their exceptional environment adaptability and controllable conductivity. However, it is still difficult for conductive organohydrogels to achieve simultaneous improvement in mechanical and electrical properties. Here, we propose a novel "water vapor assisted aramid nanofiber (ANF) reinforcement" strategy to prepare robust and ionically conductive organohydrogels. Water vapor diffusion can induce the pre-gelation of the polymer solution and ensure the uniform dispersion of ANFs in organohydrogels. ANF reinforced organohydrogels have remarkable mechanical properties with a tensile strength, stretchability and toughness of up to 1.88 ± 0.04 MPa, 633 ± 30%, and 6.75 ± 0.38 MJ m-3, respectively. Furthermore, the organohydrogels exhibit great crack propagation resistance with the fracture energy and fatigue threshold as high as 3793 ± 167 J m-2 and ∼328 J m-2, respectively. As strain sensors, the conductive organohydrogel demonstrates a short response time of 112 ms, a large working strain and superior cycling stability (1200 cycles at 40% strain), enabling effective monitoring of a wide range of complex human motions. This study provides a new yet effective design strategy for high performance and multi-functional nanofiller reinforced organohydrogels.

Effect of cathodic protection on the corrosion fatigue crack growth behavior and fatigue life of XS-grade shipbuilding steel

Shipbuilding steels are subjected to corrosion fatigue damage phenomena due to conjoint effects of cyclic loading by sea waves and corrosive seawater environment, which often leads to premature failure of ship hull structures. In practice, the impressed current cathodic protection (ICCP) technique is applied to mitigate ship hull corrosion by electrochemically making it cathodic. It is implemented by impressing a direct current to minimize the electrode potential to a predefined protection potential. It is significant to study the effect of ICCP on the corrosion fatigue crack growth rate (CFCGR) behavior and fatigue life assessment of ship hull structures. In this study, CFCGR behavior of high-strength XS-grade shipbuilding steel was investigated in unprotected freely corroding (FC) and protected ICCP (at – 800 mV) conditions using compact-tension specimens at 0.1 Hz frequency in artificial seawater (3.5 wt.% NaCl solution). After crack-closure corrections, it was found that the ICCP-protected specimen (∆KTH = 18 MPa √m) exhibited higher sub-critical or threshold corrosion fatigue crack propagation resistance as compared to the FC specimen (∆KTH = 14 MPa √m). Fractography of the FC specimen revealed the debonding of non-metallic inclusions and formation of micro-pits/secondary cracks as dominant damage mechanisms. ICCP-protected specimen exhibited a signature pattern of parallel secondary cracks and a proportional increase in their density with increasing stress intensity levels during primary crack growth. This fracture morphology indicated the primary-crack branching and further arrest, leading to retarded crack growth rates under ICCP-protection. Fatigue life analysis also confirmed this finding, where the beneficial ICCP-protection effect resulted in at least two times enhancement in fatigue lives from the unprotected FC condition.

New insights into pure zwitterionic hydrogels with high strength and high toughness.

Zwitterionic hydrogels are electrically neutral materials with both cationic and anionic groups that impart excellent anti-fouling properties and ion channel orientations. However, pure zwitterionic hydrogels generally exhibit low strength and toughness. In this study, it has been discovered that polymerizable zwitterionic monomers in aqueous solution exhibit a unique liquid-liquid phase separation phenomenon at a high monomer concentration of ≥50 wt%, resulting in pure and commercial zwitterionic hydrogels with high compressive strength (6.5 MPa) and high toughness (2.12 kJ m-2). This phase separation and the corresponding aggregations might be caused by strong dipole-dipole interactions among residual zwitterionic monomers under the lack of free-water condition. The synergistic effect of liquid-liquid phase separation and polymer entanglement enhances the mechanical strength, toughness, self-recovery, and anti-freezing properties of pure polyzwitterionic hydrogels. Moreover, the high fracture energy of highly elongated yet tough polyzwitterionic hydrogels facilitates the development of high crack propagation resistance, which supports an expanded role in tissue engineering, soft flexible devices, and electronics applications with improved durability. A wide range of applications for the proposed polyzwitterionic hydrogels is demonstrated by the development and testing of a strain sensor and a triboelectric nanogenerator device. Our findings provide novel insights into the network structure of pure polyzwitterionic hydrogels.

Development of high strength and lightweight Ti6Al4V5Cr alloy: Microstructure and mechanical characteristics

This article explains development of high strength and lightweight Ti6Al4V5Cr alloy by μ-plasma powder additive manufacturing (μ-PPAM) process for automotive, aerospace, military, dies and moulds, and other similar applications. Microstructure, formation of phases, porosity, microhardness, tensile properties, abrasion resistance, and fracture toughness of multi-layer deposition of Ti6Al4V5Cr alloy are studied and compared with Ti6Al4V alloy. Results reveal that the presence of chromium in Ti6Al4V5Cr alloy refined the grains of its β-Ti and α-Ti phases, increased volume % of β-Ti phase, and promoted formation of its equiaxed grains. It also increased tensile strength, microhardness, abrasion resistance, and fracture toughness of Ti6Al4V5Cr alloy. It enhanced solid solution strengthening and formed higher hardness imparting intermetallic Cr2Ti phase and changed fracture mode to mixed ductile and brittle mode with larger size dimples, cleavage facets, and micropores. But it decreased formation temperature of β-Ti phase and % elongation as compared to Ti6Al4V alloy. Chromium and vanadium content in β-Ti phase of Ti6Al4V5Cr alloy is 7 % and 2.1 % more than its α-Ti phase. This study demonstrates that inclusion of limited amount of chromium content to Ti6Al4V5Cr alloy by μ-PPAM process is very beneficial to enhance microstructure, mechanical properties, crack propagation resistance, and abrasive wear resistance of the Ti6Al4V5Cr alloy. It makes Ti6Al4V5Cr alloy very useful in many commercial applications that require higher strength than Ti6Al4V alloy along with lightweight requirement.

Assessment of crack propagation resistance in SMA mixtures with reclaimed asphalt pavement

Konieczność okresowej wymiany warstw ścieralnych w tym z mieszanek typu SMA wiąże się z możliwością pozyskania i ponownego wykorzystania wysokiej jakości destruktu asfaltowego. Dotychczas problem stosowania destruktu oraz granulatu asfaltowego do mieszanek typu SMA nie był przedmiotem szerokich analiz i badań. Wdrażanie zasad gospodarki o obiegu zamkniętym wymusi w najbliższym czasie upowszechnienie stosowania granulatu asfaltowego również do mieszanek typu SMA. W procesie wymiany warstwy ścieralnej nowa mieszanka mineralno-asfaltowa układana jest na istniejącej warstwie wiążącej, w której na skutek wcześniejszej eksploatacji mogą występować m.in. mikrospękania, które w okresie dalszego użytkowania nawierzchni będą propagować również do nowo wykonanej warstwy ścieralnej. Mieszanka SMA powinna zatem charakteryzować się odpornością na propagację spękań z niższych warstw asfaltowych. Zastosowanie w mieszance SMA materiału z recyklingu, zawierającego postarzone lepiszcze asfaltowe może przyczyniać się do zmniejszenia odporności na pękanie. Założono, że właściwości mieszanki mineralno-asfaltowej mogą być kształtowane m.in. poprzez modyfikację parametrów procesu produkcyjnego mieszanki. Analizie poddano wpływ wybranych warunków technologicznych wytwarzania mieszanek SMA z granulatem asfaltowym na ich odporność na propagacje spękań ocenianą metodą SCB. Badaniom poddano dwie mieszanki mineralno-asfaltowe typu SMA 11 o zawartości granulatu asfaltowego 20% oraz 40% m/m wytwarzane w technologii dozowania granulatu asfaltowego na gorąco. Na podstawie analizy uzyskanych wyników wykazano, że zarówno przyjęty schemat dozowania składników mieszanki, jak i zawartość granulatu asfaltowego mają istotny wpływ na uzyskiwane wartości parametrów charakteryzujących odporność na pękanie mieszanki mineralno-asfaltowej.