High Fracture Stress Research Articles

Experimental study on compression mechanical properties of functionally graded shape memory alloys

Functionally graded shape memory alloy (FG-SMA) hold considerable promise for diverse applications in aerospace and micro electro mechanical system (MEMS) fields, owing to their elevated ceramic hardness and distinctive phase transition characteristics. To investigate the mechanical properties and phase transition behaviors of FG-SMA, an FG-SMA specimen was fabricated for the first time using the spark plasma sintering and ball-mill mixing method. Subsequently, microstructure, phase transformation, hardness, compression fracture and shape memory effect testing experiments were carried out. The results revealed a microstructure of the FG-SMA without noticeable pores in the alumina content range of 0.1% to 0.6%. Alumina particles were effectively integrated into the NiTi matrix, enhancing the FG-SMA’s compressive strength. Varied alumina gradients in the FG-SMA cross-section led to distinct phase transitions. The addition of alumina increased the hardness of the NiTi matrix, resulting in higher fracture stress and strain in the FG-SMA. The elastic recovery strain of FG-SMA augmented with increasing alumina content, although the recoverable strain associated with the shape memory effect gradually decreased. This study provides valuable insights for the preparation, optimization, and practical applications of FG-SMAs. At the same time, the research in this article can lay an experimental foundation for the application of FG-SMA in the field of aerospace and MEMS.

Healable, Recyclable, and Ultra-Tough Waterborne Polyurethane Elastomer Achieved through High-Density Hydrogen Bonding Cross-Linking Strategy.

With the increasing popularity of elastomers in industry and daily life, their high performance and functionality have attracted widespread attention. However, it is a great challenge for them to possess both high mechanical properties and excellent healing and recovery capabilities due to the limitations of the preparation methods and the intrinsic microstructure of the elastomers. In this study, a strategy of ice-controlled interfacial stepwise cross-linking was proposed to prepare the waterborne polyurethane-based elastomers with ultrahigh-density hydrogen bonding interaction achieved by enhancing the utilization rate of phenol hydroxyl groups of tannic acid to the maximum extent. The elastomers have incredible mechanical properties, including ultrahigh toughness of 1.03 GJ m-3 (which represents the highest level among polyurethane elastomers prepared through common processing techniques to date), extremely high true fracture stress of ∼1.9 GPa, world-record fracture energy of 520 kJ m-2, and exciting multiple functional characteristics, such as highly efficient self-healing ability of 10 min, high resistance to physical damage and chemical corrosion, broad temperature and frequency damping effects, good shape memory effect, and excellent melt-processing recyclability and solvent recyclability. These robust multifunctional elastomers represent considerable potential in various fields, from defense and military industry and civil transportation to precision manufacturing, etc.

Strong, tough and anisotropic bioinspired hydrogels.

Soft materials are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a challenge to fabricate soft materials, such as hydrogels, with both high strength and toughness that are comparable to biological tissues. Inspired by the anisotropic structure of biological tissues, a novel solvent-exchange-assisted wet-stretching strategy is proposed to prepare anisotropic polyvinyl alcohol (PVA) hydrogels by tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and nanofibril formation". These hydrogels exhibit excellent mechanical properties, such as extremely high fracture stress (12.8 ± 0.7 MPa) and fracture strain (1719 ± 77%), excellent modulus (4.51 ± 0.76 MPa), high work of fracture (134.47 ± 9.29 MJ m-3), and fracture toughness (305.04 kJ m-2) compared with other strong hydrogels and even natural tendons. In addition, excellent conductivity, strain sensing capability, water retention, freezing resistance, swelling resistance, and biocompatibility can also be achieved. This work provides a new and effective method to fabricate multifunctional anisotropic hydrogels with high tunable strength and toughness with potential applications in the fields of regenerative medicine, flexible sensors, and soft robotics.

Quasi-static and dynamic compressive behavior of Zr-based bulk metallic glass with yttrium addition

The glass-forming ability, stress-strain relationships, and fracture characteristics of Zr60-xCu27Al8Fe5Yx (x =1, 3 and 5 at%) bulk metallic glasses are investigated under compressive strain rates ranging from 10−3 to 4 × 103 s−1 using a material testing system and split-Hopkinson pressure bar. The results show that yttrium addition leads to a broader supercooled liquid region (ΔTx) and a greater γ parameter (γ = Tx/(Tg+Tl)), particularly for x = 1 at%. For all of the tested alloys, the fracture stress increases with increasing strain rate, while the fracture strain decreases. The addition of 3 at% Y results in the highest fracture stress and an improved fracture strain. The fracture surface observations show that the fracture behavior of the BMGs is dominated by the strain rate, whereas the Y content plays only a minor role.

Effect of Homogenization on the Transformation Temperatures and Mechanical Properties of Cu15Ni35Hf12.5Ti25Zr12.5 and Cu15Ni35Hf15Ti20Zr15 High-Entropy Shape Memory Alloys.

The major challenge of high-temperature shape memory alloys (SMAs) is the collocation of phase transition temperatures (TTs: Ms, Mf, As, Af) with the mechanical properties required for application. Previous research has shown that the addition of Hf and Zr into NiTi shape memory alloys (SMAs) increases TTs. Modulating the ratio of Hf and Zr can control the phase transformation temperature, and applying thermal treatments can also achieve the same goal. However, the influence of thermal treatments and precipitates on mechanical properties has not been widely discussed in previous studies. In this study, we prepared two different kinds of shape memory alloys and analyzed their phase transformation temperatures after homogenization. Homogenization successfully eliminated dendrites and inter-dendrites in the as-cast states, resulting in a reduction in the phase transformation temperatures. XRD patterns indicated the presence of B2 peaks in the as-homogenized states, demonstrating a decrease in phase transformation temperatures. Mechanical properties, such as elongation and hardness, were improved due to the uniform microstructures achieved after homogenization. Moreover, we discovered that different additions of Hf and Zr resulted in distinct properties. Alloys with lower Hf and Zr had lower phase transformation temperatures, followed by higher fracture stress and elongation.

Biomechanical study of different fixation constructs for anterior column and posterior hemi-transverse acetabular fractures: a finite element analysis

BackgroundTo compare the biomechanical properties and stability, using a finite element model, of four fixation constructs used for the treatment of anterior column and posterior hemi-transverse (ACPHT) acetabular fractures under two physiological loading conditions (standing and sitting).MethodsA finite element model simulating ACPHT acetabular fractures was created for four different scenarios: a suprapectineal plate combined with posterior column and infra-acetabular screws (SP-PS-IS); an infrapectineal plate combined with posterior column and infra-acetabular screws (IP-PS-IS); a special infrapectineal quadrilateral surface buttress plate (IQP); and a suprapectineal plate combined with a posterior column plate (SP-PP). Three-dimensional finite element stress analysis was performed on these models with a load of 700 N in standing and sitting positions. Biomechanical stress distributions and fracture displacements were analysed and compared between these fixation techniques.ResultsIn models simulating the standing position, high displacements and stress distributions were observed at the infra-acetabulum regions. The degree of these fracture displacements was low in the IQP (0.078 mm), as compared to either the IP-PS-IS (0.079 mm) or the SP & PP (0.413 mm) fixation constructs. However, the IP-PS-IS fixation construct had the highest effective stiffness. In models simulating the sitting position, high fracture displacements and stress distributions were observed at the regions of the anterior and posterior columns. The degree of these fracture displacements was low in the SP-PS-IS (0.101 mm), as compared to the IP-PS-IS (0.109 mm) and the SP-PP (0.196 mm) fixation constructs.ConclusionIn both standing and sitting positions, the stability and stiffness index were comparable between the IQP, SP-PS-IS, and IP-PS-IS. These 3 fixation constructs had smaller fracture displacements than the SP-PP construct. The stress concentrations at the regions of quadrilateral surface and infra-acetabulum suggest that the buttressing fixation of quadrilateral plate was required for ACPHT fractures.

Non-Schmid Effect on the Fracture Behavior of Tungsten

The fracture process of tungsten is dominated by the competition mechanism between the plastic deformation and the crack propagation near the crack tip. The non-Schmid (NS) effect, which considers the contribution of non-planar shear stress on the screw dislocation motion, is known to significantly influence the plastic deformation of tungsten at low and medium temperatures. However, how the NS effect influences the crack-tip plasticity and the fracture behavior of tungsten remains to be answered. In this work, the coupled crystal-plasticity and phase-field model (CP-PFM) was adopted to study the influence of the NS effect on the plastic deformation of un-notched tungsten and the fracture process of pre-notched tungsten at different temperatures. It was found that the lower the temperature, the more significant the NS effect on tungsten plasticity, which manifests in the lower yield stress and more unsymmetrical plastic deformation when the NS effect is considered. In contrast, the NS effect displayed the most obvious effect on the fracture behavior of pre-notched tungsten in the medium temperature regime, which manifested as higher fracture stress, a more significant crack-tip shielding effect, different fracture morphology, and lower crack propagation speed. The brittle fracture response at low temperature was not affected too much by the existence of the NS effect.

Anisotropic crystal orientations dependent mechanical properties and fracture mechanisms in zinc blende ZnTe nanowires.

The orientations of crystal growth significantly affect the operating characteristics of elastic and inelastic deformation in semiconductor nanowires (NWs). This work uses molecular dynamics simulation to extensively investigate the orientation-dependent mechanical properties and fracture mechanisms of zinc blende ZnTe NWs. Three different crystal orientations, including [100], [110], and [111], coupled with temperatures (100 to 600 K) on the fracture stress and elastic modulus, are thoroughly studied. In comparison to the [110] and [100] orientations, the [111]-oriented ZnTe NW exhibits a high fracture stress. The percentage decrease in fracture strength exhibits a pronounced variation with increasing temperature, with the highest magnitude observed in the [100] direction and the lowest magnitude observed in the [110] direction. The elastic modulus dropped by the largest percentage in the [111] direction as compared to the [100] direction. Most notably, the [110]-directed ZnTe NW deforms unusually as the strain rate increases, making it more sensitive to strain rate than other orientations. The strong strain rate sensitivity results from the unusual short-range and long-range order crystals appearing due to dislocation slipping and partial twinning. Moreover, the {111} plane is the principal cleavage plane for all orientations, creating a dislocation slipping mechanism at room temperature. The {100} plane becomes active and acts as another fundamental cleavage plane at increasing temperatures. This in-depth analysis paves the way for advancing efficient and reliable ZnTe NWs-based nanodevices and nanomechanical systems.

Mechanical Properties of LPBF-Built Titanium Lattice Structures—A Comparative Study of As-Built and Hot Isostatic Pressed Structures for Medical Implants

We compare different lattice structures with various elementary cell sizes built by laser powder bed fusion with and without hot isostatic pressing as post treatment. Cylindrical lattice structures are mechanically tested upon static and dynamic load in order to achieve high elasticity, high fracture strength and a high number of cycles to failure with respect to applications as medical implants. Evaluating the Young’s modulus, a high stiffness for the body diagonal structure and a low fracture stress for the G-structure are measured. Hot isostatic pressing results in a higher Young’s modulus and is ambiguous in terms of fractural stress. While samples without hot isostatic pressing reveal a shear fracture, the hot isostatic pressed samples have a high ductile area where the lattice layers are wrapped and pressed into the underlying layers without a fracture. Under dynamic load, the samples without hot isostatic pressing mostly are unable withstand 106 cycles at typical loads of the human body. Hot isostatic pressing has no significant influence on the strength at high loads and low cycle numbers, but at low loads all samples survived 106 cycles. As a consequence, dode-thick and rhombic dodecahedrons with 2 mm and 1.5 mm lattice size after hot isostatic pressing are recommended for medical implants because of the high elasticity, high fracture stress and high resistance against dynamic loads, which fulfill implant requirements.

Effects of strain rate on properties of Zr–Cu–Al–Fe bulk metallic glasses with Nb addition

The glass-forming ability (GFA), stress-strain relationships, and fracture characteristics of Zr60-xCu27Al8Fe5Nbx (x = 0, 1, 3 and 5 at%) bulk metallic glasses (BMGs) are investigated over a wide compressive strain rate range of 10−3 to 4 × 103 s−1 using a material testing system (MTS) and split-Hopkinson pressure bar (SHPB). The addition of Nb is found to increase the supercooled liquid region (ΔTx) and parameter γ (γ = Tx/(Tg + Tl)) of the BMGs. For all of the tested alloys, the fracture stress increases with increasing strain rate. By contrast, the fracture strain decreases as the strain rate increases. The addition of 3 at% Nb results in the highest fracture stress and fracture strain. The fracture surface observations show that the fracture behavior of the BMGs is strongly related to the strain rate but is insensitive to the Nb content.

Hydrophobically Associated Functionalized CNT-Reinforced Double-Network Hydrogels as Advanced Flexible Strain Sensors

Hydrogels have gained the attention of researchers worldwide and can be widely applied for use in medical technologies in human health and in industrial applications such as robotics. However, producing a hydrogel with proper mechanical properties, low hysteresis energy, quick shape recovery, and long-range strain sensitivity is still an ongoing development. More development into hydrogel technology could also lead to an increase in the effectiveness and lifespan of artificial joint replacements. Our hydrogels can be incorporated into the development of highly sensitive strain sensors for wearable electronic devices. To work toward developing these technologies, multifunctional dual crosslinked hydrogels were developed using lauryl methacrylate, acrylamide, and acid-functionalized multiwalled carbon nanotubes (A-MWCNTs). Due to the dual crosslinking, the synthesized hydrogels display outstanding mechanical performance (high fracture stress, strain, toughness, and tensile strength). In shape recovery, the materials recover their original shape after compression and maintain hydrostaticity. A low hysteresis energy of 11.57 kJ m–3 makes it a suitable candidate for strain sensing with high sensitivity (GF = 9.2 at 500% strain) to monitor different human motions (wrist, neck movements, flexion of the fingers, swallowing, and during speaking). Additionally, due to its good mechanical properties, the cyclic stability was monitored up to 300 cycles and the hydrogel still was mechanically stable and had the fastest response–recovery time of less than 130 ms during mechanical performance studies. Our hydrogels can be used to develop highly sensitive strain sensors for wearable electronic devices.

Detecting upland glaciation in Earth’s pre-Pleistocene record

Earth has sustained continental glaciation several times in its past. Because continental glaciers ground to low elevations, sedimentary records of ice contact can be preserved from regions that were below base level, or subject to subsidence. In such regions, glaciated pavements, ice-contact deposits such as glacial till with striated clasts, and glaciolacustrine or glaciomarine strata with dropstones reveal clear signs of former glaciation. But assessing upland (mountain) glaciation poses particular challenges because elevated regions typically erode, and thus have extraordinarily poor preservation potential. Here we propose approaches for detecting the former presence of glaciation in the absence or near-absence of ice-contact indicators; we apply this specifically to the problem of detecting upland glaciation, and consider the implications for Earth’s climate system. Where even piedmont regions are eroded, pro- and periglacial phenomena will constitute the primary record of upland glaciation. Striations on large (pebble and larger) clasts survive only a few km of fluvial transport, but microtextures developed on quartz sand survive longer distances of transport, and record high-stress fractures consistent with glaciation. Proglacial fluvial systems can be difficult to distinguish from non-glacial systems, but a preponderance of facies signaling abundant water and sediment, such as hyperconcentrated flood flows, non-cohesive fine-grained debris flows, and/or large-scale and coarse-grained cross-stratification are consistent with proglacial conditions, especially in combination with evidence for cold temperatures, such as rip-up clasts composed of noncohesive sediment, indicating frozen conditions, and/or evidence for a predominance of physical over chemical weathering. Other indicators of freezing (periglacial) conditions include frozen-ground phenomena such as fossil ice wedges and ice crystals. Voluminous loess deposits and eolian-marine silt/mudstone characterized by silt modes, a significant proportion of primary silicate minerals, and a provenance from non-silt precursors can indicate the operation of glacial grinding, even though such deposits may be far removed from the site(s) of glaciation. Ultimately, in the absence of unambiguous ice-contact indicators, inferences of glaciation must be grounded on an array of observations that together record abundant meltwater, temperatures capable of sustaining glaciation, and glacial weathering (e.g., glacial grinding). If such arguments are viable, they can bolster the accuracy of past climate models, and guide climate modelers in assessing the types of forcings that could enable glaciation at elevation, as well as the extent to which (extensive) upland glaciation might have influenced global climate.

Repulsive segregation of fluoroalkyl side chains turns a cohesive polymer into a mechanically tough, ultrafast self-healable, nonsticky elastomer

Dynamic crosslinking of flexible polymer chains via attractive and reversible interactions is widely employed to obtain autonomously self-healable elastomers. However, this design leads to a trade-off relationship between the strength and self-healing speed of the material, i.e., strong crosslinks provide a mechanically strong elastomer with slow self-healing property. To address this issue, we report an “inversion” concept, in which attractive poly(ethyl acrylate-random-methyl acrylate) chains are dynamically crosslinked via repulsively segregated fluoroalkyl side chains attached along the main chain. The resulting elastomer self-heals rapidly (> 90% within 15 min) via weak but abundant van der Waals interactions among matrix polymers, while the dynamic crosslinking provides high fracture stress (≈2 MPa) and good toughness (≈17 MJ m−3). The elastomer has a nonsticky surface and selectively self-heals only at the damaged faces due to the surface segregation of the fluoroalkyl chains. Moreover, our elastomer strongly adheres to polytetrafluoroethylene plates (≈60 N cm−2) via hot pressing.

Tough antifouling organogels reinforced by the synergistic effect of oleophobic and dipole–dipole interactions

Slippery organogels have gained increasing interest as competitive candidates for antifouling applications. However, it remains challenging to develop tough organogels suitable for fouling resistance in dynamic and flexible application scenarios. Herein, a kind of physically crosslinked organogels with a combination of desirable properties, including high toughness, transparency, surface slipperiness, and fouling resistance is developed. The representative pAL organogels, constructed by poly(acrylonitrile-co-lauryl acrylate) (pAL) copolymer and infiltrated with n-hexadecane as a lubricating solvent, possess high tensile fracture stress, fracture strain, Young’s modulus, and toughness of 4.28 MPa, 517%, 2.52 MPa, and 11.19 MJ m−3. In the organogels, the polar cyano groups from the pAN segments serve as physical cross-linking points, where the synergistic effects played by oleophobic and dipole–dipole interactions significantly toughen the materials. Meanwhile, the soft oleophilic poly(lauryl acrylate) chains offer considerable solvent content, giving rise to satisfactory surface slipperiness. Therefore, the organogels bring about a 57.16% and 81.50% reduction of protein and bacteria adhesion in comparison to the control. The satisfactory antifouling performance has been further confirmed with Spirulina platensis. It is deemed that this organogel may provide great potential for various applications in the future such as anti-adhesion materials and self-cleaning coating.

Fabrication of superhydrophobic and lyophobic paper for self‑cleaning, moisture-proof and antibacterial activity

Paper-based materials have been used in every aspect of social life. However, the current paper-based materials face unprecedented challenges, such as limited lifespan and poor mechanical strength, owing to the deformation after absorbing a large amount of water and bacterial erosion. Herein, superhydrophobic and lyophobic paper was fabricated using internal sizing technology. Hydrophobically modified starch and Ag@SiO2 particles were added as two functional additives to paper pulp to promote a hierarchical structure formation with low surface energy. Consequently, the water and linseed oil contact angles of the obtained paper reached 154.8° and 138.4°, respectively. The resistance to moisture and water vapor also improved under high-humidity condition, the relative moisture content decreased from 511% to 278% and water vapor transmission rate also decreased from 97.44 to 21.23 g/m2·h. Furthermore, its mechanical properties could also be well maintained with a high fracture stress of 4.91 MPa. Besides, some liquid food, such as honey, easily rolled off the surface without leaving behind any residue, which demonstrated its self-cleaning ability. Furthermore, the modified paper exhibited notable bacterial repellency and antibacterial activity. This study provides an innovative method for endowing conventional paper with superhydrophobic and antibacterial properties, which can effectively expand their application scope.

Fabrication and evaluation of biodegradable multi-cross-linked mulch film based on waste gelatin

Microplastics from wasted traditional nondegradable plastic mulching films pose a great threat to both the ecological environment as well as human health. Currently, eco-friendly and cost-effective biodegradable films are considered the most promising substitutes for nondegradable plastic mulching films. In this study, we demonstrate a simple and eco-friendly strategy to utilize the gelatin extracted from scrap skin in leather processing and prepare novel biodegradable mulch films. The gelatin chains were covalently cross-linked with tetrakis(hydroxymethyl)phosphonium chloride to reduce the hygroscopicity of gelatin. Then, polyvinyl alcohol (PVOH) was introduced into the gelatin network. The hydrogen bonds between the gelatin and PVOH and several PVOH crystalline domains acted as sacrificial bonds for energy dissipation. Thus, the multi-cross-linked gelatin matrix (GP) films showed high fracture stress (12.03–31.99 MPa) and fracture strain (211.99%–379.73%). Such high mechanical performance is comparable to that of traditional low-density polyethylene mulch films and conforms to the GB/T 35,795 regulatory standards. In addition to their excellent mechanical properties, the mulch films exhibited good water resistance, excellent light transmittance, and good biodegradability in soil. All properties of the GP films are tunable, and their eco-friendliness, low cost, and excellent properties endow them with great application potential as eco-friendly mulch films for agriculture.

Bones of teleost fish demonstrate high fracture strain

The endoskeleton of teleosts (bony fish) includes a vertebral spine with articulating rib bones (RBs) similar to humans and further encompasses mineralized tissues that are not found in mammals, including intermuscular bones (IBs). RBs form through endochondral ossification and protect the inner organs, and IBs form through intramembranous ossification within the myosepta and play a role in force transmission and propulsion during locomotion. Based on previous findings suggesting that IBs show a much higher ability for fracture strain compared to mammalian bones, this study aims to investigate whether this ability is general to teleost bones or specific to IBs. We analyzed RBs and IBs of 25 North Atlantic Herring fish. RBs were analyzed using micro-mechanical tensile testing and micro-computed tomography, and both RB and IB were additionally analyzed with Raman spectroscopy. Based on our previous results from IB, we found that RBs are more elastically deformable (on average, 50% higher yield strain and 115% higher elastic work) and stronger (55% higher fracture stress) than values reported for IBs. However, these differences were neither associated with a higher Young’s modulus nor a higher degree of mineralization in RBs. Astonishingly, RBs and IBs showed similar fracture strains (12–15% on average, reaching up to 20%), reflecting a much higher ability for tensile deformation than reported for mammalian bone, and further highlighting the biomimetic potential of teleost fish bones for inspiring innovative biomaterials.

Experimental Assessment of Mineral Filler on the Volumetric Properties and Mechanical Performance of HMA Mixtures

This research is conducted to evaluate the influence of mineral filler on the volumetric properties, mechanical and field performance of Hot Mix Asphalt (HMA). Two mineral filler types, namely, Hydrated Lime (HL) and Dust Plant (DPt) were used. Three filler proportions were utilized greater than 1% which represents the most applicable percentage, especially for HL, used by the Ministry of Transportation Ontario (MTO). The effect of filler on various volumetric properties including Voids In Mineral Aggregates (VMA), Voids Filled With Asphalt (VFA), dust to binder ratio (Dp) is examined. Mechanical and predicted field performance of HMA to the best filler proportion that meets all the MTO limitations is also investigated. The obtained results indicated that the Optimum Asphalt Content (OAC), VMA, and VFA decrease as the filler content is increased. HMA mixtures that includes DPt filler had the higher values of VMA, VFA, and OAC compared to the hydrated lime. The addition of filler with 2.5% percentage is very successful for both filler types due to satisfying all MTO requirements for volumetric properties of HMA. Based on MTO specifications, the addition of 2.0% filler seems to be unsuccessful for both filler types due to lowering the Dp ratio. Mix design with 3.0% filler was also unsuccessful because of the lower value of OAC meaning that the mix is dry and there is insufficient asphalt binder to coat the aggregate particles. Besides, filler type has a significant effect on the mechanical properties of the HMA mixtures. As a filler in HMA mixtures, the utilization of HL as a portion of 2.5 % leads to a significant improvement in mixture resistance to water and freezing and thawing. The mixtures that included HL have a higher cracking resistance, greater stiffness, and a higher fracture stress than the mixtures that included DPt. Furthermore, predicted field performance indicated better outcomes for mixes with HL compared to DPt mixes. Doi: 10.28991/cej-2020-03091619 Full Text: PDF

Polyzwitterions as a Versatile Building Block of Tough Hydrogels: From Polyelectrolyte Complex Gels to Double-Network Gels.

The high water content of hydrogels makes them important as synthetic biomaterials, and tuning the mechanical properties of hydrogels to match those of natural tissues without changing chemistry is usually difficult. In this study, we have developed a series of hydrogels with varied stiffness, strength, and toughness based on a combination of poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), a strong acidic polyelectrolyte, and poly-N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium) (PCDME), a polyzwitterion with a weak acidic moiety. We demonstrate that modifying the true molar ratio, R, of PCDME to PAMPS results in four unique categories of hydrogels with different swelling ratios and Young's moduli. When R < 1, a negatively charged polyelectrolyte gel (PE) is formed; when 1 < R < 3, a tough and viscoelastic polyelectrolyte complex gel (PEC) is formed; when 3 < R < 6.5, a conventional, elastic interpenetrating network gel (IPN) is formed; and when R > 6.5, a tough and stiff double-network gel (DN) is formed. Both the PEC and DN gels exhibit high toughness and fracture stress, up to 1.8 and 1.5 MPa, respectively. Importantly, the PEC gels exhibit strong recovery properties along with high toughness, distinguishing them from DN gels. Without requiring a change in chemistry, we can tune the mechanical response of hydrogels over a wide spectrum, making this a useful system of soft and hydrated biomaterials.

Glacial vis-à-vis tectono-provenance signals of the Plio-Pleistocene sediments of the intermontane Kashmir basin, northwestern Himalaya: Evidence from quartz micro-textures and a till deposit

The Himalayan-Tibetan orogen has a great influence on regional and global atmospheric circulation and, hence, it is important for understanding the dynamics of global environmental change. The Kashmir valley, located in the northwestern Himalaya, provides a unique sequence of continuous sedimentary records of unconsolidated sediments of more than a km thickness, dated back to 4 Ma. There are number of studies which suggest episodic and widespread cold conditions, including glaciations, within the Kashmir valley during the Plio-Pleistocene. In order to test the hypothesis of the glacial input into the Kashmir basin, scanning electron microscopy (SEM) was applied to analyze quartz grains of the Karewa deposits stratigraphically for the evidence of their sedimentary history. The microtextures indicate the dominant presence of sustained high stress fractures on the quartz grains with little effect of weathering and dissolution from 4 to 2.1 Ma and from 1.6 to 0.4 Ma. The quartz grains are also angular and of high relief. All these features suggest that these sediments are primarily transported by glaciers and melt water streams. However, the samples ranging in age from 2.1 to 1.7 show a mixed signal (glacial and fluvial) with a dominance of fluvial signal. This transition is attributed to the source area change from the Himalayan range (NE) to the Pir Panjal range (SW) because of the uplift along the Main Boundary Thrust (MBT). Furthermore, we report the first occurrence of a till deposit within the lower part (Dubjan Member 4–3.5 Ma) of the Karewa Group of the Kashmir basin which points to ice advancement in the northwestern Himalaya during the mid-Pliocene. Since, the till occurs in the upper part of the Dubjan Member, therefore, the timing of this glaciation can be restricted to be between 3.7 and 3.5 Ma. Hence, matches well with the mid-Pliocene glaciation that occurred in the Tibetan Plateau (~3.6 Ma) and other parts of the Northern Hemisphere (3.5 Ma).