Tear Toughness Research Articles

Tough, Slippery, and Low-Permeability Multilayer Hydrogels Modified by Anisotropic Fiber Membrane for Soft Tissue Replacement.

Hydrogels with sustained lubrication, high load-bearing capacity, and wear resistance are essential for applications in soft tissue replacements and soft material devices. Traditional tough or lubricious hydrogels fail to balance the lubrication and load-bearing functions. Inspired by the gradient-ordered multilayer structures of natural tissues (such as cartilage and ligaments), a tough, smooth, low-permeability, and low-friction anisotropic layered electrospun fiber membrane-reinforced hydrogel was developed using electrospinning and annealing recrystallization. This hydrogel features a stratified porous network structure of varying sizes with tightly bonded interfaces, achieving an interfacial bonding toughness of 1.6 × 103 J/m2. The anisotropic fiber membranes, mimicking the orderly fiber structures within soft tissues, significantly enhance the mechanical properties of the hydrogel with a fracture strength of 20.95 MPa, a Young's modulus of 29.64 MPa, and a tear toughness of 37.94 kJ/m2 and reduce its permeability coefficient (6.1 × 10-17 m4 N-1 s-1). Meanwhile, the hydrogel demonstrates excellent solid-liquid phase load-bearing characteristics, which can markedly improve the tribological performance. Under a contact load of 4.1 MPa, the anisotropic fiber membrane-reinforced hydrogel achieves a friction coefficient of 0.036, a 219% reduction compared with pure hydrogels. Thus, the superior load-bearing and lubricating properties of this layered hydrogel underscore its potential applications in soft tissue replacements, medical implants, and other biomedical devices.

A nacre-inspired polymheric multilayer film with high efficiency of low-temperature toughening

Polypropylene (PP) films have been widely used in medical, electronics, and construction fields due to their low cost and excellent comprehensive properties. However, the poor low-temperature toughness of PP films restricts its further applications in extreme cold environments. Here, the nacre-inspired 8-, 32-, 128-, and 512-layer PP/SEBS-based films were constructed via our multilayer blown systems. Compared to the conventional blended films, 128-layer films showed significant improvement under the low-temperature conditions, i.e., 160 %, 150 %, and 136 % in impact toughness, tear toughness, and elongation at break, respectively. The high toughening efficiency of the multilayer films is because of the nacre-inspired multilayer structures, which can develop the multi-stage propagation of the damage behavior such as craze and plastic deformation to dissipate much energy when mechanically broken. Since nacre-inspired PP/SEBS-based multilayer films show high efficiency in low-temperature toughening, this work may provide a possible solution to improving the low-temperature mechanical properties of PP films or even other types of polymeric films.

Microstructure, mechanical properties and tear toughness of laser-welded DP980 dual phase steel

In this study, DP980 steel sheets were laser welded with a laser power of 4.5 kW and a welding speed of 4.5 m min−1. The microstructural evolution and mechanical properties of the welded joint and the effect of notch location on tear toughness were evaluated. Results show that the fusion zone (FZ) was composed of lath martensite, the hardness (276 HV) of the heat-affected zone (HAZ) was lower than that of the base metal (305 HV) resulting from martensite tempering. The welded specimens failed at the soft HAZ with a 98.4% joint efficiency during the tensile test, and the ultimate tensile strength of the as-recieved steel and welded joint was 1026 MPa and 1010 MPa, respectively. The tear energy of the FZ and HAZ was lower than DP980 base metal (BM). Thus, it is considered that the fracture toughness of the joint decreased after welding. The crack growth path of the FZ gradually deviated toward the HAZ during tearing due to the asymmetrical plastic zone at the crack tip. Compared with the ductile fracture of the base metal, the significant decrease in the fracture toughness of the welded joint is due to the weak deformation resistance of tempered martensite.

Towards the Development of a Cartilage-like Nanofiber-Hydrogel Composite

ABSTRACTArticular cartilage plays an important role in synovial joint function, but this function is diminished when cartilage tissue breaks down in osteoarthritis. Tissue engineering is a promising approach for replacing failed cartilage, as cartilage is a relatively simple tissue with no blood supply and very few biological cells. To imitate the structure of natural cartilage extracellular matrix material, three components must be included: the hydrated ground substance, the charges that contribute to compressive stiffness via electrostatic repulsion, and the nanofibrous collagen network that resists tensile deformation and failure. Here, the nanofiber network is considered, with examination of its fracture behavior in an as-electrospun state and following a mild chemical crosslinking process. Mode III fracture testing was used to quantify the tear toughness of the fibrous mats, and failure behavior was qualitatively examined with scanning electron microscopy. In ongoing work, this nanofibrous structure will be combined with a charged polyelectrolyte hydrogel gel to create a biomimetic cartilage-like material. By using biomimicry to replicate what is present in native cartilage tissue, a superior material can be designed and fabricated for use in tissue repair and replacement.

Comparison of the hot-stamped boron-alloyed steel and the warm-stamped medium-Mn steel on microstructure and mechanical properties

The application of high strength steels (HSS) for automotive structural parts is an effective way to realize lightweight and enhance safety. Therefore, improvements in mechanical properties of HSS are needed. In the present study, the warm stamping process of the third generation automotive medium-Mn steel was discussed, the characteristics of martensitic transformation were investigated, as well as the microstructure and mechanical properties were analyzed, compared to the popular hot-stamped 22MnB5 steel in the automotive industry. The results are indicated as follows. Firstly, the quenching rate of the medium-Mn steel can be selected in a wide range based on its CCT curves, which is beneficial to the control of forming process. Secondly, the influence of stamping temperature and pressure on the Ms temperature of the medium-Mn steel is not obvious and can be neglected, which is favorable to the even distribution of martensitic microstructure and mechanical properties. Thirdly, the phenomenon of decarbonization is hardly found on the surface of the warm-stamped medium-Mn steel, and the ultra-fine-grained microstructure is found inside the medium-Mn steel after warm stamping. Besides, the warm-stamped medium-Mn steel holds the better comprehensive properties, such as a lower yield ratio, higher total elongation and higher tear toughness than the hot-stamped 22MnB5 steel. Furthermore, an actual warm-stamped B-pillar of medium-Mn steel is stamped and ultra-fine-grained martensitic microstructure is obtained. The mechanical properties are evenly distributed. As a result, this paper proves that the warm-stamped medium-Mn steel part can meet the requirements of lightweight and crash safety, and is promising for the industrial production of automotive structural parts.

Temperature effects on the fracture resistance of scales from Cyprinus carpio

In this investigation the fracture resistance of scales from Cyprinus carpio was evaluated as a function of environmental temperature. Tear specimens were prepared from scales obtained from three characteristic regions (i.e. head, mid-length and tail) of multiple fish. The fracture resistance was characterized in Mode III loading and over temperatures ranging from −150°C to 21°C. Results showed that there was a significant reduction in tear resistance with decreasing temperature and the lowest resistance to fracture was obtained at −150°C. There was a significant difference in the relative tear toughness between scales from the three locations at ambient conditions (21°C), but not below freezing. Scales obtained near the head exhibited the largest resistance to fracture (energy≈150±25kJm−2) overall. The fracture resistance was found to be primarily dependent on the thickness of the external mineralized layer and the number of external elasmodine plies, indicating that both the anatomical position and the corresponding microstructure are important to the mechanical behavior of elasmoid fish scales. These variables may be exploited in the design of bioinspired armors and should be considered in future studies concerning the mechanical behavior of these interesting natural materials.

Improvement of Tear Toughness of ADC12 Aluminum Alloy by Refined Solidification Structure

Improvement of Tear Toughness of ADC12 Aluminum Alloy by Refined Solidification Structure

New Expression Method for Tear Toughness of Cast and Die-cast Aluminum Alloys

New Expression Method for Tear Toughness of Cast and Die-cast Aluminum Alloys

Effect of Cooling Rates during Solidification of Al-5.5%Mg-2.3%Si-0.6%Mn and Al-13%Mg<SUB>2</SUB>Si Pseudo-Binary Alloys on Their Secondary-Particle Morphology and Tear Toughness

Al–5.5%Mg–2.3%Si–0.6%Mn alloy and Al–13%Mg2Si pseudo-binary alloy were cooled at various cooling rates during solidification. Morphological change of secondary particle was examined. Solidified structure of Al–5.5%Mg–2.3%Si–0.6%Mn alloy consisted of primary α–Al dendrites, Al–Mg2Si eutectic structure and Al6Mn particles. The most significant morphological change was from lamella Al–Mg2Si eutectic structure in the permanent mold cast and the die-cast product to refined and globular Mg2Si phase in the high-speed twin-roll cast product. In contrast, no morphological change was observed for Al6Mn particles. In order to investigate the effect of morphological change of Mg2Si phase on tear toughness, tear toughness tests were performed for Al–13%Mg2Si pseudo-binary alloy cast products produced by permanent mold casting and high-speed twin-roll casting. Unit crack propagation energy (UEp) of the high-speed twin-roll cast products was 5 times higher than that of permanent mold cast products. For permanent mold cast specimens, crack propagation occurred along the interface of plate-like Mg2Si/matrix of the eutectic solidified region and in Al-matrix. But fracture surface of high-speed twin-roll cast specimens was covered with fine dimples. Such difference of fracture mode is due to morphological change of Mg2Si phase from plate-like to globular by rapid cooling.

Effect of cooling rates during solidification of Al–5.5%Mg–2.3%Si–0.6%Mn and Al–13%Mg2Si pseudo-binary alloys on their secondary-particle morphology and tear toughness

Al–5.5%Mg–2.3%Si–0.6%Mn alloy and Al–13%Mg2Si pseudo-binary alloy were cooled at various cooling rates during solidification. Morphological change of secondary particle was examined. Solidified structure of Al–5.5%Mg–2.3%Si–0.6%Mn alloy consisted of primary α–Al dendrites, Al–Mg2Si eutectic structure and Al6Mn particles. The most significant morphological change was from lamella Al–Mg2Si eutectic structure in the permanent mold cast and the die-cast product to refined and globular Mg2Si phase in the high-speed twin-roll cast product. In contrast, no morphological change was observed for Al6Mn particles. In order to investigate the effect of morphological change of Mg2Si phase on tear toughness, tear toughness tests were performed for Al–13%Mg2Si pseudo-binary alloy cast products produced by permanent mold casting and high-speed twin-roll casting. Unit crack propagation energy (UEp) of the high-speed twin-roll cast products was 5 times higher than that of permanent mold cast products. For permanent mold cast specimens, crack propagation occurred along the interface of plate-like Mg2Si/matrix of the eutectic solidified region and in Al-matrix. But fracture surface of high-speed twin-roll cast specimens was covered with fine dimples. Such difference of fracture mode is due to morphological change of Mg2Si phase from plate-like to globular by rapid cooling.

Effects of High-Temperature Solutionizing on Microstructure and Tear Toughness of A356 Cast Aluminum Alloy

A356 alloy was cast into permanent molds and subjected to T6 heat treatment. Two solutionizing (solution heat treatment) temperatures (540°C and 560°C) were used, with the holding time for each varied between 0 min and 240 min. Tear test specimens of 4 mm in thickness were machined from the castings. Tear toughness (UEp: unit crack propagation energy) was obtained from load-displacement curves. With increasing solutionizing holding time, eutectic silicon particles were found to become larger and mean interparticle distance was found to increase. The UEp of specimens solutionized at the higher temperature (560°C) increased with holding time until 120 min but decreased with longer holding times. SEM observation of fracture surfaces after tear testing revealed dimples originating from dispersed silicon particles within the eutectic phase. Fine dimples were also observed in the eutectic aluminum region in specimens with reduced UEp. These fine dimples were different from the dimples found to originate from the eutectic silicon particles.

Effects of high-temperature solutionizing on microstructure and tear toughness of A356 cast aluminum alloy

Effects of high-temperature solutionizing on microstructure and tear toughness of A356 cast aluminum alloy

Influence of processing on the properties of the aluminium alloy 2025 with a zirconium addition

The influence of hot deformation and alloy composition on the tensile properties, tear toughness and exfoliation corrosion susceptibility of aluminium alloy 2025 forgings has been investigated. Two casts of 2025 were used to make extrusion billets. These were of standard composition within the 2025 specification, and a composition outside the permitted range but reflecting more modern alloy design with a 0.12 wt.% addition of zirconium. Billets were hot extruded and hot forged at a range of temperatures expected to produce unrecrystallised, partially and fully recrystallised microstructures. The main objective of the compositional variation was to alter the wrought grain refining intermetallic phase, allowing more control of the grain size produced by heat treatment. After the application of a standard heat treatment, tensile and tear toughness properties were determined. Exfoliation tests were performed in accordance with ASTM-G34. The exfoliation susceptibility and mechanical properties of 2025 forgings have been found to exhibit a dependence on microstructure developed during hot forming and heat treatment but the Zr addition was ineffective in producing a refined microstructure.

Effect of laser beam welding on tear toughness of a 1420 aluminum alloy thin sheet

A tear test has been conducted for a 1420 Al–Li alloy thin sheet and its laser welded joint. The test was based on the ASTM B 871-01, standard test method for tear testing of aluminum alloy products. Moreover, the hardness distribution and microstructure of the alloy and welded joints were investigated. The test results indicate that there exists slight orientation dependence of tear energies for the L–T and T–L base metal. In addition initiation energies are higher than the propagation energies for all the tear test specimens, and the tear energies of base metal are higher than those of weld metal and HAZ. Thus, it is considered that the tear toughness of the laser-welded joints is obviously decreased for the 1420 Al–Li alloy thin sheet. Fracture surface shows strong delamination structure for the base metal. Moreover, there exists a feature of fracture along grains or subgrains for the weld metal. Thus, the obvious decrease in tear toughness of weld metal is due to the transition of fracture mode from transgranular to intergranular.

Tear Toughness Evaluation of High-Quality Squeeze-Cast and Rheocast Aluminium Alloy Castings

Cast plates of A356 aluminum alloy with different thickness were fabricated by rheocasting and squeeze casting. Tear tests were performed on the as-cast and heat-treated products (T5 and T6), and effects of solidified structure and heat treatment on unit crack propagation energy (UEp) were examined. Increased cooling rate (corresponding to a decrease in plate thickness) resulted in refined solidified structure and enlarged UEp values for as-cast samples. For both rheocast and squeeze-cast samples, both spheroidized eutectic Si particles and age-hardened α-Al matrix by T6 treatment were effective for increasing UEp. UEp of the squeeze-cast sample was higher than that of the rheocast sample. Observation of crack growth path and fracture surface revealed that the tear toughness of the present cast alloy was controlled by distribution of eutectic solidified region in the cast structure, which provided a preferential crack growth path. The discontinuous distribution for the squeeze-cast sample is considered to be beneficial for increasing crack growth resistance rather than the continuous arrangement of the network-like eutectic region for the rheocast sample. Relatively small UEp was obtained for the T6 treated rheocast sample collected from the 6 mm thickness plate. This is attributable to the volume fraction of the eutectic solidified region in the sample being larger than others under the present experimental conditions.

ＡＣ４ＣＨアルミニウム合金レオキャスト材およびスクイズキャスト材の引裂靭性

Cast plates of the AC4CH aluminum alloy with different thickness were fabricated by rheocasting and squeeze casting. Tear tests were performed for the as cast and heat treated products (T5 and T6) and effects of solidified structure and heat treatment on the unit crack propagation energy (UEp) were examined. Increase of the cooling rate (corresponding to the decrease in plate thickness) resulted in refined solidified structure and enlarged UEp values for as cast samples. Both spheroidized eutectic Si particles and age-hardened α-Al matrix by T6 treatment were effective to increase UEp for both rheocast and squeeze cast samples. UEp of the squeeze cast was larger than that of the rheocast. Observation of crack growth path and fracture surface revealed that the tear toughness of the present cast alloy was controlled by distribution of eutectic solidified region in the cast structure, which provided a preferential crack growth path. The discontinuous distribution for the squeeze cast is considered to be beneficial for increase in crack growth resistance rather than the continuous arrangement of the network-like eutectic region for the rheocast. Relatively small UEp was obtained for the T6 treated rheocast sample collected from the 6 mm thickness plate. This was caused by the fact that the volume fraction of the eutectic solidified region in the sample was larger than others under the present experimental condition.

摩擦撹はん接合した６Ｎ０１アルミニウム合金継手の引裂靭性評価

Tear toughness tests were performed for a 6 mm thick 6N01-T5 aluminum alloy plate joint by friction stir welding. Tear test specimens were collected in various ways so that the crack propagates through the selected local region of the weld, and by which, the relationship between the crack growth resistance and the local microstructure was examined. Morphology of the load-displacement curve and the obtained unit crack propagation energy (UEp) were systematically changed reflecting the local microstructural difference in the vicinity of the weld region. As for the as-weld condition, UEp of the weld region was larger than that of the T5 treated parent plate. For the middle of the weld region consisting of refined equiaxed grain structure (so called “stir zone”), UEp was larger than the surrounding outer region with a pancake-like grain structure. Specimen surface observation found that fine slip lines appeared when the crack propagated through the stir zone. In contrast, a rough and coarse slip pattern was dominant when the crack propagated through the outer region of the weld zone. The obtained load-displacement curve, UEp values and change in specimen surface appearance provided a quite reasonable correlation to the local microstructual characteristics in the weld zone.

真空ダイカストならびに高速双ロールキャストしたアルミニウム合金の組織と引裂靭性

Vacuum die-cast and high-speed twin-roll cast products were fabricated using a heat-treatable Al-Si-Mg base alloy (A) and a non-heat-treatable Al-Mg base alloy (B). These alloys have almost equivalent tensile strength and ductility but different solidified structure. Tear toughness tests were performed using a small-size specimen and the unit crack propagation energy, UEp, was obtained from the load-displacement curve. For the vacuum die-cast products, both A and B exhibited macroscopically plane fracture surface. Dimple formation nucleated at the globular eutectic Si particles was detected in A. In contrast to that, the fracture surface of B was covered with a lamella eutectic structure. UEp was larger in A than B. Large increase in UEp was obtained for the twin-roll cast products. Their UEp values were 1.8 and 3 times larger than those of vacuum die-cast A and B, respectively. Macroscopic appearance of the twin-roll cast products was characterized by the slanted shear-type fracture path for both A and B. In addition to that, fracture surface of B showed fine dimple fracture surface. Large increase in UEp for B is due to the morphological change of the eutectic structure from the lamellar-type to the fine and globular-type induced by the rapid cooling rate of the high-speed twin-roll casting.

Tear Toughness of Permanent Mold Cast and DC Cast A356 Aluminum Alloys

Cast products of A356 with different microstructural features were prepared; permanent-mold cast (PM) and direct-chill cast (DC) products. For each casting, a sharp notched plate specimen was subjected to static tensile loading until a crack initiated at the notch root and propagated across the width of the specimen. Both maximum load and energy to fracture (the integrated area under the load-displacement curve) increased with decreasing dendrite arm spacing (DAS). The curve of DC was smooth and the energy to fracture was quite large. The load-displacement curve was divided into two segments by a vertical line through the maximum load. The area under the first segment is a measure of the energy necessary to initiate the crack. The second segment represents the energy necessary for crack propagation. Unit energy was computed by dividing the measured energy by the net area of the specimen. Refinement of DAS and grain size increased unit energies for crack initiation (UEi) and propagation (UEp). Comparison among PM products revealed that DAS refinement was effective for increasing UEi. Among the present castings, the DC product with the finest DAS exhibited a significant increase in UEp. Observation of the crack propagation path revealed that the fracture surface was normal to the loading direction for PM. In contrast, for DC, a slanted crack path was dominant through the specimen ligament. The features of the crack propagation path are considered to have affected quantitative balance between UEi and UEp. The increased UEp in DC is considered to be due to the introduced slanted crack. Tear tests were confirmed to provide useful information concerning the effect of solidification structure on toughness, which can serve as a guide for further toughening of aluminum alloy castings.

Tear Toughness Evaluation of a Permanent Mold Cast A356 Aluminum Alloy Using a Small-size Specimen

Tear toughness evaluation of a permanent mold cast A356 aluminum alloy was carried out by using two kinds of specimen with different size. One was equivalent to the specimen size designated in ASTM B871. The other one was about 30% as large as that of standard one in volume. Unit energies for tear fracture were obtained from load-displacement curves, and their specimen size, thickness and microstructure dependency were examined. Unit crack initiation energy (UEi) increased with increase in specimen thickness. Meanwhile, unit crack propagation energy (UEp) monotonically decreased in accordance with increase in specimen thickness. In order to make sure if the UEp values reflected the characteristics of local microstructure difference, the small-size tear specimens were collected from various parts in a single cast product. Larger UEp was obtained in the specimen with finer dendrite arm spacing (DAS). These findings suggest that the tear test using a small-size specimen is useful for toughness evaluation of cast aluminum alloys.