Tearing Behavior Research Articles

Moisture barriers used in firefighters' protective clothing: Effect of accelerated ultraviolet radiation aging on their mechanical and barrier performance

AbstractFirefighters rely on their protective clothing as a second skin to perform their job. In the middle of this multilayered protective garment, the moisture barrier plays a vital role in preventing liquids to enter while allowing perspiration to escape. This research delves into the impact of accelerated ultraviolet (UV) aging on the performance of firefighter protective clothing moisture barriers, focusing on tear force retention, water vapor transmission rate (WVTR), and wetting via apparent contact angle. Changes in the tearing behavior and reductions in the tear force and tearing distance were observed after aging. Additionally, a reduction in WVTR was found for all the moisture barriers, due to pore closure in the ePTFE/FR PU membrane. In terms of water repellency, the base fabric side of one moisture barrier experienced a transition from hydrophobic to superhydrophilic potentially due to the degradation of the water‐repellent finish. The investigation also revealed that, due to the screening effect by the outer shell fabric, only a low percentage of UV radiation received by the turnout gear, less than 2% in the UVA range, may reach the moisture barrier. These results indicate the need to consider realistic exposure scenarios when assessing moisture barrier service life.

Mode III Tear Resistance of Bombyx mori Silk Cocoons.

This paper concerns the tear properties and behavior of Bombyx mori (B. Mori) silk cocoons. The tear resistance of cocoon layers is found to increase progressively from the innermost layer to the outermost layer. Importantly, the increase in tear strength correlates with increased porosity, which itself affects fiber mobility. We propose a microstructural mechanism for tear failure, which begins with fiber stretching and sliding, leading to fiber piling, and eventuating in fiber fracture. The direction of fracture is then deemed to be a function of the orientation of piled fibers, which is influenced by the presence of junctions where fibers cross at different angles and which may then act as nucleating sites for fiber piling. The interfaces between cocoon wall layers in B. mori cocoon walls account for 38% of the total wall tear strength. When comparing the tear energies and densities of B. mori cocoon walls against other materials, we find that the B. mori cocoon walls exhibit a balanced trade-off between tear resistance and lightweightness.

Modification of the resistive tearing instability with Joule heating by shear flow

We investigate the influence of background shear flow on linear resistive tearing instabilities with Joule heating for two compressible plasma slab configurations: a Harris current sheet and a force-free, shearing magnetic field that varies its direction periodically throughout the slab, possibly resulting in multiple magnetic nullplanes. To do so, we exploit the latest version of the open-source, magnetohydrodynamic spectroscopy tool Legolas. Shear flow is shown to dramatically alter tearing behavior in the presence of multiple magnetic nullplanes, where the modes become propagating due to the flow. Finally, the tearing growth rate is studied as a function of resistivity, showing where it deviates from analytic scaling laws, as well as the Alfvén speed, the plasma-β, and the velocity parameters, revealing surprising nuance in whether the velocity acts stabilizing or destabilizing. We show how both slab setups can produce growth rate regimes, which deviate from analytic scaling laws, such that systematic numerical spectroscopic studies are truly necessary, for a complete understanding of linear tearing behavior in flowing plasmas.

Temperature-Dependent Tearing Behavior of Rubber Materials: Characterization and Modeling

Temperature-Dependent Tearing Behavior of Rubber Materials: Characterization and Modeling

A hot tearing propagation model for steel

Hot tearing is a significant challenge in material preparation process, including high-performance alloy casting, large ingot production and additive manufacturing, etc. However, the propagation process of hot tears, especially in steel, is still unclear at present. This study proposed a new model for hot tearing propagation that considers the energy balance, the relationship between the propagating mode and the growth rate of hot tears when they undergo irreversible and rapid propagation. To evaluate this model, a new testing device was developed and the hot tearing behaviors of low and high carbon steels were observed. The tests demonstrated a notable correlation with the model. Furthermore, a new criterion for propagation of hot tearing was put forward. This work provides a more comprehensive physical model and criteria for simulating and predicting the formation of hot tears.

Effects of Fe, Si, Cu, and TiB2 Grain Refiner Amounts on the Hot Tearing Susceptibility of 5083, 6061, and 7075 Aluminum Ingots

Aluminum alloys 5083, 6061, and 7075 are prone to hot tearing under direct-chill casting conditions; the defects that form during solidification of those alloys are highly sensitive to variation in the alloying elements, with these elements commonly being Si, Fe, Cu, and Ti. This study investigates the influence of the morphology, content, and size of intermetallic compounds on the hot tearing behavior of the 5083, 6061, and 7075 aluminum alloys by combining a constrained rod casting technique, phase diagram calculation, and multiscale microstructural characterizations. The fishbone-shaped α-Al15(Fe,Mn)3Si2 in 5083 can serve as a path for crack nucleation and growth, and an increase in Si content results in Mg2Si assuming fishbone morphology, thereby increasing hot tearing susceptibility. The amount of plate-like β-Al5FeSi is the primary factor controlling the hot tearing susceptibility of 6061. For 7075, increasing the Cu content can greatly enhance the remaining liquid fraction, feeding, and hot tearing susceptibility. For all three alloys, TiB2 grain refiner minimizes hot tearing. This study elucidates the influences of the amounts of Fe, Si, Cu, and TiB2 grain refiner on hot tearing susceptibility. The findings can help establish compositional control standards for the 5083, 6061, and 7075 aluminum alloy series, particularly when the recycling rate must be increased.

Tensile and Tearing Properties of a Geocomposite Mechanically Damaged by Repeated Loading and Abrasion

The behaviour of geosynthetics can be affected by many agents, both in the short and long term. Mechanical damage caused by repeated loading or abrasion are examples of agents that may induce undesirable changes in the properties of geosynthetics. The research conducted in this work complemented previous studies and consisted of submitting a geocomposite, isolated and successively, to two degradation tests: mechanical damage under repeated loading and abrasion. The geocomposite (a nonwoven geotextile reinforced with polyethylene terephthalate filaments) was tested on both sides (with or without filaments) and directions (machine and cross-machine). The impact of the degradation tests on the geocomposite was quantified by monitoring changes in its tensile and tearing behaviour. The results showed that, in most cases, the degradation tests caused the deterioration of the tensile and tearing behaviour of the geocomposite, affecting its reinforcement function. The decline in tensile strength correlated reasonably well with the decline in tearing strength. Changing the side and direction tested influenced, in some cases (those involving abrasion), the degradation experienced by the geocomposite. The reduction factors (referring to tensile and tearing strength) for the combined effect of the degradation agents tended to be lower when determined by using the common method (compared to those resulting directly from the successive exposure to both agents).

Trapezoidal tearing behavior of laminated fabrics used in Firefighters' protective clothing

AbstractLaminated fabrics offer a unique combination of properties and are widely used in various applications, including as moisture barriers in firefighters' protective clothing. Tearing is a common testing method used to evaluate the mechanical performance of laminated fabrics. However, limited information is available on the tearing behavior of laminated fabrics using the trapezoidal procedure. Using high‐speed imaging, this study examined the tearing process of three moisture barriers commonly used in firefighters' protective clothing. The results revealed that the tearing process varied depending on factors such as the structure of the base fabric, the presence of an extra coating on top of the membrane, and the continuous or discontinuous nature of the adhesive layer. This study provides insight into the effect of each component of a laminated fabric on the tearing process, and can inform the design of better performing moisture barriers.Highlights Study of trapezoidal tearing behavior of moisture barriers. Analysis by high‐speed imaging and field emission scanning electron microscope. Influence of base fabric, adhesive configuration, presence of extra coating. Cyclic tearing pattern for woven base fabric and dot adhesive. Continuous tearing for nonwoven base fabric and continuous adhesive.

Revealing hot tear formation dynamics in Al–Cu alloys with X-ray radiography

Hot tears can arise during the late part of alloy solidification because of the shrinkage of isolated liquid as it turns to solid and may have a catastrophic effect on cast tensile properties. Although there are correlations to suggest alloy hot tear sensitivity to casting conditions, they do not capture the influence of microstructure on tearing, such as second-phase particles or intermetallic compounds (IMCs) commonly present in engineering alloys. We use in situ X-ray radiography to quantify the formation and growth behaviour of hot tears in Al-5Cu and Al-5Cu-1Fe alloys during solidification. An automated hot tear detection, tracking and merging algorithm is developed and applied to reveal the role of Fe-rich IMC particles, typical of recycled alloys, on hot tear behaviour. These defects are termed hot tears here on the basis of their complex, extended inter-connected morphology, distinct from more rounded shrinkage porosity. We also visualise and quantify the velocity of interdendritic flow driven by solidification shrinkage, and estimate the pressure changes due to shrinkage. Hot tearing starts at lower solid fraction when IMCs are present due to reduced interdendritic flow, and hot tear formation is more spatially homogeneous, less clustered and more numerous. We show that the largest, most damaging hot tears form from many merging events, that is enhanced by the presence of IMCs.

EVALUATING THE CRACK TIP FORMATION AND PROPAGATION ENERGY OF A TROUSER TEAR SPECIMEN

ABSTRACT An elastomer’s tear behavior is commonly characterized through trouser tear tests. Using a well-understood analytical solution, the force at which the sample tears is used to calculate the elastomer’s tearing energy. By characterizing the tear behavior over a range of rates, a tear profile can then be built that describes the overall fracture resistance of the compound. However, some of the key assumptions that underpin the analytical solution may not be realistic, particularly in cases where the crack propagates in an unsteady manner. Within this article, these deviations are further studied through the use of physical testing and finite element modeling. The work demonstrates a heavy reliance on the sample’s thickness, beyond the levels currently appreciated. Furthermore, the work highlights the presence of a formation zone prior to the point at which the crack propagates uniformly. It is suggested that when evaluating an elastomer’s tear behavior, both the formation zone and propagation zone energies be captured.

A MICROSCOPY INVESTIGATION OF RUBBER COMPOUND CRACK PRECURSORS AND TENSILE FRACTURE SURFACES

ABSTRACT Tensile stress–strain testing is used to investigate the fracture behavior of carbon black–reinforced styrene–butadiene rubber, using 50 replicate specimens. Four vulcanized rubber compounds are studied: a CB-filled SBR with standard mixing conditions (control), the same formulation with intentional poor mixing of the CB, and materials identical to the control material but formed by adding minor amounts of 0.5-mm-diameter glass microspheres (beads)—serving as large model defects/inclusions—using a two-roll mill at two levels, corresponding to average values of 0.78 and 6.24 beads per gauge section region of the tensile test specimen. Microscopy analysis of the resulting fracture surfaces was conducted to complement our recent publication on Weibull failure statistics for distributions of tensile strength and crack precursor size. All 200 fractured specimens from tensile testing at 23°C were imaged with light microscopy and exhibited fracture surfaces characterized by relatively smooth planes perpendicular to the uniaxial loading direction. Most tensile failures originated from the edges of the dumbbell specimens, in line with expectations from fracture mechanics. Light microscopy revealed concentric fracture ring features of high specular reflectance emanating from crack precursors, which are a universal feature of the failure process for these compounds and independent of precursor type, size, or location. Noncontact interferometric microscopy confirmed that the rings resulted from variations in surface micro-roughness, proceeding outward from the precursor as rough–smooth–rough to the edge of the fracture surface. Fracture rings were also observed for tensile tests performed at 80°C. The variation in surface roughness of the fracture surface has parallels to the stick–slip tearing behavior seen for rubbers torn at medium to high rates. To the best of the authors’ knowledge, this is the first time that such striking features have been reported.

Effect of the Slit on the Mechanical Tearing Behavior of High-Density Polyethylene and Polyester Geocell Strips

Geocells are widely applied in numerous infrastructure constructions, like heavy-haul railways and ports. The mechanical tearing behavior of a geocell strip is crucial to the stability of the geocell-reinforced soil structures. At present, extensive studies have been conducted on the tensile characteristics of geocell strips, while limited research has been performed to investigate the post-damage mechanical tearing behavior of geocell strips. Meanwhile, there is also a lack of research on the comparison of performance of strips before and after damage. In this paper, a series of trapezoidal tearing tests were performed on high-density polyethylene (HDPE) and polyester (PET) geocell strips. The tearing test results and failure mode of trapezoidal specimens with a slit were investigated, and the effect of the slit on the strength and deformation characteristics of the specimen were discussed by introducing the “damage ratio of tearing force (RTF)” and “damage ratio of tearing displacement (RTD)”. In addition, the mechanical tearing behavior of HDPE and PET trapezoidal specimens was also compared. The test results indicated that the failure mode of HDPE and PET specimens subjected to tearing force was ductile and brittle failure. The strength and deformation characteristics of post-damage HDPE and PET trapezoidal specimens decreased. The slit had a significant impact on the tearing displacement of HDPE and PET specimens, especially the post-peak tearing displacement. The post-peak tearing displacement of HDPE was 10.99 times that of PET. The peak tearing force of the HDPE specimen without the slit was about 1.61 times that of specimen with the slit. Before local tearing, the peak tearing force of the PET specimen without the slit was about 3.27 times that of the specimen with the slit. The strength damage to the HDPE and PET geocell strips caused by the slit was 38.0%, and 69.46%. The impact of the slit on the tearing force of the PET specimen was greater than that of the HDPE, and was 1.82 times for the HDPE. This study can enhance our understanding of the mechanical tearing behavior of the geocell strip after damage and develop effective mitigation measures.

Investigation of microstructural failure in the human cornea through fracture tests

Fracture toughness of the human cornea is one of the critical parameters in suture-involved corneal surgeries and the development of bioengineered mimetics of the human cornea. The present article systematically studied the fracture characteristics of the human cornea to evaluate its resistance to tear in the opening (Mode-I) and trouser tear mode (Mode-III). Tear experiments reveal the dependency of the fracture behavior on the notch size and its location created in the corneal specimens. The findings indicate lamellar tear and collagen fiber pull-out as a failure mechanism in trouser tear and opening mode tests, respectively. Experimental results have shown a localized variation of tear behavior in trouser tear mode and indicated an increasing resistance to tear from the corneal center to the periphery. This article demonstrated the complications of evaluating fracture toughness in opening mode and showed that the limbus was weaker than the cornea and sclera against tearing. The overall outcomes of the present study help in designing experiments to understand the toughness of the diseased tissues, understanding the effect of the suturing location and donor placement, and creating numerical models to study parameters affecting corneal replacement surgery.

Shedding light on the viscoelastic behavior of artificial and human tears: A microrheological approach

This study conducts research on the viscoelastic properties of biological fluids, including both hyaluronic acid-containing lubricating eye drops and human tears, by means of passive microrheology. By tracking the Brownian motion of tracer particles of various sizes in the fluids, we were able to probe their viscoelastic properties. The results showed that the viscoelastic properties of artificial tears, such as Newtonian viscosity and relaxation time, scale to the concentration and macromolecular size of hyaluronic acid, resembling unentangled semidiluted solutions. Moreover, human tears were found to have a viscosity that is 50% greater than that of pure water, comparable to artificial tears containing 0.1% hyaluronic acid, but with a relaxation time one order of magnitude longer than ophthalmic solutions. This behavior was attributed to their intricate composition. The distinctive aspect of this study lies in demonstrating the feasibility of measuring the rheological properties of human tears, a biofluid of great interest, using extremely small sample volumes and microrheology, providing comprehensive information across a wide range of frequencies approaching those corresponding to blinking upon the application of the Cox–Merz rule. These findings are of significant value as they pave the way for future research on small volumes of tears from ophthalmic patients.

Dynamics of Oceanic Slab Tearing During Transform‐Fault Horizontally‐Oblique Subduction: Insights From 3D Numerical Modeling

AbstractOceanic‐plates vertical tearing is seismically identified in the present‐day Earth. This type of plate tearing is frequently reported in horizontally‐oblique subduction zones where transform‐faulted oceanic plates are subducting (or subducted). However, the mechanisms behind vertical slab tearing are still poorly understood, thus we utilize 3D time‐dependent Stokes' flow thermo‐mechanical numerical models to further study this problem. We find that (a) the age offset of transform fault and (b) the horizontal obliqueness of subduction fundamentally control the tearing behavior of two generic, materially homogeneous oceanic slabs separated by a low‐viscosity zone. The two slabs sequentially bend, which combined with the age‐thickness difference between slabs, causes the differential sinking of them. Based on the modeling results, well‐developed slabs vertical tearing would happen when the oblique angle of subduction is ≥30° or the age ratio of the secondly bent to firstly bent slab being ∼<0.6. Quantifying the horizontal distance‐vector between sinking slabs, we find that subduction at medium‐low horizontal‐obliqueness angles (≤40°) of young lithosphere (slabs‐average ∼15 Myr) tends to produce fault‐perpendicular tearing. Contrastingly, old‐age slabs (average ≥ 30 Myr) with medium‐large obliqueness angles (∼>20°) tend to produce fault‐parallel tearing, related to differential slab‐hinge retreat or rollback. Correlations between slabs' (a) computed tearing horizontal‐width and (b) scaling‐theory forms of their subduction‐velocity differences, are reasonable (0.76–0.97). Our numerically predicted scenarios are reasonably consistent with plate‐tear imaging results from at least four natural subduction zones. Our modeling also suggests that continual along‐trench variation in subduction dip angle may be related to a special case of oblique subduction.

Hot tearing behavior of AZ91D magnesium alloy

Hot tearing is a serious destructive solidification defect of magnesium alloys and other casting metals. Quantitative and controllable measurements on the thermal and the mechanical behavior of an alloy during its solidification process are crucial for the understanding of hot tearing formation. We developed a new experimental method and setup to characterize hot tearing behavior via controlled cooling and active loading to force hot hearing formation on cooling at selected fractions of solid. The experimental setup was fully instrumented so that stress, strain, strain rate, and temperature can be measured in-situ while hot tearing was developing. An AZ91D magnesium alloy, which is prone to hot tearing, was used in this study. Results indicate that when hot hearing occurred, the local temperature, critical stress, and cumulative strain were directly affected by strain rate. Depending on the applied strain rate, hot tearing of the AZ91D magnesium alloy could occur in two solidification stages: one in the dendrite solidification stage (fS ∼ 0.81–0.82) and the other in the eutectic solidification stage (fS ∼ 0.99). AZ91D alloy exhibited distinct mechanical behaviors in these two ranges of fraction solid.

Hot Tearing Behavior of ZL205A Alloy Cylindrical Low-Pressure Castings with Slit Gating and Feeding System

Hot Tearing Behavior of ZL205A Alloy Cylindrical Low-Pressure Castings with Slit Gating and Feeding System

Effect of GNPs and resin blend on tear resistance of 4D printed shape memory photopolymer composite

PurposeThe tear strength (Ts) is a significant property for any kind of soft polymeric material such as rubber, elastomer, viscoelastic material and its composites, to quantify the suitability of a material for any shape memory applications. Many times, the soft elastomeric polymer material has to be capable enough to deform to a maximum extent of displacement but at the same time, it has to withstand the maximum load without fail. Along with shape recovery properties (i.e. the ability to recover its shape from programmed to the original), the success of the shape memory cycle is mainly depending on its stiffness and strength. It has to resist tear during stretching (i.e. programming stage) as repeatedly subjected to deformation, and, hence, it is important to study the tear behaviour for shape memory polymers (SMPs) and their composites. The purpose of the work is to investigate the effect of parameters on Ts of 4D printed specimen using Taguchi method.Design/methodology/approachThe objective of the work is to tailor the Ts of SMPs by reinforcing the graphene nano particles (GNPs) in a blended photopolymer (PP) resin with flexible PP and hard PP resin. In this study, a total of nine experiments were designed based on the L9 orthogonal array (OA) using the design of experiments (DOEs). All the shape memory photopolymer composite’s (SMPPCs) specimens are fabricated using masked stereolithography (MSLA), also known as resin three-dimensional printing (R3DP) technique.FindingsSpecimens are tested using universal testing machine (UTM) for maximum tear force (Fmax) and displacement (δ) caused by tearing the specimen to evaluate the strength against the tear. The results showed that the Wt.% of resin blend highly influenced both Fmax and δ, while GNPs also had an impact on δ. The specimens are offering more tear resistance for those specimens blended with less Wt.% of flexible PP at the same time the specimens enable more δ for those specimens reinforced with 0.3 Wt.% GNPs at 10-s exposure time. The optimum combinations are A1, B1 and C3 for the Fmax and Ts and at the same time A1, B3 and C3 for δ.Research limitations/implicationsTo customise the tear resistance of SMPPCs using MSLA 3 D printing, this study suggested a blend of PP resins reinforced with GNPs. This opens up a new path for creating novel, inexpensive multi-functional 4-dimensional (4D) printed parts.Originality/valueThe use of flexible PP and hard PP resin blends, fabricating the SMPPCs specimens using 3 D printed MSLA technology, investigating the effect of GNPs, resin blend and exposure time, optimizing the process parameters using Taguchi and the work were all validated using confirmation tests and regression analysis using test train method, which increases the originality and novelty.

High-Speed Imaging Analysis of Laminated Fabric Tearing Behaviour

Laminated fabrics are widely used in diverse industries because of their ability to adapt to many different functions. Understanding their tear force behaviour is critical to evaluate their serviceability. The tearing behaviour of laminated fabrics can be examined using high-speed imaging and analyzed using image analysis techniques. This technique is an attractive tool to elucidate the tearing behaviour of laminated fabrics. Through high-speed imaging it is possible to observe the tearing process on the fabric (e.g., yarns bearing the load before failure, yarn breaking behaviour) and membrane (e.g., pop-in crack length, crack propagation, formation of wrinkles, thinning) sides of the laminated fabrics to understand the tearing behaviour. In addition, this technique helps quantify different phenomena such as the membrane pop-in crack length, and crack wake bridging width by yarns. High-speed imaging analysis is a promising technique to visualize the tear phenomena in laminated fabrics.

An integrated approach to study the hot tearing behavior by coupling the microscale phase field model and macroscale casting simulations

Hot tearing is the serious defect that occurs in aluminum alloy castings. A constitutive model of the aluminum alloy mushy zone is vital for the accurate prediction of hot tearing and thermal stress. In this study, an integrated approach was developed to study the hot tearing behavior of cast aluminum alloys. The constitutive behavior and rheological properties of the solidifying aluminum alloys were determined using phase-field simulations and micromechanical calculations. Subsequently, an elastic–viscoplastic (E-VP) constitutive model was constructed for thermal stress analysis and hot tearing prediction. To verify the analysis results, constrained rod casting (CRC) experiments were performed using a permanent mold and a mushy zone deformation and hot tearing propagation mechanism was established based on the casting experiments results. The study indicates that the E-VP model, which is constructed based on the phase-field simulations and micromechanical calculations in this study, enables high-accuracy hot tearing predictions. Furthermore, the E-VP constitutive model is consistent with the deformation mechanism of the solidifying mushy zone. This work accomplished the comprehensive study on aluminum alloy castings ranging from microstructure simulation to hot tearing prediction, which provides a reference and integrated approach for multi-scale analysis in casting processing. • The study on aluminum alloy casting from microstructure simulation to hot tearing prediction was accomplished. • An integrated approach was developed to obtain the rheological properties of the solidifying aluminum alloys. • A mushy zone deformation and hot tearing propagation mechanism was established. • The E-VP model constructed in this paper enables higher accuracy in hot tearing prediction than the E-P model. • The rheological structure is a possible cause for the hot tearing severity decreases with increasing casting temperature.