Tear Test Research Articles

Discussion: A Comment on “The Trousers Fracture Test for Viscoelastic Elastomers” (Shrimali, B., and Lopez-Pamies, O., 2023, ASME J. Appl. Mech., 90(7), p. 071010)

Abstract The Rivlin–Thomas classical energy balance model for tearing tests suggests that the fracture energy Γ is proportional to the work of the external load in the legs (potential energy), for not too large stretches in the legs, so the increase of Γ with loading rate is observed or measured, but not really explained by the model. Shrimali and Lopez-Pamies (SLP) have recently built a theory on viscoelastic fracture from recent experimental evidence of a critical (stretch rate-independent) stretch on nucleation of cracks in the pure shear tests. The theory in other words incorporates this evidence in an otherwise energy-based criterion. In the paper “The trousers fracture test for viscoelastic elastomers” (ASME J. Appl. Mech., 2023, 90(7), p. 071010), they seem to obtain the critical (stretch rate-independent) stretch condition for the case of trouser tests (applying their theory from a long enough crack) both in nucleation and steady-state propagation. This outcome seems reasonable since for a linear material, looking at the elastic limit cases of very slow and very fast rates, it would produce an increase of the load, and hence of the fracture energy, proportional to the increase of the modulus, which is in line with what has been found experimentally, although possibly in contrast with classical rate-independent cohesive models, at least for crack nucleation.

Insight into the fracture energy dissipation mechanism in elastomer composites via sacrificial bonds and fillers.

Most tough elastomer composites are reinforced by introducing sacrificial structures and fillers. Understanding the contribution of fillers and sacrificial bonds in elastomer composites to the energy dissipation is critical for the design of high-toughness materials. However, the energy dissipation mechanism in elastomer composites remains elusive. In this study, using a tearing test and time-temperature superposition, we investigate the effect of fillers and sacrificial bonds on the energy dissipation of elastomer composites consisting of poly(lipoic acid)/silver-coated Al fillers. We found that the fillers and sacrificial bonds mutually enhance both the intrinsic fracture energy and the bulk energy dissipation, and moreover the sacrificial bonds play a more important role in enhancing fracture toughness than the fillers. It is unreasonable to rely solely on the loss factor for bulk energy dissipation. The addition of sacrificial bonds results in a chain segment experiencing greater binding force compared to the addition of fillers. This suggests that the chain segment consumes more energy during its movement. By calculating the length of the Kuhn chain segment and the Kuhn number, it is evident that the addition of sacrificial bonds results in a greater binding force for the chain segment than the addition of fillers, and this enhanced binding force increases the energy consumption during the motion of the chain segment.

The Effect of Vidian Neurectomy on the Ocular Surface - The Primary Results from a Six-Month Pilot Study.

To evaluate the effect of vidian neurectomy (VN) on the ocular surface and the possibility of dry eye in the treatment of allergic rhinitis. Twelve participants were recruited in this prospective study. Prior to and after 1 and 6 months of VN, an ocular surface disease index (OSDI) questionnaire was obtained, and the Schirmer's tear test (STT), break-up time (BUT), corneal fluorescence staining (CFS) score, and Keratograph 5M were used to evaluate the ocular surface condition. Two patients (16.67%) met the dry eye diagnosis criteria one month after surgery; however, their symptoms were relieved after to 3-4 months and none of them met the diagnostic criteria for dry eye after six months. Compared with the baseline values, the STT was significantly reduced (P=0.002), while the tear meniscus height (TMH) (P=0.262), break-up time (BUT) (P=0.916), first keratographic tear film break-up time (NK-BUTfirst) (P=0.791), and average keratographic break-up time (NK-BUTave) (P=0.970) did not change significantly 6 months after surgery. The degree of STT decreased from baseline to 6-month and was related to the basic STT (ρ= 0.837, P=0.001) and sex (ρ= -0.584, P= 0.026) but not to age, OSDI score, BUT, NK-BUTfirst, NK-BUTave or CFS (all P>0.05). Among these factors, STT at baseline was confirmed to be a predictor of a decline in tear secretion after surgery (B = 0.731, P<0.001). In this 6-month prospective pilot study, decreased tearing was observed after VN, but this decrease did not increase the possibility of dry eyes.

Comprehensive study of the off-axis mechanical behaviors of a Polytetrafluoroethylene‐ coated fabric after 23 Years of service at Shanghai stadium

Coated fabrics can experience mechanical performance degradation due to environmental factors and long-term stress during service. Hence, studying the mechanical behaviors of these materials after aging is crucial. While PTFE (polytetrafluoroethylene)-coated fabrics are more commonly used than PVC (polyvinyl chloride)-coated fabrics, limited research exists on their performance after aging in practical engineering applications. PTFE-coated fabrics are primarily used in large-span fabric structures, where their mechanical performance under tensile-shear stress is crucial. This study aims to investigate the mechanical behaviors of PTFE-coated fabrics after practical aging under tension-shear stress. Test materials included decommissioned Saint-Gobain Sheerfill-II PTFE-coated fabrics, which had served for 23 years at Shanghai Stadium, and identical new fabrics. Monotonic tensile, central tearing, and cyclic tensile tests were conducted at seven different off-axis angles to compare the mechanical properties of aged fabrics with new fabrics, including tensile strength, tearing strength, modulus of elasticity, and ratcheting strain. Additionally, this study explored changes in failure mechanisms, tearing mechanisms, applicability of strength criteria, and suitability of the orthotropic model after aging. This provides a comprehensive understanding of the mechanical behaviors of aged PTFE-coated fabrics and valuable insights for engineering design.

Comparative evaluation of the intravenous effect of medetomidine, tramadol and medetomidine/tramadol combination on tear production in clinically healthy donkeys (Equus asinus)

Various ophthalmic disorders (conjunctivitis, corneal wounds, keratitis) have been reported in donkeys. There are no studies on the effect of medetomidine or tramadol on Schirmer tear test (STT) readings in donkeys. This prospective study investigated changes in STT readings in 24 clinically healthy donkeys (Equus asinus) (14 geldings and 10 mares) treated with commonly used doses of medetomidine hydrochloride and tramadol hydrochloride as mono- or combined therapy. Analgesia, sedation, ataxia, and STT readings were measured before treatment (baseline) and at different periods after administration (5–120 min) of the specific drug in each group. Tramadol monotherapy induced a mild analgesic effect (score 1) at 10 min post-administration. All treated donkeys exhibited mild to moderate ataxia. Medetomidine alone or in combination with tramadol induced a significant decrease (P&lt;0.05) in the STT readings in both right and left eyes at 5, 15, 30, and 60 min relative to baseline, and the lowest values were observed 60 min after drug administration in both groups. Intravenous administration of medetomidine alone or in combination with tramadol induced a significant reduction in STT readings in clinically healthy donkeys. Therefore, in donkeys, the ocular surface treated with these sedatives should be carefully examined and adequately covered by an artificial tear solution or ophthalmic gel.

Determination of intraocular pressure and Schirmer tear test and the comparison between the applanation tonometer (Tono-Pen AVIA®) and the rebound tonometer (TonoVet Plus®) in mini lionhead rabbits.

To determine intraocular pressure (IOP) and tear production, as well as to compare the IOP obtained with the TonoVet Plus® (rebound) with the Tono-Pen Avia® (applanation) tonometers. Twenty-five Mini Lionhead rabbits (n = 50 eyes). Tear production was measured at 6:00 a.m. and 6:00 p.m. by using the STT. The IOP reading was performed with the rebound tonometer, followed by the applanation tonometer, at 6:00 a.m., 9:00 a.m., 12:00 p.m., 3:00 p.m., and 6:00 p.m. Regression analysis, analysis of variance (anova) and Bland-Altman statistics were used. Daily tear production was 10.25 ± 3.75 mm/min, with no differences among the moments evaluated. Average daily IOP was 17.7 ± 3.08 mmHg with the TonoVet Plus® and 11.5 ± 4.56 mmHg with the Tono-Pen Avia®. IOP values were higher at the beginning and end of the day with both tonometers. The IOP values are higher with the TonoVet Plus® tonometer. The reference values of IOP and tear production obtained in this work may support the diagnosis, treatment, and monitoring of ocular disorders in pet Mini Lionhead rabbits.

Avaliação da porção aquosa da lágrima em Shih-Tzu: comparação do teste lacrimal de Schirmer 1 com a altura do menisco lacrimal

ABSTRACT The aqueous portion of the tear film has been characterized as an essential structure for ocular surface health. Among various assessment tests, some measure the aqueous portion, such as Schirmer Tear Test 1, Meniscometry using a strip, and the test to determine Tear Meniscus Height (TMH). Conversely, few studies have specifically evaluated tear meniscus height, especially those utilizing ocular surface analyzers. Therefore, the aim of this study was to comparatively evaluate the results obtained from employing Tear Meniscus Height (TMH) using an Ocular Surface Analyzer and Schirmer Tear Test 1 (STT-1) in Shih Tzu dogs. To achieve this, the eyes of 18 brachycephalic Shih Tzu dogs of both sexes and varying ages were assessed and compared. The results revealed that the TMH for the right eye was 0.59±0.29mm, and for the left eye was 0.88±0.27mm; p=0.0135. For STT-1, it was found that the right eye had a value of 19.06±4.87mm/min, and the left eye had a value of 23.11±4.80mm/min; p=0.0238. Furthermore, the Pearson correlation test applied between TMH and STT-1 yielded the following results for the right eye (r=0.601; p=0.008) and the left eye (r=-0.032; p=0.8979). The TMH shows potential as an alternative to STT-1 for evaluating the aqueous component of tear film in a similar manner. However, further research is warranted, particularly for establishing reference values for TMH and conducting a comprehensive comparison between STT-1 and TMH. This research is especially important for gathering information that can contribute to the understanding of ophthalmic and systemic conditions that directly influence the physiological composition of tears. Critical for establishing the values obtained when measuring the canine lacrimal meniscus using different techniques is the consideration of associated functional factors.

Performance prediction of polyvinylidene fluoride membrane materials after natural and artificially accelerated aging

This study investigates the performance degradation and prediction of polyvinylidene fluoride (PVDF) membrane materials under natural aging conditions (2 MPa prestress) and artificially accelerated aging conditions. Initially, the tensile strength, elongation at break, elastic modulus, tear strength, and apparent properties (transmittance, reflectivity, and conjugated double bond absorption area) of the membrane material were measured through uniaxial tensile testing, trapezoidal tear testing, and ultraviolet (UV) testing. These measurement results were then compared and analyzed in relation to tear strength and apparent properties under artificially accelerated aging conditions. The results indicate that UV irradiation and 2 MPa prestress play a crucial role in the degradation of PVDF membrane material properties. Finally, an enhanced Arrhenius equation, accounting for the triple effects of irradiation, oxygen pressure, and temperature, and Schwarzschild’s law, were employed to establish a correlation between natural (2 MPa prestress) and artificially accelerated aging performance of PVDF. The results demonstrate that the enhanced Arrhenius equation provides a more accurate prediction compared to Schwarzschild’s law.

A Comparison of the Intrarectal and Intramuscular Effects of a Dexmedetomidine, Ketamine and Midazolam Mixture on Tear Production in Cats: A Randomized Controlled Trial.

Cats are often easily stressed and uncooperative. The use of sedative agents in the feline species is widely used to perform even minor clinical and diagnostic procedures. The aim of this study is to assess the impact on tear film production of the intrarectal route (IR) administration of a mixture of dexmedetomidine, ketamine and midazolam in comparison with the intramuscular (IM) one. A group of twenty cats were involved in a randomized and blinded clinical trial. A clinical and ophthalmological examination was conducted on the cats. The IR group received dexmedetomidine 0.003 mg kg-1, ketamine 4 mg kg-1 and midazolam 0.4 mg kg-1; the IM group received dexmedetomidine 0.003 mg kg-1, ketamine 2 mg kg-1 and midazolam 0.2 mg kg-1. A Shirmer tear test I (STT- I) was conducted 1 h before sedation and 2', 10', 20', 30', 40', and 80' post drug administration. The reaction to STT-I administration was also evaluated. The IM group has a lower mean tear production than the IR group for all time points evaluated. Cats in the IM group showed less reaction to STT-I administration. This study may suggest that the effect of sedative agents administered by the IR route has a lower incidence on tear production than the IM one. The use of eye lubricant is recommended in any case.

SDE

Early screening for dry eye disease (DED) is crucial to identify and provide timely intervention to high-risk susceptible populations. Currently, clinical methods for diagnosing DED include the tear break-up time test, meibomian gland analysis, tear osmolarity test, and tear river height test, which require in-hospital detection. Unfortunately, there is no convenient way to screen for DED yet. In this paper, we propose SDE, a contactless, convenient, and ubiquitous DED screening system based on RF signals. To extract biomarkers for early screening of DED from RF signals, we construct frame chirps variance and extract fine-grained spontaneous blinking action. SDE is carefully designed to remove interference in RF signals and refine the characterization of biomarkers that denote the symptoms of DED. To endow SDE with the ability to adapt to new users, we develop a deep learning-based model of unsupervised domain adaptation to remove the influence of different users and environments in local and global two-level feature spaces. We conduct extensive experiments to evaluate SDE with 54 volunteers in 4 scenes. The experimental results confirm that SDE can accurately screen for DED in a new user in real environments such as eye examination rooms, clinics, offices, and homes.

Progressive retinal atrophy in Turkish Shepherd Dog; A case report

Progressive retinal atrophy (PRA) is described as an inherited degenerative disease of the retina that is common in dogs. The case was a 9-year-old female Turkish shepherd dog. It was presented to the Small Animal Hospital with complaints of polyuria and stranguria. After examination, the diagnosis was acute hepatitis. Medical treatment (ursofalk, milk thistle, prednisolone and N acetyl cystein) was given. The case lost vision after three days of treatment. The ophthalmological examinations were performed as included slit lamp, Schirmer's tear test, applanation tonometry, fluorescein staining and ultrasound. Ophthalmoscopic and fundoscopic examinations revealed hyperreflectivity and colour change in the tapetal region, marked attenuation of retinal vessels, depigmentation in the non-tapetal region, and optic disc atrophy with scalloped borders. Fundoscopic examination revealed retinal degeneration in both eyes. The aim of this case report is to diagnose PRA in Turkish shepherd dogs, to highlight its significance and to share the results with clinicians.

Efficacy of the topical antihistamine olopatadine in dogs with experimentally induced allergic conjunctivitis

AbstractObjectiveThe objective of the study was to evaluate the efficacy of a once a day, over the counter antihistamine eye drop, 0.7% olopatadine hydrochloride, in treating or preventing experimentally induced allergic conjunctivitis in dogs.Animals studiedTwelve systemically healthy pet dogs with no known history of allergies or atopic dermatitis, and in the past 12 months had no known ocular abnormalities.ProceduresDogs were randomly assigned to two groups: “Treatment” which received topical 0.7% olopatadine hydrochloride and “Control” which received artificial tears. Dogs received the antihistamine eye drops before (Phase 1) or after (Phase 2) receiving a compounded ophthalmic histamine solution to induce clinical signs of allergic conjunctivitis. Conjunctival hyperemia, chemosis, follicles, ocular discharge, and ocular pruritus were graded, and photographs were used to document changes. Schirmer tear test values, fluorescein staining, and intraocular pressures were monitored throughout.ResultsIn both Phase 1 and Phase 2, conjunctival scores increased 10 min after histamine administration (p &lt; .05). There was no difference between maximum overall conjunctival scores between treatment and control groups in either phase or when comparing treatment groups of Phase 1 to Phase 2 (p &gt; .05). However, treatment groups in Phase 2 did have a higher maximum conjunctival chemosis score and spent more time at their maximum chemosis score when compared to Phase 1 (p &lt; .05).ConclusionOlopatadine may be beneficial as prophylaxis to reduce the degree and duration of clinical signs of allergic conjunctivitis.

Long-term effect of oral cannabidiol administration to healthy adult dogs on tear production, intraocular pressure, and tear concentrations.

To determine the chronic effects of oral cannabidiol (CBD) use on tear production, intraocular pressure (IOP), and concentration of CBD in tears of healthy dogs. Eighteen healthy research Beagles. This was a masked, placebo-controlled, randomized prospective study. Eighteen dogs were randomly assigned to three groups (six dogs per group) based on daily dosage of oral MCT oil (placebo), CBD 5 mg/kg, and CBD 10 mg/kg. Schirmer tear test (STT-1) and IOP were measured twice daily (7 am and 7 pm) every 4 weeks for 36 weeks. Week 36 tears were collected and analyzed for CBD concentrations (ng/mL) using liquid chromatography/mass spectrometry. A mixed linear model was used as the statistical method and p-value <.05 was considered significant. No significant differences were found between placebo vs. 5 mg/kg vs. 10 mg/kg for STT-1 or IOP (AM and PM). CBD was detected in 10 out of 11 (91%) viable tear samples receiving 5 mg/kg or 10 mg/kg dosages. One sample in the 5 mg/kg group had inadequate tear volume for analysis. The CBD concentration in tears was at or below the lower limit of quantification in placebo group, 4.12-11.2 ng/mL for the 5 mg/kg group, and 6.22-152 ng/mL for the 10 mg/kg group. Long-term administration of oral CBD in healthy research beagles demonstrates a favorable safety profile regarding ocular tolerability. Oral CBD administration does not appear to affect tear production or IOP over a 36-week period. This is the first canine study positively identifying concentrations of CBD in tears following oral administration.

Determination of reference values for tear production and intraocular pressure in Pygoscelis penguins of the Antarctic Peninsula

BackgroundAccording to the literature review, this is the first study investigating tear production (TP) and intraocular pressure (IOP) in the Pygoscelis penguins living in their natural habitat. The study aimed to establish normal values for standard ocular tests in the genus Pygoscelis, namely, the Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins, in four different islands of Antarctica. Sampling was made by specifically using the left eye of the penguins. The Schirmer's tear test type I (STT-I) and the Tonovet® (rebound tonometer) were used to measure the TP and the IOP, respectively.ResultsThe mean TP and IOP values of 129 Adélie, chinstrap, gentoo, and 120 adult Adélie, gentoo penguins were determined as 10.2 ± 4.0 mm/min and 38.9 ± 13.2 mmHg, respectively. No statistical difference was detected between the penguin species for the mean IOP values, while the difference was determined in all the locations. However, statistical differences in the mean TP values were determined between all locations.ConclusionThe results of this study provide a reference range of Schirmer's tear test (STT) and IOP values in Pygoscelis penguins and show that the IOP is significantly affected by locations. This result can be attributed to the harsh climatic conditions of the Antarctic Peninsula that change very quickly. The described data may help diagnose clinical pathological findings in Pygoscelis penguins.The STT and rebound tonometry appears to be safe and reproducible methods in Pygoscelis penguins, as the results were obtained quickly and were well tolerated by the birds.Based on our results, we propose that similar studies can be initiated in crowded colonies of three penguin species of this genus on the Antarctic Peninsula, the southern Shetland Islands, and other frequently visited islands in Antarctica.

К ВОПРОСУ ИСПЫТАНИЯ ПРЕДЕЛА ПРОЧНОСТИ СОЕДИНЕНИЯ СЛОЕВ В БИМЕТАЛЛЕ, ПОЛУЧЕННОМ СВАРКОЙ ВЗРЫВОМ

Studies have been carried out on the types of samples manufactured according to various standards used to test the strength of the «steel + titanium» bimetal. Designs of samples have been determined, tests of which show a more objective assessment of strength. It is proposed to carry out only tear strength testing of the cladding layer to assess the strength of the connection in the bimetal by explosion welding.

Diminished pupillary light reflexes, elevated third eyelids, and decreased tear production are commonly associated with canine dysautonomia.

To retrospectively describe ocular abnormalities reported in dogs with presumed dysautonomia. 79 dogs with dysautonomia. Medical records from the Kansas State University Veterinary Health Center from 2004 to 2021 were reviewed for dogs with a clinical or histopathologic diagnosis of canine dysautonomia (CD). Ophthalmic exam abnormalities, nonocular clinical signs, and outcomes were recorded. Most dogs (73/79 [92.4%]) with CD exhibited at least 1 ocular abnormality. The most common ocular abnormalities were diminished pupillary light reflexes (PLRs) in 55 of 79 (69.6%) dogs and elevation of the third eyelids in 51 of 79 (64.6%) dogs. Schirmer tear test values were bilaterally decreased in 32 of 56 (57.1%) dogs. Other ocular abnormalities included resting mydriasis, ocular discharge, photophobia, blepharospasm, corneal ulceration, and conjunctival vessel pallor. The most common nonocular clinical signs were vomiting or regurgitation in 69 of 79 (87.3%) and diarrhea in 34 of 79 (43.0%) dogs. Pharmacologic testing with dilute 0.01%, 0.05%, or 0.1% pilocarpine yielded pupillary constriction in 42 of 51 (82.4%) dogs. Thirty-two of 79 (40.5%) dogs survived to discharge. Resolution of ocular abnormalities was variable. Ophthalmic abnormalities such as diminished PLRs, elevation of the third eyelids, and decreased tear production are commonly associated with CD and provide support for its antemortem clinical diagnosis, though dogs with normal PLRs can be diagnosed with the disease. Pharmacologic testing with dilute topical pilocarpine in dogs with clinical signs suggestive of dysautonomia supports a diagnosis of CD. Ophthalmic abnormalities may improve or resolve over time.

Cohesive zone modelling to predict crack growth under fatigue loading

This manuscript presents the partial results in the development of numerical models based on Cohesive Zone Modelling to analyse quasi-static and fatigue crack propagation in adhesive interfaces. This work applied to adhesive interface between fibre laminates and structural epoxy adhesive of a wind turbine blade 3rd shear-web connection to the trailing edge panels. Fracture characterization experiments using the Double Cantilever Beam with Unequal Bending Moments (DCB-UBM) specimen are performed, and results are used to determine different modelling parameters, such as the mixed-mode cohesive laws and fatigue damage parameters for cohesive crack propagation. The developed numerical model is compared and validated against sub-component testing on two different scale levels, using a Modified Tear Test (MTT) specimen geometry with simplified geometry and loading, and a more complex geometry sub-component specimen with a simplified Shear Web Disbond Test (SBDT). The work is carried out as part of the CORTIR-II project, funded by the Danish Ministry of Energy.

Crystallographic texture and the mechanical properties of API 5L X70 pipeline steel designated for an arctic environment

The aim of this research is to examine the effect of roughing and finishing reductions on crystallographic texture. Three rolling conditions were applied with the same total reduction but different combinations of the roughing and finishing reductions, identified by their finishing reductions as low (X7FL), medium (X7FM), and high (X7FH). Texture measurements showed significant inhomogeneity at the centreline region that had higher intensities of Epsilon, Alpha, and Gamma fibre textures compared to the quarter-thickness and surface layers. Drop Weight Tear Test (DWTT) indicated that X7FL and X7FM specimens, with a relatively higher fraction of texture components of {332}<113>, Gamma fibre, and Transformed Copper (TC), exhibited superior low-temperature impact toughness compared to the X7FH steel. The electrochemical hydrogen charging experiments showed that the internal hydrogen cracks appeared only in X7FL and X7FM steels due to the large presence of detrimental {001} grain orientation on surface layer, perpendicular to ND.

A novel methodology to characterise the ductile-to-brittle transition behaviour of pipeline steels using the dynamic tensile tear test

Brittle fracture control strategies for high-pressure pipelines are essential to prevent catastrophic failures resulting in significant economic losses and environmental damage. Typically, this is achieved by operating the pipeline well above the ductile-to-brittle transition temperature (DBTT). In general, a series of lab-scale fracture tests, such as the Charpy V-Notch (CVN) or Drop Weight Tear Test (DWTT), are performed at different temperatures to construct the ductile-to-brittle transition curve and determine the DBTT. However, when applied to high-grade steels, correction factors or additional criteria are often necessary to obtain satisfactory results. As an alternative lab-scale testing methodology to characterise high-grade steels, the Dynamic Tensile Tear Test (DT3) has been introduced. Recently, an experimental campaign was conducted with the implementation of a liquid nitrogen spray cooling system to characterise the ductile-to-brittle transition behaviour of X70 grade steel using the DT3 system. In this work, tests were performed at temperatures ranging from −80 °C to 25 °C. The transition behaviour was analysed using measured data, and fractography was performed using Scanning Electron Microscopy (SEM). The DBTT for the considered X70 grade steel was determined, and the performance of the DT3 methodology was compared to CVN and DWTT testing methods. Additionally, numerical models were created using Finite Element (FE) modelling and results were compared to the obtained experimental data. By implementing a stress-strain cleavage criterion in combination with the MBW material model, the models considered both ductile damage and failure, as well as brittle failure and mixed ductile-brittle failure. It can be concluded that the DT3-based transition curve provided a satisfactory DBTT prediction. Furthermore, numerical results showed a good correlation with experimental observations and demonstrated a similar transition behaviour.

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.