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Subramani Sockalingam
McNAIR Aerospace Center, University of South Carolina, USA

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Journal article
Published: 24 December 2020 in Composites Part A: Applied Science and Manufacturing
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This paper presents a novel experimental method for impacting microscale single fibers under dynamic multiaxial loading conditions. Experimental setup is developed by modifying a 0.25-inch diameter Hopkinson bar to directly impact fibers. Using this setup, ultrahigh molecular weight polyethylene (UHMWPE) Dyneema® SK76 single fibers, with average diameter 17 µm, are transversely impacted with indenter radii of 200 (blunt), 20 (sharp), and 2 (razor) µm at velocities of 10 and 20 m/s, corresponding to nominal strain rates of 4000–6300 s−1. Compared to high strain rate (1156 s−1) uniaxial tensile loading, significant reductions in failure strains are measured for transverse impact with blunt (34%), sharp (39%) and razor (61%) indenters. The reduction in tensile properties is attributed to strain rate and multiaxial stress-states induced by impactor geometries; while all three geometries induced transverse compression, sharp and razor induced a greater degree of transverse shear, observed by failure surfaces.

ACS Style

Frank David Thomas; Stephen L. Alexander; Tusit Weerasooriya; Subramani Sockalingam. Experimental investigation of the influence of dynamic multiaxial transverse loading on ultrahigh molecular weight polyethylene single fiber failure. Composites Part A: Applied Science and Manufacturing 2020, 142, 106250 .

AMA Style

Frank David Thomas, Stephen L. Alexander, Tusit Weerasooriya, Subramani Sockalingam. Experimental investigation of the influence of dynamic multiaxial transverse loading on ultrahigh molecular weight polyethylene single fiber failure. Composites Part A: Applied Science and Manufacturing. 2020; 142 ():106250.

Chicago/Turabian Style

Frank David Thomas; Stephen L. Alexander; Tusit Weerasooriya; Subramani Sockalingam. 2020. "Experimental investigation of the influence of dynamic multiaxial transverse loading on ultrahigh molecular weight polyethylene single fiber failure." Composites Part A: Applied Science and Manufacturing 142, no. : 106250.

Journal article
Published: 21 October 2020 in Composites Part B: Engineering
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This paper presents the automated fiber placement (AFP) manufacturing and high velocity impact response of hybrid pseudo-woven IM7/8552 carbon/epoxy composite laminates. Three 24 ply laminate configurations are studied where pseudo-woven sub-laminates are combined with traditional layups on the inside and outside, along with a third quasi-isotropic control laminate [45/90/-45/0]3s. Pseudo-woven sub-laminates are manufactured using a specialized in situ AFP process implementing tow skips. The pseudo-woven architecture is macroscopically heterogeneous with spatially varying fiber orientations both in-plane and through thickness resulting in multiple interfaces and an expanded design space. The impact experiments are performed according to ASTM D8101 in the range of 250–400 ft/s (76.2–121.92 m/s) using a single stage gas gun while utilizing digital image correlation and high-speed video to assess the laminate's response. Experimental results show that the hybridized configurations have a 45% reduction in back face surface damage, 19.5% less back face deflection and an increase of 5.5% in V50 velocity when compared to traditional laminate.

ACS Style

Cyrus Vakili Rad; Karan Kodagali; Julie Roark; Duane Revilock; Charles Ruggeri; Ramy Harik; Subramani Sockalingam. High velocity impact response of hybridized pseudo-woven carbon fiber composite architectures. Composites Part B: Engineering 2020, 203, 108478 .

AMA Style

Cyrus Vakili Rad, Karan Kodagali, Julie Roark, Duane Revilock, Charles Ruggeri, Ramy Harik, Subramani Sockalingam. High velocity impact response of hybridized pseudo-woven carbon fiber composite architectures. Composites Part B: Engineering. 2020; 203 ():108478.

Chicago/Turabian Style

Cyrus Vakili Rad; Karan Kodagali; Julie Roark; Duane Revilock; Charles Ruggeri; Ramy Harik; Subramani Sockalingam. 2020. "High velocity impact response of hybridized pseudo-woven carbon fiber composite architectures." Composites Part B: Engineering 203, no. : 108478.

Journal article
Published: 19 October 2020 in Fibers
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Ultra-high molecular weight polyethylene (UHMWPE) Dyneema® SK-76 fibers are widely used in personnel protection systems. Transverse ballistic impact onto these fibers results in complex multiaxial deformation modes such as axial tension, axial compression, transverse compression, and transverse shear. Previous experimental studies on single fibers have shown a degradation of tensile failure strain due to the presence of such multi-axial deformation modes. In this work, we study the presence and effects of such multi-axial stress-states on Dyneema® SK-76 yarns via transverse loading experiments. Quasi-static transverse loading experiments are conducted on Dyneema® SK-76 single yarn at different starting angles (5°, 10°, 15°, and 25°) and via four different indenter geometries: round (radius of curvature (ROC) = 3.8 mm), 200-micron, 20-micron, and razor blade (ROC ~2 micron). Additionally, transverse loading experiments were also conducted for a 0.30 cal. fragment simulating projectile (FSP) and compared to other indenters. Experimental results show that for the round, 200-micron indenter, and FSP geometry the yarn fails in tension with no degradation in axial failure strain compared to the uniaxial tensile failure strain of SK-76 yarn (2.58%). Whereas for the 20-micron indenter and razor blade, fibers fail progressively in transverse shear followed by progressive strength degradation of the yarn. Strength degradation of yarn occurs at relatively low strains of 0.6–0.7% with eventual failure of the yarn at approximately ~1.8% and ~1.5% strain for the 20-micron indenter and razor blade, respectively. Breaking angles (range of 10°–30°) are observed to have little effect on the failure strain for all indenter geometries.

ACS Style

Karan Shah; Subramani Sockalingam. Experimental Investigation of Transverse Loading Behavior of Ultra-High Molecular Weight Polyethylene Yarns. Fibers 2020, 8, 66 .

AMA Style

Karan Shah, Subramani Sockalingam. Experimental Investigation of Transverse Loading Behavior of Ultra-High Molecular Weight Polyethylene Yarns. Fibers. 2020; 8 (10):66.

Chicago/Turabian Style

Karan Shah; Subramani Sockalingam. 2020. "Experimental Investigation of Transverse Loading Behavior of Ultra-High Molecular Weight Polyethylene Yarns." Fibers 8, no. 10: 66.

Journal article
Published: 20 June 2020 in Composites Science and Technology
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This study investigates the high loading rate behavior of adhesively bonded carbon/epoxy composite joints under mode I loading. A computationally guided experimental setup is developed to study the mode-I behavior of composite joints in the range of quasi-static to high loading rates. A double cantilevered beam specimen with wedge insert type loading setup is used to conduct quasi-static and dynamic experiments. For the dynamic loading, a modified split Hopkinson bar is used to load the sample at high rates. The local deformation field is measured using high Spatio-temporal resolution digital image correlation (DIC). From the experiments, the mode-I energy release rate is calculated from the load, crack extension and crack root rotation data measured using load cell and DIC. A decrease in the initiation fracture toughness with increase in loading rate was observed which is attributed to the strain rate dependent behavior of the epoxy-based film adhesive. For both quasi-static and high loading rates, a mixed adhesive-cohesive failure is observed from the fracture surface analysis.

ACS Style

Suraj Ravindran; Subramani Sockalingam; Karan Kodagali; Addis Kidane; Michael A. Sutton; Brian Justusson; Jenna Pang. Mode-I behavior of adhesively bonded composite joints at high loading rates. Composites Science and Technology 2020, 198, 108310 .

AMA Style

Suraj Ravindran, Subramani Sockalingam, Karan Kodagali, Addis Kidane, Michael A. Sutton, Brian Justusson, Jenna Pang. Mode-I behavior of adhesively bonded composite joints at high loading rates. Composites Science and Technology. 2020; 198 ():108310.

Chicago/Turabian Style

Suraj Ravindran; Subramani Sockalingam; Karan Kodagali; Addis Kidane; Michael A. Sutton; Brian Justusson; Jenna Pang. 2020. "Mode-I behavior of adhesively bonded composite joints at high loading rates." Composites Science and Technology 198, no. : 108310.

Journal article
Published: 26 October 2019 in Computational Materials Science
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This paper investigates the inter-molecular interactions during tensile loading in ultrahigh molecular weight polyethylene (UHWMPE) single crystals at the atomistic scale. Molecular dynamics (MD) simulations of velocity controlled chain pullout are employed to study inter-molecular load transfer mechanisms. The transfer of tensile load is governed by van der Waals forces that dominate the inter-molecular shear interactions. The tensile stress build up occurs over a length of approximately 40c, where c is the lattice constant along the chain axis. Atomistic MD models incorporate the influence of surrounding neighboring atoms. Therefore, a nonlocal shear lag continuum model is developed for the first time to bridge length scales by extending the classical shear lag model of stress transfer in composites. The nonlocal model predictions correlate better with the MD results compared to the classical shear lag formulation. Combining the MD and shear lag model results, a bilinear mode II cohesive traction-separation behavior is identified to describe the inter-molecular interactions of the continuum with interface stiffness (2.38 GPa/nm), peak traction (0.14 GPa) and mode II fracture toughness (17 mJ/m2).

ACS Style

Sanjib C. Chowdhury; Subramani Sockalingam; John W. Gillespie Jr.. Inter-molecular interactions in ultrahigh molecular weight polyethylene single crystals. Computational Materials Science 2019, 172, 109360 .

AMA Style

Sanjib C. Chowdhury, Subramani Sockalingam, John W. Gillespie Jr.. Inter-molecular interactions in ultrahigh molecular weight polyethylene single crystals. Computational Materials Science. 2019; 172 ():109360.

Chicago/Turabian Style

Sanjib C. Chowdhury; Subramani Sockalingam; John W. Gillespie Jr.. 2019. "Inter-molecular interactions in ultrahigh molecular weight polyethylene single crystals." Computational Materials Science 172, no. : 109360.

Journal article
Published: 15 June 2019 in Defence Technology
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Ballistic impact induces complex stress states on fiber-based armor systems. During impact fibers undergo multiaxial loading which includes axial tension, axial compression, transverse compression, and transverse shear. Transverse compression induced by the projectile leads to permanent deformation and fibrillation resulting in degradation of material tensile strength. Previous work (Sockalingam et al. Textile Res. J 2018) showed a reduction in tensile strength of 20% for single Dyneema® SK76 fibers subjected to 77% nominal transverse compressive strains. Experimental investigation of quasi-static transverse compression on Dyneema® SK-76 yarns indicate an average of 4% reduction in tensile strength of yarns compressed to 77% nominal strains. This work uses finite element modeling techniques to understand this difference in residual tensile strength between single fibers and yarns observed in laterally unconstrained transverse compression experiments. Finite element study of the transverse compression response of single fibers and yarns indicate that local compressive strains developed in fibers within the yarn are much lower than the local strains developed in single fibers at a given applied nominal strain and may be the cause of less reduction in strength observed in yarns.

ACS Style

Karan Shah; Subramani Sockalingam. Effect of transverse compression on the residual tensile strength of ultrahigh molecular weight polyethylene (Dyneema® SK-76) yarns. Defence Technology 2019, 16, 35 -42.

AMA Style

Karan Shah, Subramani Sockalingam. Effect of transverse compression on the residual tensile strength of ultrahigh molecular weight polyethylene (Dyneema® SK-76) yarns. Defence Technology. 2019; 16 (1):35-42.

Chicago/Turabian Style

Karan Shah; Subramani Sockalingam. 2019. "Effect of transverse compression on the residual tensile strength of ultrahigh molecular weight polyethylene (Dyneema® SK-76) yarns." Defence Technology 16, no. 1: 35-42.

Research article
Published: 07 September 2018 in Textile Research Journal
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This article investigates the failure of ultra-high molecular weight polyethylene Dyneema® SK76 single fibers widely used in protective armor applications. Indenter geometry and the associated stress concentration are known to have a significant effect on the average axial tensile failure strain of Dyneema® SK76 fibers subjected to quasi-static transverse loading experiments by three indenter geometries. In this study, a 3D finite element model is developed to predict the degree of multiaxial loading at the location of fiber failure in these experiments. A failure criterion based on maximum axial tensile strain considering the statistical strength distribution and multiaxial loading (transverse compression and transverse shear) induced degradation effects is applied to predict the fiber failure. The influence of transverse compression on the tensile strength of single fibers is experimentally determined. The average failure strains predicted by the model are found to agree well with the experimental results indicating fiber failure may be initiated based on a gage length dependent maximum axial tensile strain in the fiber.

ACS Style

Subramani Sockalingam; Frank Thomas; Daniel Casem; Jr. John W Gillespie; Tusit Weerasooriya. Failure of Dyneema® SK76 single fiber under multiaxial transverse loading. Textile Research Journal 2018, 89, 2659 -2673.

AMA Style

Subramani Sockalingam, Frank Thomas, Daniel Casem, Jr. John W Gillespie, Tusit Weerasooriya. Failure of Dyneema® SK76 single fiber under multiaxial transverse loading. Textile Research Journal. 2018; 89 (13):2659-2673.

Chicago/Turabian Style

Subramani Sockalingam; Frank Thomas; Daniel Casem; Jr. John W Gillespie; Tusit Weerasooriya. 2018. "Failure of Dyneema® SK76 single fiber under multiaxial transverse loading." Textile Research Journal 89, no. 13: 2659-2673.

Conference paper
Published: 31 October 2017 in Fracture, Fatigue, Failure and Damage Evolution , Volume 3
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Ballistic impact onto fiber-based personnel protection armor systems induce multiaxial loading in the affected impact zone that includes axial tension, axial compression, transverse compression and transverse shear. The influence of the transverse compression response of ballistic fibers at high rates of loading is not well understood. In this study, high strain rate transverse compression response of aramid Kevlar KM2 and ultra-high molecular weight polyethylene (UHMWPE) Dyneema SK76 single fibers are investigated. Micron scale single fibers are transversely compressed at high loading rates in a small diameter Kolsky bar with optical interferometry to measure strains in the bars. The fibers exhibit a nonlinear inelastic behavior in transverse compression. Comparison of high rate and quasi-static response indicate a smaller contact area growth and a stiffer material response at higher rates of loading for both types of fibers.

ACS Style

Subramani Sockalingam; Daniel T. Casem; Tusit Weerasooriya; John W. Gillespie. High Strain Rate Transverse Compression Response of Ballistic Single Fibers. Fracture, Fatigue, Failure and Damage Evolution , Volume 3 2017, 51 -55.

AMA Style

Subramani Sockalingam, Daniel T. Casem, Tusit Weerasooriya, John W. Gillespie. High Strain Rate Transverse Compression Response of Ballistic Single Fibers. Fracture, Fatigue, Failure and Damage Evolution , Volume 3. 2017; ():51-55.

Chicago/Turabian Style

Subramani Sockalingam; Daniel T. Casem; Tusit Weerasooriya; John W. Gillespie. 2017. "High Strain Rate Transverse Compression Response of Ballistic Single Fibers." Fracture, Fatigue, Failure and Damage Evolution , Volume 3 , no. : 51-55.

Article
Published: 10 July 2017 in Journal of Dynamic Behavior of Materials
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This paper investigates the high strain rate transverse compression behavior of Kevlar® KM2 and ultra high molecular weight polyethylene Dyneema® SK76 single fibers widely used in protective components under ballistic and blast loading conditions. The micron scale fibers are compressed at strain rates in the range of 10,000–90,000 s−1 in a small (283 μm) diameter Kolsky bar with optical instrumentation. The nominal stress–strain response of single fibers exhibits nonlinear inelastic behavior under high rate transverse compression. The nonlinearity is due to both geometric and material behavior. The contact area growth at high rates is found to be smaller than at quasi-static loading leading to a stiffer material response at higher rates. The fiber material constitutive behavior is determined by removing the geometric nonlinearity due to the growing contact area. Atomic force microscopy analysis of the compressed fibers indicates less degree of fibrillation at high strain rates compared to quasi-static loading indicating that fibril properties and inter-fibrillar interactions could be strain rate dependent.

ACS Style

S. Sockalingam; D. Casem; T. Weerasooriya; P. McDaniel; J. Gillespie. Experimental Investigation of the High Strain Rate Transverse Compression Behavior of Ballistic Single Fibers. Journal of Dynamic Behavior of Materials 2017, 3, 474 -484.

AMA Style

S. Sockalingam, D. Casem, T. Weerasooriya, P. McDaniel, J. Gillespie. Experimental Investigation of the High Strain Rate Transverse Compression Behavior of Ballistic Single Fibers. Journal of Dynamic Behavior of Materials. 2017; 3 (3):474-484.

Chicago/Turabian Style

S. Sockalingam; D. Casem; T. Weerasooriya; P. McDaniel; J. Gillespie. 2017. "Experimental Investigation of the High Strain Rate Transverse Compression Behavior of Ballistic Single Fibers." Journal of Dynamic Behavior of Materials 3, no. 3: 474-484.

Journal article
Published: 14 February 2017 in Fibers
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Ballistic impact induces multiaxial loading on Kevlar® and polyethylene fibers used in protective armor systems. The influence of multiaxial loading on fiber failure is not well understood. Experiments show reduction in the tensile strength of these fibers after axial and transverse compression. In this paper, we use molecular dynamics (MD) simulations to explain and develop a fundamental understanding of this experimental observation since the property reduction mechanism evolves from the atomistic level. An all-atom MD method is used where bonded and non-bonded atomic interactions are described through a state-of-the-art reactive force field. Monotonic tension simulations in three principal directions of the models are conducted to determine the anisotropic elastic and strength properties. Then the models are subjected to multi-axial loads—axial compression, followed by axial tension and transverse compression, followed by axial tension. MD simulation results indicate that pre-compression distorts the crystal structure, inducing preloading of the covalent bonds and resulting in lower tensile properties.

ACS Style

Sanjib C. Chowdhury; Subramani Sockalingam; John W. Gillespie. Molecular Dynamics Modeling of the Effect of Axial and Transverse Compression on the Residual Tensile Properties of Ballistic Fiber. Fibers 2017, 5, 7 .

AMA Style

Sanjib C. Chowdhury, Subramani Sockalingam, John W. Gillespie. Molecular Dynamics Modeling of the Effect of Axial and Transverse Compression on the Residual Tensile Properties of Ballistic Fiber. Fibers. 2017; 5 (1):7.

Chicago/Turabian Style

Sanjib C. Chowdhury; Subramani Sockalingam; John W. Gillespie. 2017. "Molecular Dynamics Modeling of the Effect of Axial and Transverse Compression on the Residual Tensile Properties of Ballistic Fiber." Fibers 5, no. 1: 7.