Abstract
The dynamic failure behavior of multifilament high-performance yarns plays a crucial role in determining the impact resistance of advanced materials used in diverse applications such as aerospace, automotive, and protective textiles. The falling tower setup was designed to investigate the impact behavior of high-performance yarns. These models offer valuable insights into the fundamental mechanisms governing yarn failure. The force-time curves of different yarn samples under various impact energies show that Kevlar and Vectran® have the highest values of impact-resisting force, 21.9 and 21.6 N, respectively. The resisting impact energy reaches between 3.5 and 4 mJ. Enhancement of the multifilament yarn’s impact resistance was achieved through applications of silicone finishes or hybrid yarns, in which the impact resistance force and time to failure exhibited an increase across various yarn types. The ratio of impact yarn resisting force to yarn tenacity was determined to be 6.73%, 6.05%, 11.29%, and 1.71% for Vectran, Kevlar 29, polyester, and carbon yarns, respectively. Additionally, their specific yarn impact toughness was measured at 2.69, 1.32, 0.54, and 0.16 mJ/tex. The application of a 20% silicon coating increased their specific yarn impact toughness to 11.81, 5.79, 3.58, and 0.51 mJ/tex, respectively. Hybrid continuous fibers are composite materials that blend various fiber types, including carbon, Kevlar, Vectran®, or polyester, to form a material with enhanced impact absorption energy, such as in the case of Kevlar/PET or Carbon-PET. The outcomes of these investigations substantially contribute to enhancing multi-filament high-performance yarns in various practical applications in systems subjected to dynamic loads.
Introduction
Research on the impact of high-performance fibers is critical because it provides insight into standards across industries such as aerospace and aircraft. Enhance the safety and durability of the cabin and other aircraft components by creating corrosion-resistant structures. The automotive Industry improves the crash resistance of vehicle frames and bumpers by considering stiffness, energy absorption, and cost. Using impact-resistant carbon fiber composites to strengthen structures such as bridges and reinforced concrete against accidental loads or natural disasters. Military Applications: Development of light weapons and protective gear with optimized impact resistance for superior protection. Design spacecraft components with balanced thermal protection and impact resistance for space missions. Consequently, integrating insights from impact behavior research into design and engineering practices can lead to the development of safer, more durable, and higher-performing products across diverse industries.1–10 Evaluating the suitability of high-performance fiber used in composites for specific applications and considering impact performance during material suitability have high priority. Impact behavior studies can be incorporated into design and engineering practices to create safer, more sustainable, and more efficient products across industries.
The assessment and comprehension of dynamic yarn failure hold significance across diverse fields utilizing textiles and fiber-based materials. Particularly crucial in aerospace and automotive applications, the dynamic failure behavior of yarns is pivotal for ensuring the structural integrity and crashworthiness of components. These yarns, responsible for energy absorption during impacts, underscore the potentially catastrophic consequences of their failure. Key applications demanding a nuanced understanding include protective clothing (bulletproof vests, cut-resistant gloves), impact-resistant fabrics, composite materials, and sports equipment.11–18 In the aerospace and automotive sectors, yarns, often composed of high-performance fibers like carbon or aramid, play a pivotal role in structural components. Engineers leverage dynamic failure measurements to optimize composite designs, assess impact resistance, and predict failure modes under various loading conditions.15,16 Similarly, in sports and recreation, incorporating yarns into composite materials enhances equipment performance, offering benefits like improved impact resistance and energy absorption. 17 Recognizable materials like Kevlar find applications in sports equipment requiring strength and protection, such as hockey sticks and body armor. 18 Mountaineering equipment undergoes rigorous testing, especially dynamic and static testing of climbing ropes, as outlined by European standards like EN 892 and BS EN 17109:2020.19,20 In naval applications, synthetic materials replace traditional steel mooring cables, emphasizing the need for continuous studies on the mechanical characterization of fibers for synthetic cables, especially under dynamic loads.21–24 Yarns also find applications in industrial fabrics and geotextiles, where understanding dynamic failure characteristics is critical for durability and reliability in heavy-duty applications.25,26
The dynamic failure behavior of yarns is influenced by multiple factors, including yarn properties and loading conditions, impacting their performance in aerospace and automotive applications.27,28 However, ballistic performance in fabrics or yarns is reported to be a complex interplay of various factors, including multi-axial loading, stress gradients, and projectile characteristics.29–34 In applications subject to sudden and severe loads, such as crashes or impacts, yarns must effectively absorb energy to prevent catastrophic failure. Scientific understanding of high-performance textile materials in short-term dynamic events becomes paramount, considering their deviation from established behavior under static or quasi-static loading conditions.35–38 A comprehensive exploration of dynamic failure in yarns not only informs the design of materials for specific performance requirements but also enhances safety, durability, and overall performance across diverse industries.
In this investigation, drop tower tests were carried out to assess the performance of high-performance yarns, which include carbon fibers, Kevlar fibers, polyester fibers, and Vectran® fibers, under impact loading conditions. The goal was to identify the failure mechanisms of these yarns.
The study investigated several parameters that affect the impact strength of high-performance yarns. Diverse factors, such as impact energy and loading rates, were systematically examined to analyze the dynamic failure behavior of these yarns. Additionally, various methods were suggested to enhance the impact resistance of multifilament yarns, aiming to improve their overall performance.
Materials and methods
Material
In this work, several yarn samples were made of the following with the specifications given in Table 1. The yarn testing was carried out according to ASTM (yarn strength D 2256-02 and yarn count ASTM D1059).
The specifications of the yarns (ASTM D 2256-02).
Coefficient of variation (CV %).
Set up for measuring the dynamic yarn strength
The impact tests were conducted using a dedicated setup designed for this purpose, utilizing a falling-weight tower as depicted in Figure 1. The application of drop-weight impact machines 39 in medium strain rate tensile testing was reported for a variety of materials, including textiles. 40 The drop weight impact test method was intended to be used with the falling weight tower arrangement. which was the “free fall,” or the dropping of weight in a vertical direction. Once more, impact energy may be computed assuming no guiding system and no friction science when height and weight are known. Since the falling weight either stopped dead on the test specimen or destroyed it completely in pulling through, the only results that could be obtained were of a pass/fail nature. When an impulse loading from a strain wave is delivered to a structure, it produces an instantaneous velocity change: momentum is acquired and the structure gains kinetic energy, which is converted to strain energy while the weave structure deforms. The yarn sample will be fixed in the upper and lower jaws. The upper jaw is fixed to load the transducer, while the lower jaw is attached to the falling weight. The value of the energy applied to the tested specimen is:
Where m is the mass of the falling weight, V is the final velocity of the falling weight before impacting the sample
Where W is the striker weight (kg) W = mg, g is the gravity acceleration (m/s 2 ), h is the fall height (m),
Falling weight tower setup.
If the impact failure energy E yarn impact resistance, of yarn is more than the Efalling weight (J), the yarn will be able to absorb the impact energy without failure. If the Efalling weight is greater than the yarn failure Eyarn impact resistance will happen.
The load transducer records the impact load as a function of time.
The residual energy is
Where:
Efalling weight residual (J) is the falling weight residual energy, Efalling weight is falling weight (J),
Eyarn impact resistance is yarn impact energy (J).
Efalling weight residual will be absorbed through a special damping system that can stop the weight from continuing to fall.
The yarn was deformed under different strain loading through the change in the value of the impact velocity, by changing the falling height and keeping the Efalling weight constant or changing Efalling weight, keeping the impact velocity constant. The strain rate in the case of changing the impact velocity will vary as the impact speed increases while when the value of the impact energy increases the initial impact stress will proportionally increase.
Different materials can behave in quite different ways in impact when compared with static loading conditions. The time of the yarn failure was measured using an infrared sensor (Passive Infrared (PIR) sensor).
Impact test
Figure 1 shows the details of the design of the falling weight setup.
Impact test procedure
The impact test itself is based on the application of a mass in free fall from a certain height of fall. The specimens for the impact test are 100 mm long, corresponding to L (Figure 2). The impact load is released at a height of free fall of 500, 750, and 1000 mm. The equipment has a load cell at the top, where the upper jaw is fixed, and is capable of capturing force data. All specimens are subjected to impact under similar conditions until rupture under the free fall weight.
Scheme application of impact mass.
To measure the amount of force and energy required to fracture a standardized yarn specimen under a single impact by the falling weight. The standard procedure for conducting the impact test typically involves:
The weight is raised to a specific height, creating potential energy (500, 750, and 1000 mm). The value of mass and the initial height were chosen according to the potential energy required to cause failure to the yarn specimen. Then the weight is released, falling freely downward and impacting the specimen when it reaches the predetermined height (h). The impact of the weight causes the specimen to fracture. The value of the instantaneous force acting on the specimen during fracture is measured using a force transducer, and the energy value is typically reported in joules (J). Ten samples of the material were prepared from each type of yarn.
Enhances the impact resistance of multifilament yarns
Several methods exist to enhance the impact resistance of yarns. 41 In the experimental work, attempts were made to improve the impact resistance of multifilament yarns through silicone gel coating and hybrid yarn techniques, utilizing combinations such as Vectran/carbon, Kevlar/PET, Kevlar/carbon, and carbon/PET. The experimental flow chart is given in Table 2.
The experimental flow chart of the tested samples.
Results and discussions
Impact force versus time analysis
When a yarn is subjected to an impulse load, the load is transmitted through the yarn as a wave travels along the length of the yarn and causes it to deform. The deformation of the yarn results in an increase in tension, which, as shown in Figure 3, can cause the yarn to extend until it breaks if the load is too great for its dynamic strength. Impulse loading results in stress within the yarn. In the case of multifilament yarn, the filament’s breakage may occur at different instances depending on the impact-generating shock waves that travel along each filament. These shock waves can be transmitted through the yarn and exhibit dynamic behavior, meaning their response to impulse loading can be complex. Several factors, such as the mechanical properties of the filaments, their diameter, and the angle at which the force is applied, also influence their behavior.
The force-time curve of different yarn samples.
The force-time curve in the case of impact loading will have different shapes depending on the property of the yarn, the specification, and the applied impact energy. Figure 3 shows the force-time curve for different types of yarns. While Figure 4 shows the general shape of the force-time curve.
The force-time curve.
A general analysis of a typical yarn force-time curve during impact loading: during the initial contact of the yarn, the force-time curve starts with a baseline force value when the impact begins. The curve will typically start with a sharp, sudden increase in force when the impact is applied. This initial spike in force occurs as the yarn absorbs the energy of the impact. When a material is subjected to a high strain rate, such as in a sudden impact, it experiences different mechanical behavior compared to when it is subjected to a low strain rate. An increase in strain rate leads to an increase in the strength of the material. This is because higher strain rates promote dislocation movement and increase the resistance to deformation; materials tend to exhibit reduced ductility.
Ultimately, if the impact is severe enough or if the yarn’s tensile strength is exceeded, the force-time curve will show a rapid drop as the yarn breaks. This is a crucial point in the analysis, as it indicates the yarn’s ultimate impact on tensile strength.
Several factors, including the speed of impact and the velocity of yarn strain propagation, influence the increase in yarn impact resistance force.
The magnitude of the peak impact resistance force depends on the yarn’s mechanical properties, including its tensile strength, modulus, and toughness, due to the role these properties play in determining the yarn’s ability to absorb and distribute energy during an impact. The ability of a material to absorb energy and deform plastically before fracturing. Yarn with higher toughness can absorb more energy during an impact event. This is crucial for impact resistance, as the yarn needs to absorb and dissipate the energy generated during an impact to minimize damage.
Peak force occurs when the force-time curve reaches its maximum value, representing the peak force experienced by the yarn. This peak force indicates the maximum resistance offered by the yarn to the applied impact force. The magnitude of the peak force depends on the yarn’s mechanical properties, including its tensile strength, modulus, and toughness. After reaching its peak force, the force starts to decrease gradually. This decrease in force can occur due to factors such as yarn deformation, fiber slippage, or energy dissipation within the yarn structure. The rate of force decrement is influenced by the yarn’s resilience, filament-filament interactions, and frictional properties. In the case of the impact, if energy is higher than the yarn impact resistance, energy failure will occur, or following the force decrement, a residual force may remain, indicating the sustained resistance of the yarn to the impact. The factors influencing the decline in force after an impact on a yarn. The rate at which the force diminishes is affected by the yarn’s resilience, interactions between individual filaments, and its frictional properties. If, during the impact, the energy surpasses the yarn’s capacity for impact resistance, failure will occur. Alternatively, even after the force starts to decline, there might be residual force, indicating that the yarn continues to resist the impact, showcasing its ability to withstand the force applied. The magnitude of the residual force depends on the extent of yarn deformation and filament-filament bonding. In some cases, after the initial force decrement, there might be a partial or complete force recovery. This occurs when the yarn exhibits a degree of elastic recovery, regaining some of its original shape and restoring a portion of the initial force. The force recovery is influenced by the yarn’s elastic properties and the magnitude of deformation during impact.
The shape of the force-time curve depends on the response of the yarn to the applied impact load. It was revealed that the yarn, during loading, will pass through several phases.42,43 The time curve of impact force can be divided into three stages:
When the weight is applied to the yarn at zero time, the impact resistance force reaches its peak value rapidly under the impact impulse.
After the initial stage, Depending on the characteristics of the yarn, it may also observe some oscillations in the force-time curve as the yarn vibrates in response to the impact. The material impact resistance force mainly works at this stage. The duration depends on the type of material as well as the variability of the filament impact resistance force.
The impact resistance force begins to decay after the stable stage, and finally the impact resistance force decreases to zero at the yarn failure.
It’s important to note that the specific shape and characteristics of the force-time curve can vary depending on factors such as yarn material toughness, its structure, impact speed, and the structure of the impacting yarns.
Figure 5(a)–(d) shows the force and energy versus time for the different types of yarns, which indicates the advantage of Kevlar and Vectran yarns over the other tested yarns.
(a–d) Force-time and absorbing energy-time of the different yarns, impact energy 11 J.
Due to the high failure strain, the impact loading of the filaments is increased, mainly because of the slippage of molecular chains. Both the covalent and van der Waals bonds along the fracture surface are broken. At high strain rates, the time duration for a bond to remain at a specific strain level becomes shorter, allowing less time for intermolecular slippage to happen. As a result, the likelihood of van der Waals bond breakage reduces, while that of covalent bond scission increases with the strain rate. This increase in covalent bond scission dominates over intermolecular slippage at high strain rates, leading to a decrease in failure strain and an increase in tensile strength. The strength of a covalent bond depends on the types of atoms involved and the number of shared electrons.35,40,43,44
Fibrillation of fibers and intermolecular shear slippage involving the breakage of van der Waals bonds are dominant in this post-peak region. As the strain rate increases, the single yarns fail in a more brittle manner by exhibiting a sharp drop in stress after the peak (Zone III).
In impact tests using drop towers, the samples of the yarns are subjected to controlled impacts at constant speeds while the total kinetic energy is constant. The yarn under impact force will be elongated at a high strain rate in a short period of time. The yarn’s failure depends on its material strain sensitivity. When a yarn is subjected to mechanical stress, it experiences strain, which can lead to the activation of mechanisms within the material, such as microstructural rearrangements and intermolecular interactions. The way these mechanisms respond to strain and deformation is influenced by the material’s strain sensitivity. A material with a high strain sensitivity may exhibit greater changes in its properties (e.g. tensile strength, Young’s modulus, elongation) as it deforms, making it more inclined to failure under certain conditions. Conversely, a material with low strain sensitivity may be more resistant to deformation-induced changes in its properties and may exhibit better mechanical performance under similar conditions. 45 Carbon yarns are known for their exceptional stiffness and high tensile strength. When exposed to impact forces, carbon yarns tend to resist deformation and absorb minimal energy through stretching, making them more prone to fracture or shattering under sudden, high-energy impacts. Consequently, carbon yarns may not efficiently absorb impact energy compared to other materials. In contrast, Kevlar yarns are renowned for their superior impact resistance. They can effectively absorb substantial energy by deforming and stretching when subjected to impact forces. The flexibility of Kevlar filaments surpasses that of carbon fiber, enabling it to endure bending during impact processes. Similarly, Vectran yarns are recognized for their adeptness at absorbing and dissipating impact energy efficiently. Polyester yarns possess a moderate level of impact resistance; they can absorb and dissipate some energy through deformation but may not perform as adeptly as Kevlar in high-impact scenarios. Polyester yarns are relatively flexible and can withstand moderate bending and stretching during impacts.
Analysis of the impact energy effect
Figure 6 shows the force-time curve for different types of yarns under various impact energies, which are varied through the change in the value of the falling height (h).
(a and b): The force-time curves of different yarn samples under various impact energies: (a) impact energy 6.1 J and (b) impact energy 11 J.
As illustrated in Figure 6, the total yarn failure time reduces as the speed of impact increases, and high strain rates can decrease fracture toughness, making materials more sensitive to brittle fracture. As a result, at higher strain rates, materials tend to absorb less energy before failure. Strain rate refers to the rate at which a material is subjected to deformation or strain. It is a measure of how quickly the material is being stretched. The strain rate has a significant impact on the mechanical properties of materials. 45 The increase in the impact energy leads to a reduction in the impact time and an increase in the value of the impact resistance force for all types of yarns.
Effect of material mechanical properties on impact resistance energy
Yarn Young’s modulus
The force-time curve of impacted yarns, Figure 6, depends on the internal structure of both filament material and yarn specifications, as well as the impact energy and impact velocity. When yarn is subjected to impact, it undergoes deformation and stress distribution within its internal structure. Based on the distinct material properties and yarn specifications, the force-time curve may manifest diverse shapes and characteristics, including peak force, impact duration, and overall response pattern. 35 The material properties of the yarn’s filaments, encompassing their tensile strength, modulus, and elasticity, significantly contribute to shaping the yarn’s response to impact forces. This is in addition to yarn specifications, such as the yarn’s construction details—like the number of filaments, twist level, yarn diameter, and fiber type which can impact its force-time curve during an impact. The amount of energy transferred to the yarn during impact affects the force-time curve. Higher impact energy generally results in greater force exerted on the yarn. The speed at which the impact occurs also affects the force-time curve. Higher impact velocities can lead to different responses compared to lower velocities. 44 These factors were discussed for the chosen types of fibers: Vectran®, Kevlar, carbon, and polyester continuous filament yarns. The key differences between these materials lie in their compositions, manufacturing processes, and crystalline or amorphous structures. Carbon fibers are composed of carbon atoms arranged in a long, tightly bound chain, which gives them exceptional strength and stiffness properties. Kevlar is an aramid fiber composed of long chains of molecules with alternating amide groups. It has a highly oriented and crystalline structure, which contributes to its strength and resistance to impact. Vectran is another fiber, but it differs from Kevlar in its chemical structure. Vectran is composed of liquid crystal polymer (LCP) molecules. Polyester fibers are made from petrochemical-based polymers, typically polyethylene terephthalate (PET). Polyester fibers have an amorphous structure with randomly oriented polymer chains.
These properties will be reflected in their impact force-time curve.46–49 The impact force-time curve in the case of impact loading will have different shapes depending on the property of the tow, the specification, and the value of the impact energy.
Figure 7 shows the relation between the impact resistance force (IP) MPa and the yarn Young’s modulus (E) GPa ratio of different fibers. This suggests that polyester has the highest ratio of IP/E, whereas carbon fiber demonstrates the least value. This may be due to the effect of other factors, such as the toughness of the material under the impact force and the yarn’s extensibility. A higher impact resistance means the material can absorb more energy before failing. The impact resistance of a synthetic fiber also depends on its composition, internal structure, and other factors beyond Young’s modulus. If a material is too stiff (high Young’s modulus), such as carbon yarn, it may become brittle and fail more easily upon impact, as it cannot absorb and dissipate the energy.
The ratio of the IP/E of different yarns.
Yarn impact toughness
The toughness is defined as the area under the entire stress-strain curve. Toughness quantifies the potential of yarns to absorb energy under tensile loading. Impact toughness, on the other hand, measures a material’s ability to resist fracture under sudden, high-velocity loading conditions, such as an impact or a shock. It is determined by the amount of energy the material can absorb before fracturing during an impact test. Table 3 gives the different properties of the samples. 43 The percentage of specific yarn (impact-resisting force/tenacity) indicates that polyester yarn has the highest ratio, while carbon fibers have the lowest percentage.
Experimental results of the yarn impact properties.
Figure 8 shows the impact toughness of the different yarns indicating that Vectran yarns have the highest impact toughness while carbon yarn has the lowest.
Yarns impact the toughness of Vectran, Kevlar, Carbon, and Polyester yarns.
Both impact resistance force and impact toughness are related to a material’s performance under impact loads; impact toughness specifically measures a material’s ability to deform and absorb energy before fracturing, whereas impact resistance is a more general term used to describe a material’s overall resistance to impact and impact loading.
The impact resistance of a material is closely correlated with its impact toughness. A material with high impact toughness will generally exhibit better impact resistance, as it can absorb more energy before failure. In contrast, a material with low impact toughness is more likely to fail or fracture upon impact, indicating poor impact resistance. Tough materials can absorb and distribute energy, preventing the concentration of stress that could lead to failure. In contrast, brittle materials have lower impact toughness and are more prone to catastrophic failure under impact loading.
Figure 9 shows the relation between the yarn impact resistance and impact toughness, which indicates that Vectran fibers have the best impact resistance force and carbon yarns have the lowest value.
Impact resistance force versus the impact toughness of the yarns.
Yarn impact resistance
In general, impact stress is the stress experienced by the yarn when it is subjected to sudden or dynamic loads, such as impact or shock. Tensile stress, on the other hand, refers to the stress exerted on the yarn when it is subjected to an impact force.
The impact stress/tensile stress ratio can vary significantly depending on the specific yarn characteristics. Yarns designed for high-impact resistance, such as those used in applications like ropes, seat belts, or ballistic materials, may have a higher impact stress/tensile stress ratio. These yarns are engineered to absorb and dissipate energy during impact loading conditions. In contrast, yarns with a lower impact stress/tensile stress ratio may be more suitable for applications where steady tensile strength is the primary requirement. If carbon fiber is excluded due to the difference in the mechanism of fiber breakage, a highly positive correlation was found between the impact yarn force and the yarn strength, as shown in Figure 10.
Yarn impact resistance versus yarn strength.
Failure analysis of yarns under impact force
Analyzing the failure of yarns under an impact force involves understanding the behavior of yarns when subjected to sudden, high-intensity loads. The impact force can cause different types of failure, depending on the material and its properties. Common failure modes for yarns under impact might include fracture, where the yarn may break into multiple pieces due to excessive force; irregular cut; clear cut; splitting, when the yarn may split along its length without complete fracture; and splintering and pulling out short filaments. Figure 11 gives microscopy images showing the fractured ends of yarns.
Microscopy images of the fractured ends of impacted yarns.
The polyester multifilament yarn has a finite energy absorption capacity. Intense impact loading can result in a rapid release of energy that exceeds the material’s ability to absorb or dissipate, leading to failure. Failure modes, including filament fracture, filament pull-out, and filament untangling, are illustrated in photo a in Figure 11. The failure mechanism of Kevlar multi-filament yarn under impact tension loading is associated with the interaction between fibers and the failure of individual filaments. Filament fracture, filament pull-out, and filament unraveling are observed failure modes, illustrated in photo b in Figure 11. For Vectran multi-filament yarn, the mechanism of failure during impact tension loading involves progressive damage leading to the final failure of the yarn. The filaments undergo nonlinear damage until reaching the point of ultimate failure under tension load, as depicted in photo c in Figure 11. In the case of carbon fiber under impact tension loading, the failure mechanism is influenced by several factors. The application of sudden and intense tensile force results in the brittle fracture behavior of carbon fibers. The impact force induces stress waves that propagate through the material, leading to rapid and often catastrophic failure. Carbon fibers may experience a brittle fracture, characterized by the propagation of a wave of deformation along their length, resulting in a sudden and complete failure, as shown in photo d in Figure 11.
Enhancement of the multifilament yarn’s impact resistance
Multifilament yarns are widely used in various industries, ranging from textiles to automotive and aerospace applications, due to their high strength and flexibility. However, the impact resistance of multifilament yarns is crucial in scenarios where they are subjected to external forces and potential damage. To improve the impact resistance of multifilament yarns, various finishes have been developed and applied.
To enhance it, as suggested, apply a yarn finish to increase the integrity of the filament during the impact, such as silicone finishes, which create a protective coating on the yarn surface. Silicone finishes can improve the impact resistance of the filament by providing a protective layer. This layer acts as a barrier, absorbing and distributing the impact energy, thus reducing the likelihood of filament breakage or damage. The silicon coat was hand-layered on the yarn using a specialized technique where the yarn is dipped into liquid silicon and then carefully layered by hand to ensure an even and consistent coating. Silicone finishes, which create a protective coating on the yarn surface, are known to enhance impact resistance. They improve durability by adding a layer of protection against external forces. 50 These finishes create flexible layers on the yarn, offering enhanced resistance to impact damage. In this work, the percentage of the finish added in all cases was 20% of commercial silicon (silicone polydimethylsiloxane (PDMS)). Figure 12 shows the effect of the application of a silicone finish on the force-time curve diagram of the different yarns. Both the impact-resisting force and the time of failure increased for the different types of yarns.
Effect of application of silicone on the impact force-time curve of different yarns.
Figure 13 gives microscopy images of the fractured ends of yarn, indicating intrafilamentary slippage under an impact load. The filaments in the yarn may experience slippage between each other. This phenomenon can weaken the yarn’s overall integrity and negatively affect its load-bearing capacity. The multifilament yarn is split, and the different filaments were cut at different instances during the application of the impact load zone II.
The images show the fractured ends of yarns.
The failure mechanism of silicon-coated multifilament yarn under impact load involves several stages that depend on the specific properties of the yarn and the impact conditions.
When an impact load is applied to the yarn, it undergoes rapid deformation as the kinetic energy is transferred to the material. The silicon coating may initially act as a protective layer, absorbing some of the impact energy and distributing it over the filaments.
From the analysis of the failure of the impacted yarns (Figures 12 and 13), it was revealed that the failure modes are completely different from those without silicon gill coating. The presence of a silicon gill coating will hold the filament together and increase the interfilamentous friction and the redistribution of the impact stress, which leads to an increase in the impact resistance energy of the multifilament yarns and, consequently, the filament cohesion, resulting in higher yarn impact resistance. On average, the impact resistance force increased by 150% by using a silicon gill coating. As shown in Figure 13, which indicates that most of the ends of the yarn after it has been impacted show a clear cut, This explains the increase in the impact resistance force of the coated yarns due to the instant participation of most of the filaments in resisting the impacted load. The breakage of the filaments in zone II is compacted together.
Mechanism of failure of the hybrid yarns
Hybrid continuous fiber yarns are composite materials made up of different types of yarns, such as carbon, Kevlar, Vectran, or PET, that are combined to create a stronger and more durable material. When subjected to an impact force, the failure mechanism of these yarns can be affected by the magnitude of the force. The use of hybrid yarns can result in a lighter-weight combination material, which is desirable in applications where weight reduction is important, such as in the aerospace or automotive industries. The hybrid yarns are composed of two yarns aligned parallel to each other and clamped by the upper and lower jaws.
When the impact force is applied to the yarns, it induces stress waves that propagate through the material. The orientation of fibers affects how these stress waves interact with the material and can either enhance or hinder the material’s ability to resist deformation and fracture.
Specifically, if the fibers are aligned with the direction of the impact force, they can effectively absorb and distribute the stress waves, resulting in improved impact resistance. Therefore, optimizing the fiber orientation in hybrid continuous fiber yarns is essential for achieving superior impact performance. The behavior of the failure of the hybrid yarns depends on the strain propagation speed of each component.51–55 In Figure 14, the force-time curve illustrates that, across various combinations of yarns, the measured impact resistance force consistently rises when hybrid yarns are employed. The time taken for impact failure increased for all yarn groups except when polyester yarns were utilized, potentially attributed to the significant difference in breaking extension among the hybrid yarns.
The force-time curve of different combinations of yarns: (a) Vectran-Carbon, (b) Carbon-PET, (c) Kevlar-Carbon, and (d) Kevlar- PET.
The combination of the different yarns together affects the impact of strength and toughness. For example, in the case of carbon/Kevlar combinations, this configuration finds application in certain weaving designs where both the warp and weft yarn include one carbon yarn alongside the Kevlar yarn. The weft insertion follows a pattern of one Kevlar yarn for the initial pick, followed by the insertion of a carbon yarn for the second pick. This particular combination is more extensively utilized than others, proving well-suited for a diverse range of applications. It is particularly advantageous in numerous high-performance and high-impact scenarios, including but not limited to boat building, automotive manufacturing, military applications, racing, sporting goods, and the production of high-strength paneling.
Hybrid continuous Kevlar/carbon fiber yarns offer enhanced impact resistance by combining the strengths of Kevlar and carbon fibers. Kevlar absorbs and distributes impact energy, while carbon fibers provide reinforcement and prevent cracking. The hybrid material shows superior toughness compared to using either fiber alone. However, the failure mechanism under impact is complex and influenced by factors like fiber orientation, volume fraction, and impact force type. The strain wave generated during the impact significantly affects the mechanical properties of the yarn, leading to changes in strength, stiffness, and elasticity. The distinct failure characteristics of Kevlar and carbon fibers involve Kevlar’s high tensile strength and energy absorption, leading to deformation and potential fracture, while carbon fibers exhibit brittle fracture behavior under high-impact forces. This refers to the propagation of a wave of deformation that travels along the length of the yarn when it is subjected to an impact load. Understanding these mechanisms helps predict yarn failure under specific conditions.53–55 In general, a larger and longer-lasting strain wave will lead to more significant changes in the mechanical properties of the yarn. This can include a decrease in strength, an increase in stiffness, and a reduction in elasticity. 37 This refers to the propagation of a wave of deformation that travels along the length of the yarn when it is subjected to an impact load. This phenomenon can be used to predict the failure of the yarn under certain conditions.
The value of impact energy is often a key parameter considered in the study of impact phenomena. The specific impact energy, which quantifies the amount of energy absorbed by a material during impact per unit mass, is particularly important for comparing the impact resistance of different samples. In Table 4, the specific impact energy values are provided to facilitate the comparison of the various samples in terms of their ability to absorb impact energy relative to their mass. This allows for a more meaningful assessment of their impact.
Yarn-specific toughness energy for impacted yarns.
A comparison of the yarn toughness in the case of using silicon-coated yarn and when a combination of different yarns is tested. The use of Vectran®, Kevlar®, or even polyester yarns improves the yarn toughness of the carbon yarns, as shown in Figure 14.
The use of silicon-coated yarn significantly affects the specific impact toughness energy more than in the case of hybrid yarn combinations. Silicon coating may have better compatibility with the base yarn material, ensuring optimal adhesion and integration. This compatibility can enhance the overall toughness and energy of the yarn, especially under dynamic impact conditions.
For hybrid yarns, the behavior of carbon-Vectran as carbon-Kevlar results in the specific energy being reduced. Carbon fibers, known for their high stiffness and strength, have different mechanical properties compared to Vectran and Kevlar fibers, which are renowned for their high tensile strength and energy absorption capabilities. When combined, the dissimilar materials may not effectively complement each other’s properties, leading to a reduction in overall specific energy. All the hybrid yarns with PET yarn indicate that their presence increases both the impact force and the failure time, resulting in higher toughness. These results were noticed for all combinations of carbon-PET and Kevlar-PET, as given in Table 4. Vectran and Kevlar fibers are known for their high-impact tensile strength and stiffness, while polyester fibers exhibit good energy absorption and elongation characteristics that increase the ratio of yarn (impact resisting force/tenacity). When combined in a hybrid yarn, the complementary properties of Vectran/Kevlar and polyester fibers synergistically contribute to the enhanced energy absorption abilities of the polyester fibers. Vectran/Kevlar fibers can provide structural integrity and resistance to high loads, while polyester fibers can absorb impact energy through controlled deformation and elongation.
Conclusion
The study delved into the dynamic failure behaviors of high-performance yarns, including Vectran, Kevlar, polyester, and carbon, shedding light on their distinct responses to impact loading. Through careful analysis, we unveiled the intricate mechanics governing these materials’ failure patterns. We observed that the unique molecular structures and orientations of Vectran and Kevlar contribute to their specific failure mechanisms, while carbon yarns exhibit brittle failure due to their composite nature. Notably, polyester’s viscoelastic properties make it sensitive to strain rate, potentially matching carbon fibers in impact resistance. Additionally, the application of silicon coating emerged as a notable advancement, enhancing impact resistance and expanding potential applications, depending on material specifics. Hybrid yarns, particularly Kevlar and Vectran, showcased superior ballistic and impact-resilient properties, while carbon fibers, despite their strength, are better suited to low-impact applications due to their brittleness. The evaluation of impact yarn resisting force and specific yarn impact toughness revealed significant differences among the materials, further highlighting their distinct characteristics. With a 20% silicon coating, specific yarn impact toughness saw notable improvements across all materials. The impact yarn resisting force/yarn tenacity ratio was found to be 6.73%, 6.05%, 11.29%, and 1.71% for Vectran, Kevlar 29, polyester, and carbon yarns, respectively. Meanwhile, their specific yarn impact toughness was 2.69, 1.32, 0.54, and 0.16 mJ/tex. Silicon-coated yarns of 20% increase their specific yarn impact toughness up to 11.81, 5.79, 3.58, and 0.51 mJ/tex. Future work extends the analysis to investigate the impact behavior of composite materials reinforced with multi-filament high-performance yarns. explore how the properties of the yarns influence the overall impact resistance of composite structures and develop strategies to optimize composite design for enhanced impact performance. This research underscores the importance of understanding material behaviors under dynamic loading conditions, paving the way for the development of advanced materials with enhanced impact resistance and broader applications.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
