ABSTRACT
Hybrid composites are expanding applications in cutting-edge technology industries, which need materials capable of meeting combined properties in order to guarantee high performance and cost-effectiveness. This original article aimed for the first time to investigate the hybrid laminated composite thermal behavior, made of two types of fibers: synthetic Twaron® fabric and natural curaua non-woven mat, reinforcing epoxy matrix. The composite processing was based on the ballistic helmets methodology from the North American Personal Armor System for Ground Troops, currently used by the Brazilian Army, aiming at reduced costs, total weight, and environmental impact associated with the material without compromising ballistic performance. Thermal properties of plain epoxy, aramid fabric, and curaua mat were evaluated, as well as the other five configurations of hybrid laminated composites. These properties were compared using thermogravimetric analysis (TGA) with its derivative (DTG), differential thermal analysis (DTA), and thermomechanical analysis (TMA). The results showed that the plain epoxy begins thermal degradation at 208 °C while the curaua mat at 231 °C and the aramid fabric at 477 °C. The hybrid laminated composites curves showed two or three inflections in terms of mass loss. The only sample that underwent thermal expansion was the five-aramid and three-curaua layers composite. In the third analyzed temperature interval, related to the glass transition temperature of the composites, there was, in general, an increasing thermal stability behavior.
ABSTRACT
Curaua, as a leaf-based natural fiber, appears to be a promising component with aramid fabric reinforcement of hybrid composites. This work deals with the investigation of flexural, impact and elastic properties of non-woven curaua-aramid fabric hybrid epoxy composites. Five configurations of hybrid composites in a curaua non-woven mat with an increasing quantity of layers, up to four layers, were laminated through the conventional hand lay-up method. The proposed configurations were idealized with at least 60 wt% reinforcement in the non-alternating configuration. As a result, it was observed that the flexural strength decreased by 33% and the flexural modulus by 56%. In addition, the energy absorbed in the Charpy impact also decreased in the same proportion as the replaced amount of aramid. Through the impulse excitation technique, it was possible observe that the replacement of the aramid layers with the curaua layers resulted in decreased elastic properties. However, reduction maps revealed proportional advantages in hybridizing the curaua with the aramid fiber. Moreover, the hybrid composite produced an almost continuous and homogeneous material, reducing the possibility of delamination and transverse deformation, which revealed an impact-resistant performance.
ABSTRACT
A typical ballistic protection helmet for ground military troops has an inside laminate polymer composite reinforced with 19 layers of the aramid, which are neither recyclable or biodegradable and are relatively expensive. The hybridization of synthetic aramid with a natural lignocellulosic fiber (NLF) can provide a lower cost and desirable sustainability to the helmet. In the present work, the curaua fiber, one of the strongest NLFs, is, for the first time, considered in non-woven mat layers to partially replace the aramid woven fabric layers. To investigate the possible advantage of this replacement, the tensile and impact properties of aramid/curaua hybrid laminated composites intended for ballistic helmets, in which up to four layers of curaua were substituted for the aramid, were evaluated. Tensile strength, toughness, and elastic modulus decreased with the replacement of the aramid while the deformation of rupture was improved for the replacement of nine aramid layers by two layers of curaua. Preliminary impact tests corroborate the decreasing tendency found in the tensile properties with the replacement of the aramid by curaua. Novel proposed Reduction Maps showed that, except for the replacement of four aramid layers by one layer of curaua, the decrease percentage of any tensile property value was lower than the corresponding volume percentage of replaced aramid, which revealed advantageous hybridization for the replacement of nine or more aramid layers.
ABSTRACT
This study aims to develop a lightweight ballistic helmet based on nanocomposite with matrix of the copolymer of benzoxazine with an urethane prepolymer [poly(BA-a-co-PU)], at mass ratio 80/20, reinforced with aramid fabric and multi-walled carbon nanotubes (MWCNTs). This has a protection level II according to the National Institute of Justice (NIJ) 0106.01 standard. The effects of MWCNTs mass content in a range of 0 to 2 wt% on tensile, physical and ballistic impact properties of the nanocomposite were investigated. The results revealed that the introduction of MWCNTs enhanced the tensile strength and energy at break of the nanocomposite; the highest values were obtained at 0.25 wt%. In addition, the nanocomposite laminate with 20 plies of aramid fabric showed the lowest back face deformation of 8 mm which was much lower than that specified by the NIJ standard. According to Military Standard (MIL-STD) 662F, the simulation prediction revealed that the ballistic limit of the ballistic helmet nanocomposite was as high as 632 m s-1. The developed laminates made of aramid fabric impregnated with poly(BA-a-co-PU) 80/20 containing 0.25 wt% MWCNTs showed great promise for use as a light weight and high-performance ballistic helmet.
ABSTRACT
Objective To establish a valid human head-neck model and ballistic helmet model, and analyze biomechanical responses of the cervical spine under bullet impacts on ballistic helmet with different weights. Methods A uniformly distributed weight of 2 kg was applied on the helmet (1.24 kg), and bullet impacts from frontal, lateral and crown directions at the speed of 450 m/s were considered to obtain the mechanical response of human vertebrae. Results The stress of the cervical spine was significantly higher than that of the skull under bullet impacts, and the stress of C3 segment was the largest, indicating that the cervical spine was more vulnerable than the head during bullet impacts under the protection of ballistic helmet. When the weight of helmet attachment was not considered, the maximum stress of the cervical spine under lateral impact was 2.58% higher than that under frontal and crown impacts. The frontal impact led to the greatest damage to the head, with an increase of 59.4% in head stress. When the weight of helmet attachment was considered, a lager helmet weight would cause a more serious spine injure. When the helmet weight was increased from 1.24 kg to 3.24 kg, the crown impact led to the greatest damage to the cervical spine, with an increase of 12.98% in cervical stress compared with impacts from other directions. Conclusions Lightweight should be considered in the design of ballistic helmet, and the research findings provide scientific references for the design of ballistic helmet.
ABSTRACT
Objective To establish a valid human head-neck model and ballistic helmet model, and analyze biomechanical responses of the cervical spine under bullet impacts on ballistic helmet with different weights. Methods A uniformly distributed weight of 2 kg was applied on the helmet (1.24 kg), and bullet impacts from frontal, lateral and crown directions at the speed of 450 m/s were considered to obtain the mechanical response of human vertebrae. Results The stress of the cervical spine was significantly higher than that of the skull under bullet impacts, and the stress of C3 segment was the largest, indicating that the cervical spine was more vulnerable than the head during bullet impacts under the protection of ballistic helmet. When the weight of helmet attachment was not considered, the maximum stress of the cervical spine under lateral impact was 2.58% higher than that under frontal and crown impacts. The frontal impact led to the greatest damage to the head, with an increase of 59.4% in head stress. When the weight of helmet attachment was considered, a lager helmet weight would cause a more serious spine injure. When the helmet weight was increased from 1.24 kg to 3.24 kg, the crown impact led to the greatest damage to the cervical spine, with an increase of 12.98% in cervical stress compared with impacts from other directions. Conclusions Lightweight should be considered in the design of ballistic helmet, and the research findings provide scientific references for the design of ballistic helmet.
