Influence of preliminary thermal aging on the residual interlayer strength and staging of damage accumulation in structural carbon plastic

Aging of composites is a pervasive problem that leads to mechanical properties degradation, reduced design life of a structure and premature accidental failure. The work is devoted to an experimental study of the preliminary temperature aging effect on the residual mechanical properties of structural CFRP. The joint use of test systems and systems for registration and analysis of acoustic emission signals was applied. The Short Beam Shear Test of CFRP specimens were carried out using the short beam method. The tests were carried out on universal electromechanical systems Instron 5882 and Instron 5965 in accordance with the recommendations of ASTM D2344. In the process of loading the samples were continuously recorded by using the acoustic emission signals system AMSY-6. A piezoelectric sensor with a frequency range of 300-800 kHz was used. The test and diagnostic systems were synchronized during the tests. In the course of the work the values of the interlayer shear strength were determined for the samples of CFRP. Typical types of the sample destruction are illustrated. When analyzing the change in the mechanical properties of the carbon fiber reinforced plastic from a temperature increase the critical values of temperatures were established in which a sharp decline in the strength and elastic characteristics of materials occurs due to an active destruction of the binder. The graphs of the energy parameter dependence and frequency characteristics of acoustic emission signals on time have been constructed and analyzed. The estimate of the processes of damage accumulation in composites is carried out. The change of the damage accumulation mechanisms was illustrated. The obtained results illustrate the effect of elevated temperatures and the duration of their impact on the mechanical behavior of structural CFRP specimens during the static tests for the interlayer shear.

A 3D RANGE MODULATOR FOR ULTRA-SHORT PROTON FLASH IRRADIATION

Background and aims In the pursuit of optimal parameters for FLASH irradiation, all components involved in the beam delivery should be compatible with requirements spread in an extreme and wide unexplored regime. Aiming for minimal total irradiation times with modulated proton beams, which deliver a flat depth-dose distribution along tumors, a static range modulator has been developed to accommodate ultra-short beam durations regardless of their time structure. The design goals were set to match the functionality of the rotating wheel used for in-vivo and in-vitro FLASH investigations at HZB. Methods Having the form of a ridge filter extended to an additional dimension, a hexagonal-pyramid pattern was configured to an incoming beam of 23 MeV energy with > 1 mm radius, in order to create a 6 mm uniform field with a flat dose range of 5 mm at the target. The manufacturing was done with a 3D printer using VeroWhite, a material similar to PMMA. The lateral and distal dose distribution of both modulators were measured using a Markus Chamber (PTW-Freiburg, Germany) in a water phantom and a radioluminescent screen mounted in front of CCD camera, respectively. Results The developed modulator created very flat dose distributions as designed, with negligible differences to the reference rotating wheel. The positioning tolerances were evaluated as relatively relaxed, with offsets of 2 cm and an angle of 5 degrees not compromising the desired performance. Conclusions The developed static modulator allows systematic proton FLASH studies on small organs using a broad range of timing schemes, disentangled from temporal and spatial incoherencies.

Short beam shear damage analysis of GLARE laminates based on digital image correlation and finite element analysis

The short beam shear performance of GLARE 3A-3/2 laminates with adhesive layers was investigated by combining the short beam test and the digital image correlation technique. The failure behavior was further analyzed based on finite element simulation and micro failure morphology. The results show an 8% and 58% difference in the short beam strength and bending displacement at failure of laminates along two orthogonal directions; The damage behavior of laminates is determined by the bottom unidirectional glass fiber reinforced plastic (GFRP) layers. The two typical failure modes are matrix and fiber fracture in the GFRP layer caused by local bending deformation, and interlaminar delamination between GFRP layers; The distribution of surface strain [Formula: see text] indicates the damage initiation and evolution process. The simulation result of the finite element model established in ABAQUS/Explicit shows consistency with digital image correlation analysis, which provides an effective method to predict the damage behavior of specimens with different ply structures.

The Effect of Thermal Cycling on the Tensile and Shear Behaviors of the Carbon Nanotube-Reinforced Epoxy

The aim of this research is to study the tensile and shear properties and mechanical behavior of carbon nanotube- (CNT-) reinforced epoxy after the resulting composites have been exposed to different thermal cycling environments. Single-walled carbon nanotubes (SWCNTs) are cylindrical molecules that consist of rolled-up sheet of single-layer carbon atoms (graphene) with a diameter of less than 1 nanometer (nm). Thermal cycling environments can exist in many conditions, such as in-earth orbit for satellites which rotate around the earth and pass through the sun illumination and earth’s shadow, and for airplanes which fly in different altitudes with different temperatures. Carbon nanotube-reinforced epoxy is one of the nanocomposite materials which have been broadly used in many applications such as aerospace, automotive, electronics, and other industries. The goal of this study is to fabricate this nanocomposite with different multiwall and single-wall CNT concentrations and expose it to different thermal cycle numbers and determine the changes in tensile and shear properties and failure characteristics. For this purpose, tension and short-beam tests have been used in this research. The addition of multiwall CNT produces better mechanical properties compared to the use of SWCNT reinforcement. However, unreinforced epoxy showed the highest mechanical properties.

NANOENGINEERED GLASS FIBER REINFORCED COMPOSITE LAMINATES WITH INTEGRATED MULTIFUNCTIONALITY

Combining one or more functional capabilities of subsystems within a structure can provide system-level savings, particularly for weight-critical applications such as air and space vehicles. Nanoengineering presents a significant opportunity for additional functionalities on the nanoscale without the necessity to modify shape, design, or load carrying capacity of the structure. Here, an integrated-multifunctional nano-engineered system was preliminarily studied in composite laminate structures. The study would support the exploration of a system designed to serve independent yet synergistic functionalities in life-cycle enhancements, energy savings during manufacturing, in-situ cure (manufacturing) monitoring, and in-service damage sensing. For the preliminary study, an integrated multifunctional composite (IMC) laminate was created via aligned nanofiber introduction into the composite interlaminar region and the laminate surfaces of Hexcel E-glass/913 unidirectional glass fiber prepreg. Various heights ranging from 10 - 40 μm-tall vertically aligned carbon nanotube (VA-CNT) arrays, as well as patterned and buckled VA-CNT architectures, were used to reinforce the weak interlaminar regions within the laminates showing a ~ 4 - 5% increase in short beam strength of VA-CNT reinforced specimens hence demonstrating interlaminar enhancement for life-cycle advancements. The same layers, being electrically conductive, can provide several additional multifunctionalities.

Influence of preheating on the fracture behavior of over-molded short/continuous fiber reinforced polypropylene composites

Over-molded composites (consist of short and continuous fiber composites) have been extensively used in automotive structures because of their lightweight, high strength-to-weight ratio, and ability to make complex profiles. However, the poor interfacial bonding between short and continuous fiber composites reduces the performance of the over-molded composites. The preheating process has been utilized to enhance the interface bond of the over-molded composites. In the present study, the influence of preheating on the fracture behavior was studied by conducting tensile, flexural, short beam shear, mode I and mode II interlaminar fracture tests on over-molded short/continuous fiber polypropylene composites. The experimental results of the preheated specimens demonstrated an enhancement of tensile, flexural and short beam shear strength by 15%, 221% and 17%, respectively, compared with non-preheated specimens. Further, preheating enhanced the mode I and mode II interlaminar propagation fracture toughness by 655% and 44%, respectively compared with non-preheated specimens.