This article informs the essence of major work done by a number of researchers on the analysis of two-step curing mechanism of diglycidyl ether of bisphenol A (DGEBA) epoxy resin in presence of amine curing agents using near- and mid-IR technology. Various peaks used as a marker for resin formation are discussed and their implementation is comprehensively studied. In addition to this, a wide range of information about the importance of reference peaks in both near-IR (NIR) and mid-IR (MIR) regions are congregated and their accuracy is audited. Also discrepancies observed by researchers in epoxy conversion (α) in NIR and MIR regions are reviewed to highlight the comparative advantages of both regions, one over the other. Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 314-321, DOI:http://dx.doi.org/10.14429/dsj.64.7326

http://publications.drdo.gov.in/ojs/index.php/dsj/article/download/7326/4035

Quantitative Analysis of Curing Mechanisms of Epoxy Resin by Mid- and Near- Fourier Transform Infra Red Spectroscopy

A stereology study of fracture surfaces of 1 to 10 wt. % short milled carbon fibre (SMCF) reinforced epoxy was carried out. Single edge notch bending (SENB) sharp crack samples over a fracture length of 10 mm, covering over 90 % fast crack growth, show that fibre – to – fibre distance significantly decreases with increased SMCF content. For 1% SMCF, the mean free path between fibres is 600 μm, whereas for 10 % SMCF, the mean free path is 110 μm, based on over 200 SEM images for each composition. In SENB sharp crack specimens tested at 2.8 mm/min, the slow crack growth region (length nearly zero for neat epoxy and maximum 1.14 mm for 10% SMCF-epoxy composite) shows intensive debonding and pull-out mechanisms. Fracture toughness (KIC) increased from 0.78 MPam1/2 for neat epoxy to 2.71 MPam1/2 for 10 weight % SMCF/epoxy composites thanks to the combined effect of fibre stereology and the debonding/pull-out mechanisms. Notably, the flexural modulus of the 10 wt. % SMCF reinforced epoxy was 58 % higher than that of the neat epoxy.

Improved fracture toughened epoxy matrix system reinforced with recycled milled carbon fibre

This work presents a comprehensive study on the effects of the Friction-based Injection Clinching Joining (F-ICJ) process on the microstructure and local properties of the stake head. The manuscript evaluates the consequences on the quasi-static mechanical performance of hybrid joints of amorphous polyetherimide (PEI) with aluminium AA6082. Through an overlay of microhardness map on a cross-polarized transmitted-light optical microscopy (CP-TLOM) image, two lower-strength microstructural zones in the PEI stake head were observed: a plastically-deformed zone (PDZ) and a thermo-mechanically-affected zone (PTMAZ). When compared to the base material, PDZ and PTMAZ have a reduction of 12%–16% and 8%–12%, respectively, in local mechanical properties. The reduced local strength was associated with distinct volumes of loosely packed PEI chains with unsteady chain conformation and thus larger free volume in the affected regions. The mechanical strength reduction is reversible through physical aging by thermal annealing the joints, which additionally shows that process-induced thermomechanical degradation of PEI by chain scission, as evidenced by size exclusion chromatography (SEC) analysis, does not appear to affect local mechanical strength. An evaluation of typical loading regimes of staked joints in lap shear (average ultimate force of 1419 ± 43 N) and cross tensile (average ultimate force of 430 ± 44 N) testing indicates that the process-induced changes of PEI do not compromise the global mechanical performance of such a structure. These findings provide a better understanding of the relationships between processing, microstructure, and properties for further F-ICJ process optimization.

https://www.mdpi.com/1996-1944/13/5/1027/pdf

Process-related Changes in Polyetherimide Joined by Friction-based Injection Clinching Joining (F-ICJ)

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstration of a 1.5U laser communications terminal for an intersatellite link. The terminal is deployed on a pair of 3U CubeSats in Low Earth Orbit (LEO). The pointing, acquisition, and tracking (PAT) approach includes both coarse and fine systems. The coarse tracking system uses a beacon laser transmitter and receiver camera. The fine tracking system uses a fast steering mirror and quadrant photodiode. The communications transmit and receive paths include a refractive telescope, transmit laser collimator, and avalanche photodetector (APD) receiver. The communications laser full-width, half maximum (FWHM) beam divergence angle is 14.6 arcseconds, and the beacon laser FWHM divergence is 0.75◦ (2700 arcseconds). The opto-mechanical design process includes prediction & verification of assembly alignment & calibration, thermoelastic effects, structural modes & static loading, and fastener analysis. The opto-mechanical assembly has the sensors and laser transmitters kinematically mounted to enable on-ground calibration to less than 25.4 μm decenter, or 0.1◦ tip/tilt. The thermoelastic alignment error between the payload and bus star tracker is estimated via finite element analysis to be less than 9 arcseconds. The payload optical bench is designed with custom thermal isolation and control to maintain 20 ± 10 ◦C. The thermal modeling of the payload is described in detail. Structural static loading and fastener analyses of the CLICK payload under launch loads of 30 G verify margins of safety are greater than 10 and above the recommended values. Modal analyses predict the first resonant frequency to be 888 Hz, above typical vehicle structural vibration ranges with a factor of safety greater than 3.5.

/pdf/optomechanical-design-and-analysis-for-nanosatellite-laser-3rpjxd9i7r.pdf

Optomechanical Design and Analysis for Nanosatellite Laser Communications

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstrator for a 1.5U intersatellite link laser communications terminal deployed on a pair of 3U CubeSats in Low Earth Orbit (LEO). The narrow transmission full-width half-maximum (FWHM) beamwidth of 14.6 arcseconds coupled with a wider beacon FWHM beamwidth of 0.75 degrees requires precise alignment between and inside both terminals. A two stage pointing, acquisition, and tracking approach is used with a fixed beacon. The coarse pointing stage allocates pointing error to misalignments between the payload aperatures and star tracker aperatures induced by thermoelastic effects. A thermal model, structural model, and statistical analyses are integrated to conclude total thermoelastic induced beacon pointing error with respect to the spacecraft body frame to be less than 9 arcseconds. The fine pointing stage of the approach drives optical mount design with tight tolerances, as well as structural and fastener analysis. Required decentering allowances are as tight as 25.4 μm and 0.1◦ of allowable rotation from the ideal positions. Kinematic mounts with a translational resolution of ± 15 μm and an angular resolution of ±30 arcsec are implemented at the most sensitive mount locations to enable precision calibration of the payload on the ground. Structural static loading and modal analyses of the CLICK payload under launch loads are conducted to show that the spacecraft bus will not deform sufficiently to cause a beacon pointing loss and that payload elements will not fail under launch loads of 30 G. Margins of safety for static loading in each direction and for fasteners with respect to separation, shear, and tension are greater than 10, above the recommended value of 0. The first resonant frequency of the payload is over 800 Hz, greater than the standard minimum of 100 Hz. Thesis Supervisor: Kerri Cahoy, PhD Title: Associate Professor of Aeronautics and Astronautics

Optomechanical design for CubeSat Laser Infrared CrosslinKs

Purpose – The purpose of this paper is to investigate the effectiveness of locking or staking of fasteners with epoxy material systems to prevent loss of preload in aerospace environments.Design/methodology/approach – A quantitative experimental method is adopted to evaluate epoxy material systems for staking of fastener assemblies subjected to varying dynamic and thermal loads. A statistical design of experiments is employed to probe specific design parameters.Findings – Results show that epoxy application can provide satisfactory fastener locking under a variety of service conditions. It is found that: Epon 828 epoxy provides superior fastener locking compared to 3M Scotch‐Weld Epoxy 2216; epoxy application around screw threads is more effective than application around screw head; and abrading the plate surfaces with 180 grit SiC paper is not an effective or useful surface preparation technique.Research limitations/implications – The paper is limited to two commercial epoxy material systems and does not...

M. Swank

Papers

Effectiveness of epoxy staking of fasteners in aerospace applications