The Advanced Crew Escape Suit (ACES) is a pressurized suit worn by astronauts during launch and landing phases of Space Shuttle
operations. In 2008, a large tear (12.7–25.4 mm long, between the pinky and ring finger) in the ACES left-hand glove made
of neoprene latex rubber was found during training for Shuttle flight STS-124. An investigation to help determine the cause(s)
of the glove tear was headed by the NASA Johnson Space Center (JSC) in Houston, Texas. Efforts at JSC to reproduce the actual
glove tear pattern by cutting/tearing or rupturing were unsuccessful. Chemical and material property data from JSC such as
GC-MS, FTIR, DSC, and TGA mostly showed little differences between samples from the torn and control gloves. One possible
cause for the glove tear could be a wedding ring/band worn by an astronaut. Even with a smooth edge, such a ring could scratch
the material and initiate the tear observed in the left-hand glove. A decision was later made by JSC to not allow the wearing
of such a ring during training or actual flight. Another possible cause for the ACES glove tear is crystallinity induced by
strain in the neoprene rubber over a long period of time and use. Neoprene is one among several elastomers known to be susceptible
to crystallization, and such a process is accelerated with exposure of the material to cold temperatures plus strain. When
the temperature is lowered below room temperature, researchers have shown that neoprene crystallization may be maintained
at temperatures as high as 7.2–10 °C, with a maximum crystallization rate near −6.7 to −3.9 °C (Kell et al. J Appl Polym Sci
2(4):8–13, 1959 [<cite>1</cite>]). A convenient conditioning temperature for inducing neoprene crystallization is a typical freezer that is held near −17.8
°C. For work at the NASA Marshall Space Flight Center (MSFC), samples were cut from several areas/locations (pinky/ring finger
crotch, index finger and palm) on each of two pairs of unstrained ACES gloves for DSC and DMA thermal analysis testing. The
samples were conditioned in a freezer for various times up to about 14 days. Some rectangular conditioned samples were unstrained,
while most were subjected to strains up to 250% with the aid of two slotted aluminum blocks and two aluminum clamps per sample.
Trends were observed to correlate DSC data (heat of fusion) and DMA data (linear CTE and stress for iso-strain testing) with
(a) sample location on each glove; and (b) percent strain during conditioning. Control samples cut “as is” from each glove
location were also tested by DSC and DMA.
Authors:W. Menendez Sanchez, B. Zwicker, and A. Chatt
A combination of solid phase extraction, coprecipitation, and neutron activation techniques has been used to develop a speciation
analysis method based on green chemistry for the major arsenic species in drinking water. Arsenate as As(V), monomethylarsonic
acid (MMA), and dimethylarsinic acid (DMA) are separated and preconcentrated by strongly anion and cation exchange columns
in tandem while As(III) remains in the effluent. These species are then selectively eluted and As(III) coprecipitated with
bismuth sulphide. This simple method has been applied to the analysis of water reference materials with good results. The
detection limits are 0.9, 1.7, 1.6, 3.8 and 16 ng mL−1 for As(III), As(V), MMA, DMA and total arsenic, respectively, using a neutron flux of 2.5 × 1011 cm−2 s−1 at the Dalhousie University SLOWPOKE-2 reactor (DUSR) facility and anti-coincidence gamma-ray spectrometry.
Authors:E. Martínez-Flores, Jesús Negrete, and Gabriel Torres-Villaseñor
A study of loss modulus values was conducted for three different metal alloys, in both superplastic and non-superplastic condition,
using Dynamic Mechanical Analysis (DMA). Results showed a direct relationship between loss modulus values and the homologous
superplastic temperature for each of the three different metal alloys that were studied.
Thermomechanical properties of bread components can be used to characterize various events that have direct rheological impacts. The objective is to observe changes that occur during staling and toughening of a bread or similar products. In this article, characterization of bread polymers, starch and gluten, were examined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA).
Authors:N. Delpouve, C. Lixon, A. Saiter, E. Dargent, and J. Grenet
Temperature modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA) are used to calculate
cooperative rearranging region (CRR) average sizes for drawn poly(ethylene terephthalate) (PET) with different draw ratios
(λ) ranging from λ=1 to 4, according to Donth’s approach. It is shown for both studies that the CRR size decreases when increases,
due to the amorphous phase confinement by the crystals generated during the drawing. However, differences observed between
the values calculated from TMDSC and DMA investigations are explained by the differences between a mechanical uniaxial dynamic
solicitation (DMA) or a thermal solicitation (TMDSC) in terms of cooperative rearrangements at the glass transition.
Differential scanning calorimetry (DSC) was used to indicate the relative extents of the different cure reactions of the 4-glycityloxyl-N,
N-diglycidylaniline (MY0510), polyglycidyl ether of phenol formaldehyde novolac (DEN431) and 3,3 diamino diphenylsulphone
(3,3 DDS) resin systems and how these were affected by the presence of polyethersulphone (PES). The extent of reactions at
any given time decreased with increasing PES concentration and the reaction rate maximum shifted to longer times. The cured
resin systems were examined using dynamic mechanical analysis (DMA). Broader β-transitions of lower intensities were observed
in specimens containing PES, suggesting an increased range of relaxations within the transition.
In dealing with phenomena which show a linear response such as viscoelastic or dielectric properties, measurements are carried
out by observing the relationship between the stimulus applied to the sample and the response from the sample. Since the Fourier
analysis technique is effective in obtaining this relationship, two types of circuitries based on Fourier analysis have been
created. Both DMA and dielectric measurement were used to evaluate these circuitries. Results were satisfactory, especially
with respect to tanδ precision.
The mechanical properties of solid rocket propellants are very important for good functioning of rocket motors. During use
and storage the mechanical properties of rocket propellants are changing, due to chemical and mechanical influences such as
thermal reactions, oxidation reactions or vibrations. These influences can result in malfunctioning, leading to an unwanted
explosion of the rocket motor. Most of modern rocket propellants consist of a polymer matrix (i.e. HTPB) filled with a crystalline
material (i.e. AP, AN). However, the more conventional double base propellants consist of a solid gel matrix with additives,
such as stabilizers. Both materials show a mechanical behaviour, quite similar to that of general polymers. To describe the
material behaviour of both propellants a linear visco-elastic theory is often used to describe the mechanical behaviour for
small deformations. Because the time-temperature dependency is also valid for these materials a mastercurve can be constituted.
With this mastercurve the response properties (stiffness) under extreme conditions can be determined. At TNO-PML a mastercurve
of a double base propellant was constituted using dynamical mechanical analysis (DMA) and compared with a mastercurve reduced
from conventional (static) stress relaxation tests. The mechanical properties of this double base propellant determined by
DMA were compared with conventional (quasi-static) tensile test results.
Authors:Ph. Ponteins, B. Medda, Ph. Demont, and C. Lacabanne
The correlation between structure/microstructure and thermomechanical properties has been investigated by the Thermally Stimulated Creep (TSC) technique in a high performance thermostable thermoset matrix composite. The high resolving power of this technique allows us to analyse the α retardation mode. The kinetics of molecular movements liberated at the glass transition has been investigated by the technique of fractional loading: the analysis of each elementary process gives the real compliance and the retardation time as a function of temperature. The values of the activation parameters show the existence of a compensation phenomenon which characterizes the microstructure. It also gives access to the loss compliance of the composite material as a function of temperature and frequency. The predictive calculation of loss compliance has been validated by the results obtained by dynamic mechanical analysis (DMA).
Authors:L. Barral, J. Cano, A. López, J. López, P. Nogueira, and C. Ramírez
Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of
bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal
degradation indicated a shift of the glass transition temperature (Tg) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time.
The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued
that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the
epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network.