Stressed temperature/humidity test

One of the earlier methods used by the Army for evaluating the durability of adhesive-bonded joints is the stressed temperature/humidity test described in ASTM D2919-01. Army ARDC workers at Picatiimy Arsenal... 

Tables 2—5 Hst some typical properties or ranges of properties for the more common film and sheet products. Although these values are good for comparative purposes, actual performance tests are best to determine suitabiHty for use. Properties of multiple-layer films or sheets in laminar stmctures cannot always be predicted from values for the individual polymer layers. Use conditions of stress, temperature, humidity, and light exposure all strongly influence performance. Film and sheet manufacturers can recommend product combinations or variations that may provide significant performance advantages to the user.

Iteratively, information is on one hand gathered from stability tests based on exposing the formulation to different physical stresses (temperature, humidity, light over time) and on the other hand information is obtained seqnentiaUy out of in vivo tests. Of particular interest is a consistent response/exposure to the wide range of doses administered from the pharmacological up to the toxicological experiments. 

The degradation of the matrix in a moist environment strongly dominates the material response properties under temperature, humidity, and stress fatigue tests. The intrinsic moisture sensitivity of the epoxy matrices arises directly from the resin chemical structure, such as the presence of hydrophilic polar and hydrogen grouping, as well as from microscopic defects of the network structure, such as heterogeneous crosslinking densities. 

Tensile strength, which is a measure of the ability of a polymer to withstand pulling stresses, is usually measured using a dumbbell-shaped specimen (ASTM D-638-72 Figures 14.11 and 14.12). These test specimens are conditioned under standard conditions of humidity and temperature before testing. 

The test specimens should be stressed in directions that are representative of the forces that the bond will see in service, i.e., shear, peel, tension, or cleavage. If possible, the specimens should be prepared and cured in the same manner as actual production assemblies. If time permits, specimens should also be tested in simulated service environments, e.g., high temperature, humidity. 

The carefully bred strains of animals used for toxicology testing may be much more uniform in their responses, but they are more sensitive to environmental stresses than their wild cousins. Temperature, humidity, and airflow in the animal quarters must be tightly controlled and adjusted to the optimum value for the individual species. Ventilation in the animal rooms should be equivalent to 12 to 15 changes per hour without drafts on the animals. 

Abstract Coupled THM simulation of the FEBEX, which is the full-scale in-situ Engineered Barrier System Experiment performed in Grimsel Test Site in Switzerland, is one Task in the international cooperation project DECOVALEX III. In the Task, the simulation of the thermal, hydraulic and mechanical behaviour in the buffer during heating phase is required, e.g. the evolutions and the distributions of stress, relative humidity and temperature at the specified points in bentonite buffer material. 

This work does not address the fundamental question of mirror corrosion mechanisms. Rather, our study was limited to visual observations of weathering effects upon commercial products exposed to extreme conditions in an environmental test chamber. The principal parameters investigated were 1) the materials ability to protect silvered mirrors from moisture and 2) the effect of mechanical stress (coefficients of expansion mismatches) due to temperature-humidity cycling. 

Stresses are herein defined as conditions that will degrade system performance. For solar systems these stresses can include temperature, humidity, UV radiation, and temperature cycling. Once stresses are identified, then tests are designed to subject the system to each particular stress Independently... 

DMTA (or DMA)—the exciting of a material with a periodic stress and monitoring of the resultant strain—has become a commonly used technique for both scientists and engineers who need to know the viscoelastic properties of a material with respect to temperature, humidity, vibration frequency, dynamic or static strain amplitude, or other parameter against time. This chapter will attempt to introduce its principles, cover a short history of the technique relating it to other mechanical tests, and discuss its application to a wide range of polymers and other materials. 

Crack propagation tests for the 3.18-mm (0.125-in.) material were run in room-temperature humid air at frequencies of 20, 10, and 1 Hz with an R value of 0.1. A few tests were also run for R values of 0.3 and a frequency of 10 Hz to examine any stress ratio effects. Tests on the 5.59-mm (0.22-in.)-thick samples... 

Textile membranes are exposed not only to mechanical stresses but also to various environmental influences. The main damaging influences are temperature, humidity, solar irradiation, noxious industrial gases, ozone, dust, salts and micro-organisms. These influences impair the functional properties, performance and life-span of the membranes. DIN EN ISO 4892 standard describes the basics for these tests. It is expected that textile membranes should last for decades without their properties and performance being compromised. However, every year many materials break down due to severe environmental influences and cause damage worth millions of euros. 

Humidity testing is nearly always carried out at temperatures ranging from 351-100°C with relative humidity from nearly zero to 100 %. Occasionally, steam bombs are used so tests can be run above 100°C. In the last ten years, highly accelerated stress tests have been developed to enable materials to be tested at temperatures above 100°C, but at a noncondensing relative humidity, typically 85 %. The most common applications for these tests are in evaluating coatings, paper, adhesives, adhesion between mechanically or chemically bonded materials, and, in electronics, for evaluating the effectiveness of device encapsulation. 

The components can be tested for SCC to evaluate the effects of applied and residual manufacturing tensile stresses leakage resistance after salt spray or temperature-humidity cycling tests and contact resistance after a salt spray test, temperature-humidity cycling, or a hydrogen sulfide exposure test. 

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