Weathering and Forced Movement Exposure

The outdoor exposure to natural weathering was carried out in two locations in Central Japan, located within Yamanashi Prefecture (near Mount Fuji, west of To­kyo) and in Choshi City (near Narita International Airport, east of Tokyo). At both sites the specimens were exposed for a period of four years on weathering racks with an inclination angle of 30° to the horizontal and facing toward the south.

The test specimens in Yamanashi Prefecture were exposed both statically (i. e., without forced movement) and dynamically (i. e., with forced movement); during the exposure the extension/compression cycles were periodically reversed. Test specimens at the Choshi City site were exposed only dynamically. In an earlier study [6], the effect of the frequency of the extension/compression cycling on the sealants was studied. That study found only a rather small effect of the cycling frequency on the surface degradation of the sealant with the cy­cling frequency being set at seven times in a week, two times in a week, one time in a week, and one time in one month [6]. For historical reasons, the exten­sion and compression position was periodically reversed twice per week at the Yamanashi site and once per month at the Choshi site. Only later was it decided that a reversal of the extension/compression cycle once per month presented the best compromise between the degradation achieved and the work load required for handling the test specimens [6]. Table 3 provides information on the weathering and exposure conditions at both exposure sites.

Accelerated weathering was carried out in automated exposure devices using three artificial light sources: filtered xenon arc, fluorescent ultraviolet lamps, and open flame carbon arc, as standardized in JIS A 1415 [7] (similar to ISO 4892 [8-11]). The following legend is applied throughout this paper in order to expediently identify the different light sources: filtered xenon-arc, XWOM; open-flame carbon arc, SWOM; fluorescent ultraviolet, UV. Exposure to acceler­ated artificial weathering was carried out for a total period of 5000 h, with the

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TABLE 3—Outline of weathering test for outdoor exposure.

Location of Exposure

Term of Exposure

Direction/Angle

Interval of Extension/ Compression Exchange

Position of Evaluation

Set 1 Yamanashi

Jan. 16, 2003,

South/30°

*None

*±0 %

Prefecture

through

(static)

*±1.5%

Jan. 15, 2007

*Twice/week

*±15%

(dynamic)

*±25%

Set 2 Choshi

October 1, 2002,

South/30°

*Once/month

*±1.5%

City

through

(dynamic)

*±15%

September 13, 2006

*±25%

extension and compression position periodically reversed every 500 h (note: the influence of the exchange interval in the accelerated weathering exposure is cur­rently being considered within ISO/TC59/SC8/WG10 [12]).