Thermography image

The climatic conditions, air temperature and humidity can all affect the thermal properties of a garment [131]. In a dry environment condition (23 °C and 50% RH) without radiant heat, the vest will exhibit low heat loss due to its thickness and thermal insulation. Figure ‎8.16 (A & B) shows the thermal images using the IR camera for the nude manikin during the thermal insulation and evaporative resistance tests, respectively. The thermography images were captured for the front of both the D1 and D2 vests. Throughout the experiment duration of 1 hour and 40 minutes, the skin temperature was maintained at 35±0.2 °C by the manikin system to simulate the human body. The reason for measuring the front of the vest only was to measure the temperature change effect on dissimilar designs in order to evaluate which design performed better for thermal comfort.

0 0.1 0.2 0.3 0.4 0.5 Uniform 1L 3L 5L Pe rme ab ility in de x (Im) Loose–vest

Shoulders Chest Stomach Back

0 0.1 0.2 0.3 0.4 0.5 1L 3L 5L Pe rme ab ility in de x (Im) Bra–vest

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Figure ‎8.16 IR images for nude manikin

Figure ‎8.17 (A & B) and Figure ‎8.18 (A & B) illustrate the 5-layered D1 and D2 vests dressed on the nude manikin at the start of the test and at the end, respectively. Average temperatures of the right breast (A), left breast (B) and stomach zones (C) were measured at the start and end of the test. Table ‎8.4 shows the surface temperature range for selected zones. It can be seen that the temperature increased for D1 up to 0.9 °C from 27.5 °C to 28.4 °C in zone A and from 25.9 °C to 26.8 °C in zone C and up to 1.7 °C in zone B (from 27.5 °C to 28.9 °C). For the D2 vest zones, the surface temperature had minor increases up to 0.5 °C from 28.4 °C to 28.9 °C and 26.3 °C to 26.8 °C in zones (B and C), respectively, and up to 0.1 °C in zone A (28.3 °C to 28.4 °C) compared with D1. The increase of temperature in both D1 and D2 is attributed to the lower atmospheric temperature of 23 °C compared with the skin temperature of 35 °C. Therefore, the environment cooled the outer layer of the vest. Matusiak [63] indicated that heat exchange between the body and the ambient condition is an important fact that influences garment insulation. Consequently, a lower ambient temperature outside a person’s body causes condensation under single or multi-layered protective clothing [63, 121]. This is shown through the temperature range of the thermotherapy imaging in Figure ‎8.17 and Figure ‎8.18. It can be seen that the thermal insulation of the vest material was influenced by the atmospheric conditions. A further indication is that within the testing time, the D1 vest became warmer than the D2 vest due to being a tight-fitted vest. The D1 vest is fitted loosely in the bust area (A & B) and there is an air gap between the manikin body and the vest; hence the air gap acts as an insulator and therefore the temperature is higher than for D2. The D2 vest is a close fitting garment

(A) Thermal insulation

A B C Environment (B)‎Evaporative resistance A B C Environment

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and there is very little air gap between the busts zones (A & B) and thus less insulation. This is clearly shown by the temperature differences in comparing D1 and D2 (Table ‎8.4).

Table ‎8.4 Temperature range of front vest zones

Figure ‎8.17 IR images for 5L D1 in thermal insulation test

Vest Zone Dry (°C) Wet (°C)

Initial Final Difference Initial Final Difference

D1 A 27.5 ±0.7 28.4 ±0.7 +0.9 36.8 ±0.1 35.3 ±0.9 ˗1.5 B 27.2 ±0.5 28.9 ±0.5 +1.7 36.7 ±0.2 34.6 ±0.5 ˗2.1 C 25.9 ±0.3 26.8 ±0.2 +0.9 37.3 ±0.1 35.8 ±0.2 ˗1.5 D2 A 28.3 ±1.0 28.4 ±0.9 +0.1 37.0 ±0.5 34.7 ±0.9 ˗2.3 B 28.4 ±0.9 28.9 ±0.8 +0.5 35.3 ±0.9 33.7 ±1.2 ˗1.6 C 26.3 ±0.4 26.8 ±0.7 +0.5 37.4 ±0.5 36.1 ±0.8 ˗1.3 (A) Initial A B C (B) Final A B C

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Figure ‎8.18 IR images for 5L D2 in thermal insulation test

The IR images as seen in Figure ‎8.19 and Figure ‎8.20 show minor decreases in the surface temperature of both vests. It can be seen from Table ‎8.4 that the D1 vest surface temperatures decreased by 1.5 °C in zones A and C and by 2.1 °C in zone B. For the D2 vest, temperatures dropped by 2.3 °C, 1.6 °C and 1.3 °C in bust A, B and C, respectively. The decreased temperature of the D1 and D2 vests is attributed to the moisture absorption which is clearly shown in Figure ‎8.19 on the vest sides, and on the centre of the vest in Figure ‎8.20. In addition, the D1 vest has a large gap between the bust zones, so the fabric is not touching the skin in the centre and the air gap increases the insulation; therefore, less moisture is absorbed by the inner fabric. In contrast, the D2 vest is fitted more closely with smaller gaps in the bust zones; hence the wool fabric can absorb more moisture, causing a lower temperature.

(A) Initial A B C (B) Final A B C

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Figure ‎8.19 IR images for 5L D1 in evaporative resistance test

Figure ‎8.20 IR images for 5L D2 in evaporative resistance test

Conclusion 8.5.

The weft-knit single-jersey fabrics, NKA, CNK and NKW, were evaluated for thermal comfort and moisture management performance. The results reveal that NKW has improved moisture management properties compared with NKA. Plating wool into the knitted fabric produces good moisture absorbency and transport properties. The knitted fabric NKA has the lowest thermal resistance among all fabrics and NKW shows the highest. After coating, the CNK fabric’s Rct increased slightly but was still less than for NKW. The coating of CNK presented an increase in Ret value compared to

(A) Initial A B C (B) Final A B C (A) Initial A B C (B) Final A B C

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NKA. The study of multi-layered ensembles reveals gradual rises in both Rct and Ret when the layer number is increased.

The 3D knit female body armour vests were also investigated for thermal comfort using a thermal manikin. The loose-vest thermal insulation was higher than for the bra-vest. There was also a significant increase in Rct when the layer number increased. However, the evaporative resistance results show dissimilarities in the chest, stomach, shoulder and back zones. The chest and stomach represent higher results in both Rct and Ret compared to the shoulders and back. The differences in the results have also been revealed by the IR thermography images. The surface temperature of D1 and D2 increased in the thermal insulation test and decreased in the evaporative test. The 5L vests results indicate that the loose-vest is more comfortable than the bra-vest due to the low surface temperature in the bust and stomach zones and evaporative resistance.

Overall, increasing the layer number makes the body armour more uncomfortable to wear. However, this is a compromised result when it comes to protection and comfort, because comfort is not as important as protection. The results show that the five-layer assembly with no coating is better than five layers with one coated layer in terms of both thermal and evaporative resistance. However, the 5L with one coated layer performed better in terms of protection against a single-blade knife.

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Conclusion and Future Research