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고온고습 환경하에서 차량용 CFRP 구조부재의 충격강도평가

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Author(s)
박수철
Issued Date
2016
Abstract
1. 최대 정적 압궤하중은 적층각이 어떤 경우나 흡습 시험편이 무흡습 시험편 보다 약
3 ∼ 7 % 정도 작게 나타났으며, 최대 충격 압궤하중은 흡습 시험편이 무흡습 시험
편보다 약 11 ∼ 20 % 정도 작게 나타났다. 이는 흡습에 의한 강도 저하현상이
충격 압궤 일 때가 정적 압궤시 보다 크게 나타남을 알 수 있었다.
2. 충격압궤의 경우 적층각이 15°일 때 최대 압궤하중이 가장 컷으며 그다음 으로는
0°/90° 가 크게 나타났으나, 정적압궤의 경우는 0°/90° 의 경우가 가장 크게 나타
났는데, 이는 정적의 경우 0°방향의 섬유가 15°방향의 섬유에 비해 축압궤하중에 더
저항력이 크기 때문이라 생각된다. 또한, 압궤된 길이는 적층각도가 15°일 때 가
가장 짧아 승객의 안전을 위한 공간 확보가 가능 하다는 차원에서 적층각도가 15°
인 CFRP 구조부재가 가장 우수한 내 충격성을 갖는 것으로 판단된다.
3. 흡습/무흡습 시험편의 정적 압궤시 흡수에너지는 적층각도가 90°/0° 일 때가 가장 높
았으며 그 다음으로 적층각도가 0°/90°, 15°, 45° 90°순으로 났게 나타났다. 그러나
충격압궤시 흡수에너지는 적층각도가 15°, 일 때가 가장 높았으며 45° 90°, 90°/0°
및 0°/90° 시험편보다 약 40% 이상 높았다.
4. 흡습/무흡습 시험편 모두 적층각에 관계 없이 층간크랙 및 층간크랙의 점진적 진전 과 함께 부재의 외측으로 압궤가 진전 되지만 15°로 적층된 부재에서는 부재의 외 측으로 확장하는 스플라인 형상으로 압궤 되었으며, 45°로 적층된 부재에서는 "ᄃ" 자형 부재가 접힘모드의 형상으로 압궤되었고, 90°로 적층된 부재에서는 횡방향의 기지 파단으로 인한 파쇄모드의 형상으로 압궤되었다. 5. 0°/90°로 적층된 부재에서는 층간 크랙 및 층내 크랙의 점진적인 진전과 함께 부재의 외측으로 확장되지만, "ᄃ"자형 부재는 횡방향 전단과 라미나 묶음의 파단이 조합된 취성파괴 모드의 형상으로 압궤되었으며, 0°로 적층된 라미나 묶음은 층간
- 58
크랙 및 층내 크랙 진전에 의해 부재 외측으로 라미나 굽힘을 발생시키지만 축 방 향에 대하여 90°로 적층된 섬유는 0°로 적층된 라미나 묶음의 라미나 굽힘을 방 해하면서 파단 된다. 즉, 섬유는 굽힘이 존재하나 파단에 가까우며 크랙성장과 라미 나 묶음의 굽힘/파괴가 반복적으로 나타난다.
6. 모든 적층각에서 무흡습 상태에서의 시험편 보다는 흡습상태의 시험편은 탄소강화
섬유와 에폭시 사이의 결합력이 수분에 의해 완화가 되기 때문에 무흡습 상태에서
압궤 시 취성의 성격을 갖는 섬유의 파괴나 파단 보다는 연성의 굽힘과 접힘이 주를
이루면서 무흡습 시험편 보다 안정적으로 압궤되었다.
Alternative Title
Impact Strength Evaluation of CFRP Hat Shaped Sectional Members for Vehicle Materials under the Hygrothermal
Alternative Author(s)
Park, Su cheol
Affiliation
조선대학교 산업기술융합 대학원
Department
산업기술융합대학원 융합자동차공학과
Advisor
양인영
Awarded Date
2017. 2
Table Of Contents
목 차

LIST OF TABLES ⅰ
LIST OF FIGURES ⅱ
LIST OF PHOTOGRAPHS ⅴ
ABSTRACT ⅵ


제 1 장 서 론 1
제 1 절 연구배경 1
제 2 절 연구목적 및 연구방법 5

제 2 장 압궤이론 7
제 1 절 복합 박육부재의 압궤모드 7
제 2 절 복합 박육부재의 압궤이론 13

제 3 장 실험방법 18
제 1 절 시험편 18
제 2 절 열습실험 23
제 3 절 충격실험장치 25
제 4 절 충격압궤실험 27

제 4 장 실험결과 28
제 1 절 CFRP 박육부재의 흡습거동 28
제 2 절 CFRP 박육부재의 축압궤실험 결과 31
2-1. 무흡습 CFRP 박육부재의 정적/충격압궤 특성 31
2-2. 흡습 CFRP 박육부재의 충격압궤 특성 41

제 5 장 실험 결과 및 고찰 46
제 1 절 CFRP 박육부재의 정적/충격 압궤강도 46
제 2 절 흡습/무흡습 CFRP 박육부재의 압궤모드 51

제 6 장 결 론 57

참 고 문 헌 59
















LIST OF TABLES





Table 1 Characteristics and use of the CFRP ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 2
Table 2 Material properties of the CFRP prepreg sheet ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 18
Table 3 Types of CFRP hat-shaped sectional members․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 19
Table 4 Moisture absorption rate of CFRP hat-shaped sectional
members (s tacking angles)․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․ 29
















LIST OF FIGURES




Fig. 1 Composite structures for the Airbus A320 3
Fig. 2 The goal of automobile technology development 4
Fig. 3 Crushing process of continuous fiber-reinforced
composite tubes 8
Fig. 4 Crushing characteristics of transverse shearing
crushing mode 9
Fig. 5 Sketch of crack propagation modes 9
Fig. 6 Crushing characteristics of lamina bending crushing mode 10
Fig. 7 Friction related energy-absorption mechanisms 11
Fig. 8 Crushing characteristics of brittle fracturing
crushing mode 12
Fig. 9 Crushing characteristics of local buckling
crushing mode 12
Fig. 10 Collapse pattern of the composite tube under
axial-compress load 15
Fig. 11 Configuration of CFRP single hat shaped member 20
Fig. 12 Stacking conditions of CFRP single hat shaped member 21
Fig. 13 Curing cycle of CFRP stacking specimen 22
Fig. 14 Impact testing setup for crushing 26
Fig. 15 Diagram of measurement system 27
Fig. 16 Moisture absorption rate according to elapsed time of CFRP
hat-shaped sectional members (stacking angles) 28
Fig. 17 Moisture absorption rate of CFRP hat-shaped sectional
members for variation of stacking angles 29
Fig. 18 Collapse processing and Load-displacement curve of
CFRP single hat shaped member,[+15o/-15o]4(Static) 31

Fig. 19 Collapse processing and Load-displacement curve of
CFRP single hat shaped member, [+45o/-45o]4(Static) 32
Fig. 20 Collapse processing and Load-displacement curve of
CFRP single hat shaped member, [90o]8(Static) 33
Fig. 21 Collapse processing and Load-displacement curve of
CFRP single hat shaped member, [0o/90o]4(Static) 34
Fig. 22 Collapse processing and Load-displacement curve of
CFRP single hat shaped member, [90o/0o]4(Static) 35
Fig. 23 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[+15o/-15o]4 (Dry specimen, Impact) 36
Fig. 24 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[+45o/-45o]4 (Dry specimen, Impact) 37
Fig. 25 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[90o]8 (Dry specimen, Impact) 38
Fig. 26 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[0o/90o]4 (Dry specimen, Impact) 39
Fig. 27 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[90o/0o]4 (Dry specimen, Impact) 40
Fig. 28 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[+15o/-15o]4(wet specimen, Impact) 41
Fig. 29 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[+45o/-45o]4(wet specimen, Impact) 42
Fig. 30 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[90o]8 (wet specimen, Impact) 43
Fig. 31 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[0o/90o]4 (wet specimen, Impact) 44
Fig. 32 Collapse shape and Load-displacement curve of CFRP single
hat shaped member,[90o/0o]4(wet specimen, Impact) 45
Fig. 33 Relationship between maximum collapse load and variation
stacking angles (static experiment) 46
Fig. 34 Relationship between maximum collapse load and variation
stacking angles (impact experiment) 47
Fig. 35 Relationship between mean collapse load and variation
stacking angles (static experiment) 48
Fig. 36 Relationship between mean collapse load and variation
stacking angles (impact experiment) 48
Fig. 37 Relationship between absorbed energy and variation
stacking angles (static experiment) 49
Fig. 38 Relationship between absorbed energy and variation
stacking angles (impact experiment) 49
Fig. 39 Relationship between collapsed length and variation
stacking angles (impact experiment) 50




























LIST OF PHOTOGRAPHS



Photo. 1 The crush zone of Carbon/Epoxy tube with half circle
cross-section 13
Photo. 2 Autoclave 22
Photo. 3 Hot waterbath 25
Photo. 4 Collapsed shape of CFRP hat-shaped sectional members 52
Photo. 5 Collapsed shape of CFRP hat-shaped sectional members
(wet specimen) 54
Photo. 6 Collapsed shape of CFRP hat-shaped sectional members
[+15o/-15o]4 55
Photo. 7 Collapsed shape of CFRP hat-shaped sectional members
[+45o/-45o]4 55
Photo. 8 Collapsed shape of CFRP hat-shaped sectional members
[90o]8 56
Photo. 9 Collapsed shape of CFRP hat-shaped sectional members
[0o/90o]4 56
Photo. 10 Collapsed shape of CFRP hat-shaped sectional members
[90o/0o]4 56













ABSTRACT


Impact Strength Evaluation of CFRP Hat Shaped Sectional Members for Vehicle Materials under the Hygrothermal



Park, Soo-Chul
Advisor : Prof. Yang, In-Young, Ph. D.
Dept. of Automotive Engineering
Graduate School of Industrial Technology


The recent trend in vehicle design is aimed at improving the aims at environment- friendliness and collision safety requirements of the vehicles. For the former, the trend is toward light-weight off vehicles to improve fuel efficiency and reduce tail gas emission due to the heavier restriction on exhaust levels. For the latter, however, the trend is toward higher safety performance, comfort level, high-efficiency and multi-functional programs which all increase the weight demands. Therefore, the light weight of vehicle must be achieved in a status of securing safety of collision.
Carbon Fiber Reinforced Plastics of the advanced composite materials as structure materials for vehicles, has a widely application in lightweight structural materials of air planes, ships and automobiles because of high strength and stiffness.
However, CFRP composite materials have the weakness in hygrothermal environment and shock resistance. Especially, moisture ingress into composite material under hygrothermal environment can change molecule arrangement and chemical properties.
The purpose of this study is to evaluate of the crashworthiness for lightweight impact energy absorbing vehicle members under hygrothermal environment .
Following the above study, conclusions are drawn as below;

1. It is found that the moisture absorption characteristics depend on the stacking sequences in the CFRP hat structural members. For the hygrothermals in CFRP hat structural materials, at approximately 0.45∼0.55% of moisture absorption rate, the most absorption rate appears at the beginning time.
2. Through testing both moisturized-absorption sample and non-moisturized sample, at initial collasping time, the decreasing phenomena appears because of the ductile characteristics of moisture ingress in the brittle CFRP composite materals; however, stable collasping phenomena, i.e. the characterictics of bending made the mean loading and absorbed energy higher.
3. When 150 of CFRP prepreg orientation angle, there are interlaminar cracks, intralaminar cracks and central cracks. In the case of 150orientation angle, Maximum impact collapse load is increased more than 50% others orientation angles through performing of both static and impact collapsing testing.
4. Collapsing properties of CFRP hat-shaped members with 15 degree stacking shows the progress of collapsing along with fiber direction for "ㄷ" shaped member due to brittle fracture with transverse shear and laminar bending. For the members with 45 degree stacking, the similar collapsing mode for 15 degree stacking is achieved. Members with 90 degree stacking is collapsed in crush mode due to basal fracture in transverse direction for "ㄷ" shaped member and flange under hygrothermal environment.
Degree
Master
Publisher
조선대학교 산업기술융합 대학원
Citation
박수철. (2016). 고온고습 환경하에서 차량용 CFRP 구조부재의 충격강도평가
Type
Dissertation
URI
https://oak.chosun.ac.kr/handle/2020.oak/1959
http://chosun.dcollection.net/common/orgView/200000265938
Appears in Collections:
Engineering > Theses(Master)(산업기술창업대학원)
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