고밀도 폴리에틸렌 (HDPE) 배관 모재 그리고 배관 버트 융착부에 대하여 여러 인장-인장 응력 조건하에서 피로 시험을 실시하였다. 두 가지의 시험편을 사용하였다. 원주 노치 파이프 (circumferentially notched pipe (CNP)) 시편 (110 mm ...
고밀도 폴리에틸렌 (HDPE) 배관 모재 그리고 배관 버트 융착부에 대하여 여러 인장-인장 응력 조건하에서 피로 시험을 실시하였다. 두 가지의 시험편을 사용하였다. 원주 노치 파이프 (circumferentially notched pipe (CNP)) 시편 (110 mm SDR 9) 그리고 노치 봉 (cracked round bar (CRB)) 형태의 시편으로 10mm, 25mm 그리고 40mm 직경이 사용되었다. 피로실험은 반복주파수 0.1 Hz, 2.0 Hz, 5.0 Hz, R-비는 0.1, 0.3 그리고 23 ℃, 60 ℃, 80 ℃, 95 ℃에서 실시하였으며, CRB 시료는 전자빔이 (100 kGy, 250 kGy, 500 kGy) 조사된 시료 그리고 조사되지 않은 시료가 사용되었다.
23 ℃, 60 ℃, 80 ℃의 시험 온도하에서 파이프 모재보다 융착부의 피로 수명이 짧음은 나타나고 온도가 증가하면서 파이프 모재와 융착부의 피로수명 차이가 점차적으로 커지는 것이 관찰되었다.
CRB 시험편 직경에 대하여, 응력-반복수 곡선에서는 직경이 감소함에 따라 피로 수명은 서서히 증가하였지만 응력 확대 계수를 사용할 경우 직경 감소가 피로 수명을 증가시키는 상반된 결과가 관찰되었다. 이는 작은 시료 직경이 적을 경우 균열길이에 따른 응력 확대 계수 증가 속도가 큰 지경 시료에 비하여 높은 것과 그리고 보다 제한적인 균열성장길이에 기인하는 것임을 알 수 있었다. 파이프 모재와 융착부에 대하여 파괴 시간과 직경의 상관관계 곡선의 기울기는 모두 유사하다는 것은 두 가지 시편에 대한 직경의 효과가 유사한 것으로 판단된다.
융착된 40 mm 직경의 CRB 그리고 CNP 시편의 피로 파괴 시간이 비슷한 현상에 대하여, 균열길이에 따른 CNP 시료의 응력확대계수가 40 mm 직경의 CRB 시료보다 다소 낮지만 시료 파손을 위해 진전되는 균열의 길이가 CNP가 CRB보다 짧은 관계인 것에 의해 일어나는 현상임을 알 수 있었다.
응력비가 증가함에 따라 파이프 모재와 융착부의 피로 수명이 모두 길어진 것을 알 수 있었고 이는 평균 응력보다 응력 진폭이 더 효과적인 영향을 미치는 것으로서 반복수에 따른 균열전진속도를 저하시키는 것에 기인할 수 있다.
전자빔 (EB) 조사에 따른 영향을 연구하기 위해, 파이프 모재와 버트 융착부 시료에 대한 피로 시험을 23 ℃ 그리고 80 ℃에서 실시하였다. 23 ℃ 그리고 Δ σ = (14.4 MPa ~ 8.1 MPa) 범위에서, 조사치 않는 시편보다100 kGy로 조사된 시편의 피로 수명은 짧지만 9.9 MPa 이하의 응력 범위에서500 kGy로 조사된 시편의 피로 수명은 길다는 것이 관찰되었다. 80 ℃ 조건하에서는 파이프 모재는 23 ℃와 유사한 거동을 나타내었지만, 융착부는 조사하지 않는 시편보다 높은 균열 성장이 관찰되었다. 그 이유는 분명하지 않고 앞으로 추가적으로 연구를 통해 증명이 필요한 부분이다.
고밀도 폴리에틸렌 (HDPE) 배관 모재 그리고 배관 버트 융착부에 대하여 여러 인장-인장 응력 조건하에서 피로 시험을 실시하였다. 두 가지의 시험편을 사용하였다. 원주 노치 파이프 (circumferentially notched pipe (CNP)) 시편 (110 mm SDR 9) 그리고 노치 봉 (cracked round bar (CRB)) 형태의 시편으로 10mm, 25mm 그리고 40mm 직경이 사용되었다. 피로실험은 반복주파수 0.1 Hz, 2.0 Hz, 5.0 Hz, R-비는 0.1, 0.3 그리고 23 ℃, 60 ℃, 80 ℃, 95 ℃에서 실시하였으며, CRB 시료는 전자빔이 (100 kGy, 250 kGy, 500 kGy) 조사된 시료 그리고 조사되지 않은 시료가 사용되었다.
23 ℃, 60 ℃, 80 ℃의 시험 온도하에서 파이프 모재보다 융착부의 피로 수명이 짧음은 나타나고 온도가 증가하면서 파이프 모재와 융착부의 피로수명 차이가 점차적으로 커지는 것이 관찰되었다.
CRB 시험편 직경에 대하여, 응력-반복수 곡선에서는 직경이 감소함에 따라 피로 수명은 서서히 증가하였지만 응력 확대 계수를 사용할 경우 직경 감소가 피로 수명을 증가시키는 상반된 결과가 관찰되었다. 이는 작은 시료 직경이 적을 경우 균열길이에 따른 응력 확대 계수 증가 속도가 큰 지경 시료에 비하여 높은 것과 그리고 보다 제한적인 균열성장길이에 기인하는 것임을 알 수 있었다. 파이프 모재와 융착부에 대하여 파괴 시간과 직경의 상관관계 곡선의 기울기는 모두 유사하다는 것은 두 가지 시편에 대한 직경의 효과가 유사한 것으로 판단된다.
융착된 40 mm 직경의 CRB 그리고 CNP 시편의 피로 파괴 시간이 비슷한 현상에 대하여, 균열길이에 따른 CNP 시료의 응력확대계수가 40 mm 직경의 CRB 시료보다 다소 낮지만 시료 파손을 위해 진전되는 균열의 길이가 CNP가 CRB보다 짧은 관계인 것에 의해 일어나는 현상임을 알 수 있었다.
응력비가 증가함에 따라 파이프 모재와 융착부의 피로 수명이 모두 길어진 것을 알 수 있었고 이는 평균 응력보다 응력 진폭이 더 효과적인 영향을 미치는 것으로서 반복수에 따른 균열전진속도를 저하시키는 것에 기인할 수 있다.
전자빔 (EB) 조사에 따른 영향을 연구하기 위해, 파이프 모재와 버트 융착부 시료에 대한 피로 시험을 23 ℃ 그리고 80 ℃에서 실시하였다. 23 ℃ 그리고 Δ σ = (14.4 MPa ~ 8.1 MPa) 범위에서, 조사치 않는 시편보다100 kGy로 조사된 시편의 피로 수명은 짧지만 9.9 MPa 이하의 응력 범위에서500 kGy로 조사된 시편의 피로 수명은 길다는 것이 관찰되었다. 80 ℃ 조건하에서는 파이프 모재는 23 ℃와 유사한 거동을 나타내었지만, 융착부는 조사하지 않는 시편보다 높은 균열 성장이 관찰되었다. 그 이유는 분명하지 않고 앞으로 추가적으로 연구를 통해 증명이 필요한 부분이다.
The fatigue behavior in butt-fusion (BF) joint of high density polyethylene (HDPE) pipe was studied using cyclic tension-tension stress conditions. In addition, parent PE pipe was also investigated for making comparison with BF joint. Two types of specimens were used. One is a circumferentially notc...
The fatigue behavior in butt-fusion (BF) joint of high density polyethylene (HDPE) pipe was studied using cyclic tension-tension stress conditions. In addition, parent PE pipe was also investigated for making comparison with BF joint. Two types of specimens were used. One is a circumferentially notched pipe (CNP) and the other is cracked round bar (CRB) specimens of different diameters. They were tested at fatigue conditions of different stress range, temperature, frequency and R-ratio. Also, the fatigue behavior of BF joints irradiated with electron beam (EB) was investigated to better understand its effect on BF fatigue behavior.
The fatigue lifetimes of BF joints were shorter than that of parent PE pipes at temperatures of 23 ℃, 60 ℃ and 80 ℃. Also, a larger difference in fatigue lifetime between the pipe and BF joint was observed at higher test temperature. It is supposed that the molecular chain structure in extruded pipes are mainly arranged along the direction of the load, but that in BF joint they are known to be parallel to the direction of the load. Also, the developed new micro-structure in the BF joint was more susceptible at higher temperature than room temperature to bear cyclic load is speculated.
In terms of loading frequency, higher the frequency, shorter was the failure times for BF joint. This was speculated to be due to increasing the test frequency accelerating the slippage of molecular chain and thus speed up the fatigue failure.
With regard to the CRB specimen diameter, the fatigue lifetime gradually increased with decreasing diameter, when plotted using the stress range. However, an opposite behavior was observed when the stress intensity factor used. This can be attributed to, for smaller diameter specimen having higher rate of stress intensity factor increase, in addition to having to travel smaller distance for failure. Since for a given stress range, the stress intensity factor value is larger for the larger diameter specimen and hence the specimen fails earlier, as observed. The slope of the failure times versus the diameter curves in the pipe and BF joint was observed to be similar in a double-logarithmic diagram, indicating that the effect of specimen diameter in both pipe and BF joint is similar.
In addition, a similar behavior was found between the failure times of BF joined 40 mm diameter CRB specimens and CNP specimens. This can be attributed to having a slight larger stress intensity factor value with crack length in 40 mm diameter CRB specimen as compared to the CNP specimen. Since the crack growth distance is assume to be longer for the 40 mm CRB specimen as compared to 110 mm SDR 9 CNP specimen, this slightly larger stress intensity factor for CRB specimen would cause higher rate of crack growth. Thus, making the failure times between these two specimen to be similar.
For different R-ratio fatigue tests, the fatigue lifetime of both pipe and BF joint increases with rising R-ratio was observed. This behavior was attributed to mean stress being less effective than the stress amplitude. Additionally, a previous work was noted which showed the crack growth rate decreasing with increasing R-ratio.
The CRB fatigue tests in EB irradiated pipe and BF joint were performed at two different temperatures, 23 ℃ and 80 ℃. And following general observations were made. For both specimens, at 23C, the fatigue lifetime of 100 kGy EB irradiated samples was shorter in all the stress range (Δ σ = 14.4 MPa to 8.1 MPa) applied. However, the fatigue lifetime behavior of 500 kGy EB irradiated samples were different in that at lower values of stress higher fatigue lifetime was observed. At 80 ℃, while the pipe specimen showed a similar behavior to 23 ℃, the BF joint specimen indicated that 100kGy EB was more resistance to fatigue crack growth than the un-irradiated BF joint. The reason for the above behavior is not clear and this should be investigated further in the future.
The difference in fatigue lifetimes between the pipe and BF joint with EB irradiation was smaller than un-irradiation sepecimen, as was observed at 23 ℃ and 80 ℃ temperatures.
The fatigue behavior in butt-fusion (BF) joint of high density polyethylene (HDPE) pipe was studied using cyclic tension-tension stress conditions. In addition, parent PE pipe was also investigated for making comparison with BF joint. Two types of specimens were used. One is a circumferentially notched pipe (CNP) and the other is cracked round bar (CRB) specimens of different diameters. They were tested at fatigue conditions of different stress range, temperature, frequency and R-ratio. Also, the fatigue behavior of BF joints irradiated with electron beam (EB) was investigated to better understand its effect on BF fatigue behavior.
The fatigue lifetimes of BF joints were shorter than that of parent PE pipes at temperatures of 23 ℃, 60 ℃ and 80 ℃. Also, a larger difference in fatigue lifetime between the pipe and BF joint was observed at higher test temperature. It is supposed that the molecular chain structure in extruded pipes are mainly arranged along the direction of the load, but that in BF joint they are known to be parallel to the direction of the load. Also, the developed new micro-structure in the BF joint was more susceptible at higher temperature than room temperature to bear cyclic load is speculated.
In terms of loading frequency, higher the frequency, shorter was the failure times for BF joint. This was speculated to be due to increasing the test frequency accelerating the slippage of molecular chain and thus speed up the fatigue failure.
With regard to the CRB specimen diameter, the fatigue lifetime gradually increased with decreasing diameter, when plotted using the stress range. However, an opposite behavior was observed when the stress intensity factor used. This can be attributed to, for smaller diameter specimen having higher rate of stress intensity factor increase, in addition to having to travel smaller distance for failure. Since for a given stress range, the stress intensity factor value is larger for the larger diameter specimen and hence the specimen fails earlier, as observed. The slope of the failure times versus the diameter curves in the pipe and BF joint was observed to be similar in a double-logarithmic diagram, indicating that the effect of specimen diameter in both pipe and BF joint is similar.
In addition, a similar behavior was found between the failure times of BF joined 40 mm diameter CRB specimens and CNP specimens. This can be attributed to having a slight larger stress intensity factor value with crack length in 40 mm diameter CRB specimen as compared to the CNP specimen. Since the crack growth distance is assume to be longer for the 40 mm CRB specimen as compared to 110 mm SDR 9 CNP specimen, this slightly larger stress intensity factor for CRB specimen would cause higher rate of crack growth. Thus, making the failure times between these two specimen to be similar.
For different R-ratio fatigue tests, the fatigue lifetime of both pipe and BF joint increases with rising R-ratio was observed. This behavior was attributed to mean stress being less effective than the stress amplitude. Additionally, a previous work was noted which showed the crack growth rate decreasing with increasing R-ratio.
The CRB fatigue tests in EB irradiated pipe and BF joint were performed at two different temperatures, 23 ℃ and 80 ℃. And following general observations were made. For both specimens, at 23C, the fatigue lifetime of 100 kGy EB irradiated samples was shorter in all the stress range (Δ σ = 14.4 MPa to 8.1 MPa) applied. However, the fatigue lifetime behavior of 500 kGy EB irradiated samples were different in that at lower values of stress higher fatigue lifetime was observed. At 80 ℃, while the pipe specimen showed a similar behavior to 23 ℃, the BF joint specimen indicated that 100kGy EB was more resistance to fatigue crack growth than the un-irradiated BF joint. The reason for the above behavior is not clear and this should be investigated further in the future.
The difference in fatigue lifetimes between the pipe and BF joint with EB irradiation was smaller than un-irradiation sepecimen, as was observed at 23 ℃ and 80 ℃ temperatures.
※ AI-Helper는 부적절한 답변을 할 수 있습니다.