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Failure Analysis of T-38 Aircraft Burst Hydraulic Aileron Return Line

机译:T-38飞机爆裂液压副翼返回管路故障分析

摘要

During maintenance troubleshooting for fluctuating hydraulic pressures, a technician found that a right hand aileron return line, on the flight hydraulic side, was ruptured (Fig. 1, 2). This tubing is part of the Hydraulic Flight Control Aileron Return Reducer to Aileron Manifold and is suspected to be original to the T-38 Talon trainer aircraft. Ailerons are small hinged sections on the outboard portion of a wing used to generate rolling motion thereby banking the aircraft. The ailerons work by changing the effective shape of the airfoil of the outer portion of the wing [1]. The drawing, Northrop P/N 3-43033-55 (6/1960), specifies that the line is made from 0.375 inch OD, aluminum 5052-0 tubing with a 0.049 inch wall thickness. WW-T-787 requires the tube shall be seamless and uniform in quality and temper [2]. The test pressure for this line is 3000 psi, and the operational pressure for this line is estimated to be between 45 psi and 1500 psi based on dynamic loading during flight. Examination of the fracture surface found evidence of arrest bands originating on the inner diameter (Fig 3). Ductile dimples are observed on the tube fractures (Fig. 4). The etched cross-section revealed thinning and work-hardening in the burst region (Fig. 5). The wall thickness just outside the work-hardened fracture region measured 0.035". Barlow's Formula: P = 2St/D, where P is burst pressure, S is allowable stress, t is wall thickness and D is the outer diameter of tube. Using the ultimate tensile strength of 28 ksi and a measured wall thickness of 0.035 inches at burst, P = 5.2 ksi (burst pressure). Using the yield of 13 ksi (YS) for aluminum 5052-0, plastic deformation will happen at P = 2.4 ksi suggesting plastic deformation occurred at a proof pressure of 3.0 ksi. Conclusion: The burst resulted from high stress, low-cycle fatigue. Evidence of arrest bands originating on the inner diameter. Fracture is predominately shear dimples, characteristic of high load ductile fractures (Fig 6). Section wall reduction in the burst region. Plastic deformation and thinning of the out-of-specification tube wall likely happened during the initial proof testing years ago. Metallography of tubing away from rupture site confirmed tubing was seamless. Based on the tube microstructure, it is likely that the initial wall thickness was about 30 % thinner than the requirement of 0.049 inches. Fracture initiated on the ID and progressed to the OD (shear lip). The tube is made of the correct material of 5052-0 aluminum as verified using Optical Emission Spectroscopy (Table 2). The tubing hardness tested 77 HV100 (77 HRE). This hardness is slightly above the requirement for 70 HRE maximum for aluminum 5052-0 in AMS 2658C [3].
机译:在维修过程中对液压压力波动进行故障排除时,技术人员发现,在飞行液压侧的右副翼返回管路破裂(图1、2)。该油管是Aileron歧管液压飞行控制Aileron回油减速器的一部分,并且怀疑是T-38 Talon教练机的原始油管。副翼是机翼外侧部分的小铰链部分,用于产生侧倾运动,从而使飞机倾斜。副翼通过改变机翼外部[1]的翼型的有效形状来工作。诺思罗普(Northrop)零件编号3-43033-55(6/1960)的图形指定该管线由外径0.375英寸,铝5052-0铝管制成,壁厚为0.049英寸。 WW-T-787要求管子应无缝且质量和回火均匀[2]。该管路的测试压力为3000 psi,根据飞行过程中的动态负载,该管路的工作压力估计在45 psi至1500 psi之间。对骨折表面进行检查后发现有证据表明,止动带起源于内径(图3)。在管破裂处观察到韧性凹痕(图4)。蚀刻的横截面显示出在破裂区域变薄和加工硬化(图5)。刚硬化的断裂区域外的壁厚为0.035英寸。巴洛公式:P = 2St / D,其中P为爆破压力,S为容许应力,t为壁厚,D为管的外径。极限抗拉强度为28 ksi,破裂时测得的壁厚为0.035英寸,P = 5.2 ksi(爆裂压力)。使用铝5052-0的屈服强度为13 ksi(YS),则在P = 2.4 ksi时会发生塑性变形结论:爆裂是由高应力,低周疲劳引起的,爆裂是由内应力引起的。断裂主要是剪切凹坑,是高载荷韧性断裂的特征(图3)。 6)。爆裂区域的断面壁减小,几年前的初步验证测试中可能发生了塑性变形和不合格的管壁变薄,远离破裂部位的管材金相证实了管材是无缝的。根据管的微观结构,很可能初始壁厚比0.049英寸的要求薄约30%。骨折开始于ID,并发展至OD(剪切唇)。该管由5052-0铝的正确材料制成,该材料已通过光发射光谱法验证(表2)。油管硬度测试为77 HV100(77 HRE)。该硬度略高于AMS 2658C中铝5052-0的最大70 HRE的要求[3]。

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