ESDU 90018-1990 不同紧固件系统铝合金接头的疲劳性能（高载荷传递）

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90018



FATIGUE OF ALUMINIUM ALLOY JOINTS WITH VARIOUS FASTENER SYSTEMS.

HIGH LOAD TRANSFER

1. INTRODUCTION

This Item presents data on the fatigue endurance, secondary bending and load transfer of high load transfer

joints. Bending as a consequence of joint geometry is termed secondary bending (this term is defined in

Section 3) and is shown to be a factor that has great influence on the fatigue lives of high load transfer

joints. In most situations secondary bending will reduce the fatigue endurance of a joint and this reduction

can be significant when high values of secondary bending ratio apply. Two further factors for which data

are presented are fastener fit and hole preparation. Both of these can have significant effects on the fatigue

endurance of high load transfer joints.

Endurance curves of the total peak stress plotted against endurance (in FALSTAFF* flights) are provided.

These allow estimation of fatigue endurance for high load transfer joints. The total peak stress is the sum

of the peak stress due to the axial load and the peak stress due to the secondary bending in the joint. The

peak axial stress is taken as the net peak stress in the fighter aircraft loading sequence, FALSTAFF. The

stress due to secondary bending is taken to be the product of the peak axial stress and the average secondary

bending ratio.

The data in this Item are derived from tests using proprietary fasteners. These fasteners were fitted according

to standard practice. In all the tests failure occurred in the joint itself; there were no fastener failures.

Data are presented for five joint types in all of which secondary bending occurred under load. For two of

these joint types there is a double shear equivalent joint for which data are also presented. These equivalent

joints are subject to negligible secondary bending and they therefore provide a basis upon which the

influence of secondary bending can be assessed. The data show that while cold expansion of the holes and

the use of interference fit fasteners can give large increases in fatigue endurance, these increases can be

completely negated by high secondary bending.

*Fighter Aircraft Loading STAndard For Fatigue evaluation, see Data Item No. 97018, “Standard fatigue loading sequences”.

Issued September 1990

ESDU product release: 2006-01. For current status, contact ESDU. Observe Copyright.

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90018



2. NOTATION

Both SI and British units are quoted.

3. HIGH LOAD TRANSFER JOINTS

It is convenient to define bolted structural joints as being of low, medium or high load transfer depending

upon the fraction of the load that is transferred between members at the first row of fasteners. Low load

transfer joints are usually defined as those that transfer less than 10 per cent of their load between members.

The fatigue strength of low load transfer joints is the subject of Data Item No. 89046* . Medium load transfer

joints transfer between 10 and 30 per cent of their load between members. The fatigue strength of medium

load transfer joints is the subject of Data Item No. 90009† . Usually, if a joint transfers more than 30 per

cent of its load between members, it is considered to be a high load transfer joint. Many joints in aircraft

wings are either medium or high load transfer joints.

This Item presents the results of strain measurement and fatigue tests on a variety of high load transfer

joints. These joints are illustrated in Sketches 7.1 to 7.5. Apart from the double shear equivalent joints, all

the joints experience secondary bending under the application of an axial load. Under axial loading, a

bending moment is established in the region of the fasteners due to the asymmetric distribution of the load

and this is termed secondary bending. The secondary bending ratio, rsb , is defined as the ratio of the

measured bending strain to the measured direct strain. The secondary bending ratios in these tests were in

the range 0 to 1.55. The methods by which the secondary bending ratio and load transfer were measured

are illustrated in Sketch 7.6. The values of the secondary bending ratio and load transfer are presented as

functions of the applied load. The secondary bending ratio for a particular joint also varies with fastener

type, size and fit, and other factors. The double shear equivalent joints, by virtue of their symmetry, have

been assumed to have negligible secondary bending. For this reason no measurements of their secondary

bending ratios were made.

clearance, dh – dfmin

, fastener and hole diameter, respectively m in

, axial and bending strain, respectively (see Sketch 7.6a)

0.2 per cent proof stress of material N/m2lbf/in2

tensile strength of material N/m2lbf/in2

interference, df – dhmin

secondary bending ratio,

peak (level 32) stress in FALSTAFF sequence based on net

cross-sectional area N/m2lbf/in2

total peak stress N/m2lbf/in2

ST = (1 + rsb) Smax

*Data Item No. 89046 “Fatigue of aluminium alloy joints with various fastener systems. Low load transfer”.

†Data Item No. 90009 “Fatigue of aluminium alloy joints with various fastener systems. Medium load transfer”.

dfdh

εaεb

rsb rsb

εb

εa

-----

Smax

ESDU product release: 2006-01. For current status, contact ESDU. Observe Copyright.

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90018

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The C-type joint (Sketch 7.1) is a single lap joint with three fastener rows and is subject to high secondary

bending. The double shear equivalent of the C-type is the C1-type (Sketch 7.1) which has two splice plates

joining the two main plates. Owing to its symmetry its secondary bending ratio should be negligible. The

1½ Dogbone joint (Sketch 7.2) is intended to simulate the load transfer and secondary bending

characteristics of runouts of stiffeners attached to the skins of aircraft wings. Load transfer in the 1½

Dogbone joint is dependent to a large extent on the fastener system fitted. It also has a low compression

limit load of approximately 10 kN (2200 lbf) beyond which buckling is likely to occur. In the 1½ Dogbone

double shear equivalent (Sketch 7.2) a third plate is used to give symmetry and thus minimise secondary

bending. The Q-joint (Sketch 7.3) is based on a single lap joint but the addition of a third plate reduces

bending by increasing lateral stiffness. Also, the double shear connection at the controlling section helps

ensure that fatigue failure occurs at the test section. The X-joint (Sketch 7.4) comprises a system of three

doubler plates in single shear arranged to provide load transfer and different secondary bending

characteristics from the C-type joint. The U-joint (Sketch 7.5) is a derivative of the X-joint. It is essentially

a single column X-joint with a U-channel splice plate instead of the flat plate used in the X-joint. The

U-joint represents a skin joint at a relatively stiff structural member.

4. TEST DETAILS

4.1 Testing Procedure and Specimen Preparation

All the endurance tests were carried out with the FALSTAFF loading sequence (References 5 and 6). The

quoted values of peak stress are the maximum values of stress in the FALSTAFF sequence (level 32). The

stresses are based on the net cross-sectional area of the particular joint at the first row of fasteners.

The measurements of secondary bending ratio and load transfer were made under static loading. The joints

were subjected to a large number of loading cycles before the measurements were taken, to ensure that the

strain response to load had stabilised. These measurements were made using strain gauges as shown in

Sketch 7.6.

In the majority of the tests, 6.35 mm (0.25 in) diameter fasteners were used. In the controlling section of

the Q-joint (see Sketch 7.3) a 4.76 mm (0.1875 in) diameter fastener was used as the datum. However, in

the tests on the Q-joint with the Hi-lok fastener systems, fasteners of both 6.35 mm (0.25 in) and 4.76 mm

(0.1875 in) diameter were fitted in the controlling section of the joint. The results from these particular tests

are separated in the presentation here according to the size of the Hi-lok fastener fitted in the controlling

section.

All the joints except the C and C1 types were manufactured from 7050-T76. The C and C1 types were

manufactured from 7050-T7651. Data are given for these materials in Table 7.1. The general procedure for

producing the fastener holes was: pilot drill, ream, cold expand, ream, deburr, measure the hole diameter,

and countersink. The cold expansion and second reaming operations were only employed for those fastener

systems with cold expanded holes (see Sections 4.3 and 4.4). The joint plates were treated with epoxy

primer and all the joints except the C and C1 types were assembled with interfay sealant PR1431G. No

sealant was used in the assembly of the C and C1 type joints.

4.2 Introduction to Fastener Systems

The two fastener types for which data are presented are Hi-lok and Hi-tigue and these are illustrated in

Sketch 7.7. These fasteners are used in four fastener systems which are described in this section. The values

of interference or clearance are given in Table 7.2. The countersinks were of included angle 100° and depth

1.52 mm (0.060 in).

ESDU product release: 2006-01. For current status, contact ESDU. Observe Copyright.

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标签： #铝合金 #接头 #合金

摘要：

ESDU 90018-1990 标准规范详细分析了不同紧固件系统在铝合金接头中承受高载荷传递时的疲劳性能。该文档为航空航天、机械制造及结构工程领域的设计人员提供了关键数据支持，对比了铆接、螺栓连接及干涉配合等多种紧固方式对铝合金接头疲劳寿命的影响。通过系统性的实验数据与理论分析，它帮助工程师在高应力循环工况下优化接头设计，预防疲劳失效，从而提升整体结构的可靠性和耐用性。无论是对现有结构进行疲劳评估，还是开发新高强度铝合金连接方案，ESDU 90018-1990 都是一份不可或缺的技术参考。

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ESDU 90018-1990 不同紧固件系统铝合金接头的疲劳性能（高载荷传递）

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