Transcript Stress Analysis of a Hydraulic Actuator Based on.+

STRESS ANALYSIS OF A
HYDRAULIC ACTUATOR BASED ON
ACCUMULATOR RESPONSE
By John Connor
Ernesto Gutierrez-Miravete, Thesis Adviser
INTRODUCTION
Pressure transients are the primary loads in
hydraulic systems and can be due to several
types of loading conditions which are not
typically seen in normal operation
 This project builds upon Analysis of Accumulator
Response to an External Force acting on a
Hydraulic Actuator by Leonid Simkin
 The analysis determines if that accumulator is
justified based on the reduction of space and
weight the hydraulic actuator needs to be to meet
the design criteria

DESIGN CRITERIA

Stresses were evaluated against established
criteria in the American Society of Mechanical
Engineers (ASME) Boiler Pressure Vessel Code
(BPVC)
1.5 factor of safety on material yield strength
 3.5 factor of safety on material ultimate strength

Material
Yield Strength,
Ultimate Strength,
Unit Weight,
MPa
MPa
kN/m3
169
324
26.6
2011 T6 Aluminum
Alloy
Material
2011 T6 Aluminum
Alloy
Yield Allowable
Ultimate Allowable
Stress, MPa
Stress, MPa
112.7
92.6
Source
[3]
TRADITIONAL APPROACH – CYLINDER
WALL

The analysis assumes a thick-walled cylinder

Circumferential (Tangential) Stress
𝜎𝜃𝜃
𝑝1 𝑎2 − 𝑝2 𝑏2 𝑎2 𝑏2 𝑝1 − 𝑝2
=
+ 2 2
𝑏2 − 𝑎2
𝑎 𝑏 − 𝑎2
a

Axial Stress
𝜎𝑧𝑧

b
p1
Radial Stress
𝜎𝑟𝑟
o
𝑝1 𝑎2 − 𝑝2 𝑏2
𝑃
=
−
𝑏2 − 𝑎2
𝜋 𝑏2 − 𝑎2
𝑝1 𝑎2 − 𝑝2 𝑏2 𝑎2 𝑏2 𝑝1 − 𝑝2
=
− 2 2
𝑏2 − 𝑎2
𝑎 𝑏 − 𝑎2
Von Mises Stress Criteria
𝜎𝑣𝑜𝑛 =
1
[ 𝜎 − 𝜎𝑟𝑟
2 𝜃𝜃
2
+ 𝜎𝑟𝑟 − 𝜎𝑧𝑧
2
+ 𝜎𝑧𝑧 − 𝜎𝜃𝜃 2 ]
p2
TRADITIONAL APPROACH – CYLINDER END
CAP

The analysis assumes a simply supported plate with a
fixed inner diameter (Case 2D)
Bending Moment per unit Length
𝑀 = 𝐾𝑀 𝑞𝑎2
 Maximum Bending Stress
6𝑀
𝜎𝐵 = 2
𝑡

ro
p1
b
b
p2
ro
tEC
FINITE ELEMENT ANALYSIS
Abaqus/Standard was used
to create a static model
using peak pressures
 Half of the actuator was
modeled using symmetry
boundary conditions
 Two Element types were
evaluated

Linear (C3D8I)
 Quadratic (C3D20)


Internal and external
pressures were applied to
the model
RESULTS - STRESS
Actuator Stresses without an Accumulator
Analysis Type
Actuator Area
Thickness (mm)
Stress (MPa)
Traditional
Cylinder Body
9.95
92.3
Analysis
End Cap
7.20
92.4
Abaqus Analysis
Cylinder Body
10.85
92.5
End Cap
11.75
91.4
Actuator Stresses with an Accumulator
Analysis Type
Actuator Area
Thickness (mm)
Stress (MPa)
Traditional
Cylinder Body
7.05
92.3
Analysis
End Cap
6.25
91.6
Cylinder Body
7.65
88.9
End Cap
7.65
92.6
Abaqus Analysis
RESULTS – ABAQUS STRESS PLOTS
Actuator Stresses without an Accumulator
Traditional Approach
Dimensions
Abaqus Optimized
Dimensions
RESULTS – ABAQUS STRESS PLOTS
Actuator Stresses with an Accumulator
Traditional Approach
Dimensions
Abaqus Optimized
Dimensions
COMPARISON BETWEEN DESIGNS

The comparison is based off the Abaqus results
Design
Considerations
Outer
Diameter [m]
Actuator
Weight [N]
No
With
Percent
Accumulator
Accumulator
Difference
0.1667
0.1603
3.8%
428
295
31%
CONCLUSION
Traditional approach did not capture the peak
stresses in the cylinder particularly around the
end cap.
 Abaqus model generated high stresses requiring
optimization of the actuators
 Accumulator addition into this system is not
justified. Since the space envelope and weight of
the actuator did not reduce to a point to justify
the weight of the accumulator.
