使用ANSYS-LSDYNA模拟SHPB实验中棒材错位影响

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"这篇文档是关于在ANSYS中使用LS-DYNA进行数值模拟研究分体霍普金森压杆（Split Hopkinson Pressure Bar, SHPB）实验中棒材错位效应的专业论文。作者Muhammad A. Kariem和John H. Beynon等人探讨了六种常见的棒材错位类型，包括中性轴偏移、支撑高度不均、非平行冲击面、棒材直线度、穹顶和中心圆孔的不规则等，以及它们如何导致信号畸变。" 在ANSYS中集成的LS-DYNA是一款强大的非线性动力学分析软件，常用于模拟瞬态动态事件，如碰撞、爆炸和材料的动态响应。在SHPB实验中，精确的棒材对准至关重要，因为它直接影响到实验结果的准确性和信噪比。SHPB技术是一种测量材料动态力学性能的有效方法，通过高速应变测量，可以获取材料在高应变率下的应力-应变曲线。本研究中提到的六种棒材错位类型对实验结果的影响如下： 1. 中性轴偏移：如果棒材的中性轴（无应力轴）与加载方向不一致，会导致内部应力分布不均匀，进而影响信号的清晰度。 2. 不均匀支撑高度：支撑装置的高度差异可能导致加载过程中棒材受力不均，产生额外的弯曲应力，进而扭曲测量信号。 3. 非平行冲击面：当冲击面不平行时，会引入侧向力，使应变测量出现偏差，造成信号畸变。 4. 棒材直线度：如果棒材存在弯曲或扭曲，将导致应力波在传播过程中的变形，影响测量结果的准确性。 5. 穹顶效应：棒材端部的穹顶形状可能导致应力波反射和聚焦，进一步干扰信号的读取。 6. 中心圆孔的不规则：中心圆孔的几何形状不规则可能会影响冲击波的传输，引起信号失真。通过使用ANSYS-LSDYNA进行数值模拟，研究人员能够仿真这些错位情况，观察和量化它们对信号的影响，从而提出改善实验设置和数据解释的策略。这种数值模拟方法为理解复杂物理现象提供了便利，减少了实际实验中的时间和成本。这篇论文强调了在SHPB实验中对棒材对准精度的重视，并展示了ANSYS-LSDYNA作为工具在模拟和解析此类问题中的应用价值。对于从事材料科学、工程力学和相关领域的研究者来说，这是一项重要的参考，有助于提高实验设计和数据分析的精确度。

sub-cases were studied in the inclination error; which were

equivalent to the bar rotation (

) in a range of 0.03125e1



(Fig. 2b

and Table 2). In these two cases, the bars were maintained to be in

perfect condition, which were having a straight neutral axis and

perpendicular impact faces. Therefore, these cases were not related

to the quality of bar production. These two cases might occur in the

physical experiment when the bars were not aligned properly.

In the next four cases, the related bar production quality were

studied, i.e. non-parallel impact face, bar straightness, and dome

and cone impact face shapes. Case C studied the effect of non-

parallel impact face by varying the angle of impact face (

) from

0.03125 to 1



(Fig. 2c and Table 3). In the physical experiment, this

misalignment might occur if the ﬁnal ﬁnishing (grinding) of the

impact face was not perpendicular to the neutral axis.

Case D (Fig. 2d) studied the effect of bar straightness. This is one

of the most common problems with the bar. It is necessary to

ensure that the neutral axis of the bar is straight enough to satisfy

the requirement of one-dimensional stress wave propagation. The

straightness tolerances (per 1 m length) were varied from 0.251 to

4.372 mm (Table 4).

Cases E and F (Fig. 2e and f) studied the effects of the dome and

cone impact face shapes, respectively. The dome heights and cone

depths were varied from 0.0069 to 0.2217 mm (Table 5 for case E

and Table 6 for case F). These problems might arise when the

impact faces were machined using a lathe without ﬁnal ﬁnishing

using a grinding process.

Based on the way that the two impact faces make contact, the

above six cases can be classiﬁed into three groups: I. parallel (case

A), II. non-parallel (cases B, C and D) and III. symmetrically non-

parallel (cases E and F). Numerical simulations were used to

examine the effect of each case and identify the tolerance values for

each case.

3.2. Finite element modeling

Comprehensive numerical simulations (a total of 24 sub-cases)

were conducted to simulate the misalignment effects in the SHPB

technique. This modeling was based on the SHPB in our laboratory.

The diameter of the bar was 12.7 mm, while the length of the

striker bar was 300 mm. The input bar has the same length as the

output bar which was 1000 mm. The bars were made from high

strength steel (AISI 4140). The tensile strength, density, Young’s

modulus and Poisson’s ratio were 850 MPa, 7769 kg/m

, 205 GPa

and 0.29, respectively. These data were provided by the supplier.

The numerical simulations were divided into two main sections,

i.e. bar calibration and conventional SHPB testing. The bar calibra-

tion test, which is to determine the strain and stress correction

factors, is the most crucial step prior the real test. The former factor

is determined by impacting the striker bar on the input bar and the

output bar separately (“bar apart”), while the latter factor is

determined by impacting the striker bar on the coupled

inputeoutput bars with no specimen in between (“bars together”).

The shape of the incident and transmitted waves generated from

the “bars together” testing should be similar. Gama et al. [10]

suggested that the parallelism of the bar interfaces should be

checked if these wave shapes were not alike, though no speciﬁc

tolerances were given. In the “bar apart” modeling, the “imperfect

bar”, representing each case studied (Cases A.1 to F.6), was

employed as the input bar. Meanwhile, in the “bars together”

modeling, the “imperfect bar” was employed as the output bar.

These arrangements were selected such that the effects of the bar

interfaces parallelism could be studied, as also suggested by Gama

et al. [10].

The conventional SHPB testing was also divided into two sub-

sections, i.e. input and output bar misalignments. In both studies,

a specimen was sandwiched between the input and output bars. In

the ﬁrst study, the contact surface between the specimen and

output bar was maintained parallel, while the contact surface

between the input bar and specimen depended on the condition of

each case. In the second study, the contact surface between the

input bar and specimen was maintained parallel, while the contact

surface between the specimen and output bar depended on the

condition of each case (vice versa of the ﬁrst study).

Fig. 3 shows an example of the ﬁnite element (FE) modeling

details of “bar apart” testing. This model consists of four parts:

striker bar, input bar, propulsion barrel and O-ring support. An

automatic hexagonal meshing was selected with an element size of

1.5 mm. Our studies [18] showed that the results were insensitive to

the mesh smaller than 1.5 mm.

The sampling rate of the numerical simulations was selected to

be 1

s with a time step formula based on the bar wave velocity. A

termination time was selected to be 500

s. The constant stress

solid element property was selected for all parts. A ﬁxed support

was selected for propulsion barrel and O-ring support nodes.

In the bar calibration modeling (Section 4.1), two materials, i.e.

elastic (MAT 1.1 for the bars) and rigid (MAT 20.1 for the propulsion

barrel and O-ring support) were employed. The elastic material

model will fail to simulate the real physical experiment at the input

bar impact end for cases E and F. This is due to the fact that the

element at the impact face might be plastically deformed during

the impact of the striker bar. However, the elastic material model

will be valid for the remaining sections of the bar because these

sections will be in an elastic state. Thus, the elastic material model

will also be employed for the numerical simulation parameters in

cases E and F.

Table 2

Case B e uneven support height.

Descriptions Case B.1 Case B.2 Case B.3 Case B.4 Case B.5 Case B.6

Y, mm 0.545 1.091 2.182 4.363 8.727 17.452

Z, mm 1000 1000 1000 1000 1000 1000

Bar rotation (

), degree 0.03125 0.0625 0.125 0.25 0.5 1.0

Table 3

Case C e unparallel impact face.

Descriptions Case C.1 Case C.2 Case C.3 Case C.4 Case C.5 Case C.6

Impact end angle

(

), degree

0.03125 0.0625 0.125 0.25 0.5 1.0

Table 4

Case D e bar straightness.

Properties Case D.1 Case D.2 Case D.3 Case D.4 Case D.5 Case D.6

Straightness tolerance,

mm (per 1 m)

0.251 0.273 0.547 1.093 2.186 4.372

Equivalent radius of

curvature, m

500 459.28 229.64 114.82 57.41 28.71

Equivalent impact end

angle (

), Degree

0.057 0.0625 0.125 0.25 0.5 1.0

M.A. Kariem et al. / International Journal of Impact Engineering 47 (2012) 60e7062

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使用ANSYS-LSDYNA模拟SHPB实验中棒材错位影响

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