摆锤刀刃半径对夏比冲击试验结果的影响

采用8mm和2mm两种摆锤刀刃半径分别对低、中、高3个冲击吸收能量等级的3种锻件钢材进行了系列温度夏比冲击对比试验,研究了摆锤刀刃半径对冲击吸收能量、侧膨胀值、剪切断面率以及韧脆转变温度的影响。结果表明:低、中、高能量3种钢材的对比试验都呈现出较为明显的差异,即采用8mm摆锤刀刃半径测得的冲击吸收能量要高于采用2mm摆锤刀刃半径测得的,但是该种差异在上、下平台附近时逐步缩小;用两种摆锤刀刃半径测得的冲击延性指标,如侧膨胀值和剪切断面率也存在相对应的结果;不同摆锤刀刃半径系列温度冲击试验测得同一材料的韧脆转变温度也不相同。     

摆锤刀刃半径对夏比V型冲击吸收能量的影响

为研究不同尺寸摆锤刀刃锤头对冲击试验结果的影响,采用刀刃圆角半径分别为2mm和8mm的锤头对多种材料进行夏比V型冲击试验,并从吸收能量、断口形貌等方面分析V型缺口试样在2mm摆锤刀刃下的冲击吸收能量K_(V2)与8mm摆锤刀刃下的冲击吸收能量K_(V8)的变化规律,研究摆锤刀刃尺寸对夏比V型冲击吸收能量的影响。结果表明:在韧脆转变温度曲线上平台区和转变区(塑性断口)范围内,K_(V8)大于K_(V2);在转变区(脆性断口)范围内,K_(V2)大于K_(V8);在下平台区,KV8与K_(V2)几乎相等。     

摆锤刀刃半径对SA508Gr.3Cl.2钢冲击试验结果的影响

冲击试验标准ASTM E23—16b和EN 10045-1:1990,对于摆锤刀刃半径的要求分别为8mm和2 mm,为了研究这两种摆锤刀刃半径对于冲击试验结果的影响,依据这两个标准对SA508Gr.3Cl.2钢进行了系列温度冲击试验,并对断口形貌进行了观察。结果表明:摆锤刀刃半径对冲击吸收能量、侧膨胀值、剪切断面率以及韧脆转变温度等均有影响;总体上在韧性区和脆性区即低能量和高能量范围内,2 mm摆锤刀刃半径测得的数值小于8 mm摆锤刀刃半径测得的,在韧脆转变温度范围内,两者之间没有明显的大小关系。     

不同摆锤刀刃半径对室温冲击试验结果的影响

目前的冲击试验国家标准GB/T 229-2007中规定,冲击试验时摆锤刀刃半径应为2mm和8mm两种,但采用两种不同刀刃半径进行试验后的结果会存在一定的偏差。因此采用两种不同半径的刀刃分别对同一批试样进行室温冲击试验,结果表明:8mm半径刀刃冲击后得出的冲击吸收功略大于2mm半径刀刃的冲击吸收功,但差异不是很明显;检测中必须采用正确的试验方法,选择相对应的刀刃半径,避免造成检测结果的误判;对不同材料进行冲击性能比较时,只有选用相同半径的摆锤刀刃进行检测,结果才具有可比性。     

试样厚度对夏比冲击试验结果的影响

通过不同温度下的夏比摆锤冲击试验对非标准小尺寸V型缺口冲击试样的冲击吸收能量和侧膨胀值进行了分析,并结合力-位移曲线,研究了试样厚度对冲击试验结果的影响。结果表明:当试验温度高于韧脆转变温度时,冲击吸收能量与试样的横截面积有关,因此与厚度呈线性关系;而低于韧脆转变温度时,冲击吸收能量与试样厚度之间没有明显关系;试样的侧膨胀值、剪切断面率与厚度之间没有直接联系。随着试样厚度的减小,不稳定裂纹扩展起始力越来越小,从而导致冲击吸收能量减小。厚度越大试样吸收的能量越多,冲击过程中所受到的最大力也越大。     

核电工程用冲击试验标准对比分析

我国核电工程冲击试验通常采用GB/T 229-2007和ASTM E23-2007a两种标准,以核电工程常用的SA-508Gr.3Cl.1钢和SA-182F316LN钢为研究对象,从冲击吸收能量和韧脆转变温度两方面对比分析了两种标准的差异。结果表明:GB/T 229-2007更严格,按此标准测得的冲击吸收能量比按照ASTM E23-2007a测得的要低;当SA-508Gr.3Cl.1钢的试验温度高于韧脆转变温度时,采用两种标准测得的冲击吸收能量差值均随温度升高而增大;当温度低于韧脆转变温度时,采用两种标准测得的冲击吸收能量较接近;SA-182F316LN钢在试验温度范围内,按照ASTM E23-2007a测得的冲击吸收能量均比按照GB/T 229-2007测得的要高,且在-80℃两者差别最大。建议在充分积累核电工程材料冲击性能数据的基础上,逐步采用GB/T 229-2007进行核电材料冲击性能评价。     

L360管线钢的韧脆转变温度

研究了L360管线钢在冲击试验过程中各阶段能量的变化与温度、断口形态的关系,并采用几种方法对L360管线钢的韧脆转变温度进行了评定。结果表明：几种方法测得L360钢的韧脆转变温度都低于-40℃。     

摆锤刀刃半径对冲击试验结果的影响

在各最新版本的冲击试验标准中,R_2和R_8两种规格的冲击摆锤刀刃都被认可采用,但两者产生的数据差异一直存在很大的争议。以3个标样供货机构的多种标准试样为试验对象,研究了两种摆锤刀刃半径对冲击试验结果的影响。结果表明:对于V型缺口低能量试样,R_2和R_8两种刀刃产生的差别并不会高于标准试样本身均匀度的影响,试验结果与试样本身的性能特征有关;对于弧形试样,采用R_8刀刃测得的冲击吸收能量高于采用R_2刀刃测得的,且试样韧性越好两者之间差别越大。     

冲击缺口类型对34CrNi1Mo钢韧脆转变温度的影响

对34CrNi1Mo钢分别进行V形和U形两种缺口类型的冲击试验,并绘制出剪切断面率与试验温度的曲线。通过曲线及韧脆转变温度的对比,分析缺口类型对34CrNi1Mo钢韧脆转变温度的影响。结果表明:不同缺口类型对34CrNi1Mo钢的韧脆转变温度有较大影响,U形缺口试样测得的韧脆转变温度低于V形缺口试样测得的韧脆转变温度。     

夏比V型冲击试验的尺寸效应及工程应用

以Q245R钢板为对象,进行不同尺寸试样在系列温度下的夏比V型冲击试验,论证试验的尺寸效应。结果表明:不同尺寸试样获得的冲击吸收能量一般不可换算,且与试样截面积没有对应关系。不同尺寸试样获得的韧脆转变温度数据也不可直接比较,随着试样尺寸减小,韧脆转变温度向低温方向移动。低温条件下,小尺寸试样可能导致材料韧性被高估,建议对小尺寸试样的试验温度进行调整。     

Influence of striking edge radius (2 vs. 8?mm) on instrumented Charpy data and absorbed energies

The most commonly used test standards for performing Charpy impact tests (ISO 148 and ASTM E 23) envisage the use of strikers having different radii of the striking edge, i.e. 2 mm (ISO) and 8 mm (ASTM). The effect of striker geometry on Charpy results was extensively studied in the past in terms of absorbed energy measured by the machine encoder, but few investigations are available on the influence of striker configuration on the results of instrumented Charpy tests (characteristic forces, displacements and integrated energy). In this paper, these effects are investigated based on the analysis of published results from three interlaboratory studies and some unpublished Charpy data obtained at SCK·CEN. The t-test was used for establishing the statistical significance of the observed effects. The instrumented variables which are the most sensitive to the radius of the striking edge are the maximum force and its corresponding displacement, with 8 mm-strikers providing systematically higher values. The effect on general yield forces, on the other hand, is less consistent and more difficult to rationalize, although 2 mm-strikers generally tend to deliver higher values. Absorbed energies, obtained both from the instrumented trace and from the pendulum encoder, are almost insensitive to the type of striker up to 200 J. For higher energy levels, the values obtained from 8 mm-strikers become progressively larger. Data scatter is generally higher for 2 mm-strikers.     

苹果碰撞损伤规律的研究

以天津蓟县苹果为试验对象,通过悬摆式碰撞试验,得到了苹果碰撞过程的加速度-时间曲线及其数学表达式,并分析了各碰撞参数对损伤体积的影响.研究表明,吸收能量、跌落角度、峰值加速度、恢复系数对损伤体积的预测较为明显.     

A study on the low-velocity impact response of laminates for composite railway bodyshells

This paper presents a study on the low-velocity impact response of woven fabric laminates for the composite bodyshell of a tilting railway vehicle. In this study, low-velocity impact tests for the three laminates with size of 100 mm × 100 mm were conducted at three impact energy levels of 2.4 J, 2.7 J and 4.2 J. Based on these tests, the impact force, the absorbed energy and the damaged area were investigated according to different energy levels and stacking sequences. The damage area was evaluated by visual inspection and C-scan measurement. The test results showed that the absorbed energy of [fill]₈ laminate was highest whereas [fill₂/warp₂]_s laminate was lowest. The [fill]₈ laminate had the largest delamination area because of the highest impact energy absorption.     

Impact damage in GFRP: New insights with infrared thermography

The aim of the present paper was to investigate the behaviour of glass fibres reinforced polymer (GFRP) under low velocity impact with infrared thermography. Several specimens were considered which include unidirectional E-glass fibres embedded in epoxy resin matrix with symmetrical stacking sequence [0₂/90₂]_S. These specimens were impacted with modified Charpy pendulum by varying shape (ogival and hemispherical) and diameter (18 and 24 mm) of the hammer and the impact energy in the range 4–25 J. The side opposite to impact was monitored by infrared cameras. Sequences of images were acquired with starting and ending times set so as to include the evolution of thermal phenomena from thermo-elastic to thermoplastic phases. Infrared thermography was also used for non-destructive evaluation of specimens before and after impact. The obtained results show that on-line monitoring of the impact is useful for material characterization. In particular, it is shown that the onset of heat generation loci corresponds to the onset of impact damage. From the analysis of temperature maps it is possible to get information about damage threshold and extension. One main finding regards the relationship between the damaged area and the effective striking surface.     

Instrumented impact test of duplex stainless steel miniature specimen

The paper describes a new approach to characterize metallic materials by a novel instrumented notch impact test for samples with small specimen size. A piezo‐electric sensor mounted on the pendulum hammer provides force information during the fracture process. By numerical integration of the signal the absorbed impact energy can be calculated very exactly. Further information about the fracture behavior can be extracted from the resulting force‐displacement‐diagram. Several duplex stainless steels in different heat treatment conditions were tested and compared to standard Charpy impact testing specimen. It is concluded that different grades of embrittlement of duplex materials can be detected with high accuracy. Due to a data acquisition rate of 250 kilo‐samples/second and limited stiffness of the pendulum hammer impact energies of less than 7% of maximum energy materials with high brittleness can only be characterized qualitatively.     

Woven glass/epoxy laminates subject to projectile impact

Impact results of woven E-glass/epoxy composite laminates are presented in this paper. A gas gun was employed to launch 12.7 mm diameter hemispherically-tipped projectiles 35.5 g in weight. The developed laser Doppler anemometer (LDA) system was successfully employed to record the projectile velocity history, whose range was from several m/s to twice the ballistic limit of the target, and was converted into the force history by using both the optimization and the polynomial curve-fitting methods. It was found that, when the projectile initial velocity was lower than the ballistic limit, the delamination area was approximately proportional to the initial energy of the projectile, and the relationship between the absorbed energy and initial energy of the projectile followed a straight line of unit slope when it was expressed non-dimensionally. Also, the incremental rate of the peak impact force became gradually smaller and finally reached a constant value at the ballistic limit, and the impact force history became progessively asymmetric. Beyond the ballistic limit, the absorbed energy remained approximately constant regardless of the increase of the initial striking velocity of the projectile. The peak impact force, on the other hand, was surprisingly found to increase again.     

Irreversibly absorbed energy and damage in GFRP laminates impacted at low velocity

The scope of this paper was to establish a correlation between the damage occurring in a composite as a consequence of low-velocity impact and the energy dissipated during the impact phenomenon. To this aim, instrumented impact tests were carried out on glass fabric/epoxy laminates of three different thicknesses, using different energy levels. The irreversibly absorbed energy was obtained from the force–displacement curves provided by the impact machine. To assess damage progression as a function of impact energy, ply-by-ply delamination and fibre breakages revealed by destructive tests were measured. A previous model, based on energy balance considerations, was applied to interpret the experimental results, together with an original method of data reduction, allowing for the isolation of the maximum energy portion due to indentation and vibrational effects. From the results obtained, the contribution of fibre breakage and matrix damage to the irreversibly absorbed energy is comparable at low impact energies; with increasing initial energy levels, delamination becomes predominant in determining energy dissipation. However, the critical energy-release rate required to propagate delamination, as calculated from impact data, is considerably higher than the typical values deriving from Mode II delamination tests performed under laboratory conditions.     

超高强钢制电池包底部球击试验与仿真方法研究

目的 研究超高强钢电池包底部球击工况的仿真分析方法,通过实物试验验证仿真分析方法的准确性。方法 通过建立电池包底部球击的仿真模型,对底部球击工况进行数值模拟,分析球击过程中应力–应变分布和底板承受变形的能量情况。开展底部球击实物试验,并与模拟结果进行对比分析。结果 在球击过程中,随着球击头撞击底板位移的增大,挤压力逐渐增加,底板变形能量也逐渐增加;当挤压力达到10 kN时,仿真位移为19.127 mm,试验结果位移为20 mm。当位移达到20 mm时,仿真底板变形能量为73.716 J,试验结果为70.581 J,仿真与试验结果较为一致。结论 超高强钢电池包在底部球击试验中未发生开裂,满足标准要求,数值模拟方法可以为电池包底部球击工况提供指导。     

High velocity impact response of Kevlar-29/epoxy and 6061-T6 aluminum laminated panels

The high velocity impact response of composite laminated plates has been experimentally investigated using a nitrogen gas gun. Tests were undertaken on sandwich structures based on Kevlar-29 fiber/epoxy resin with different stacking sequence of 6061-T6 Al plates. Impact testing was conducted using cylindrical shape of 7.62 mm diameter steel projectile at a range of velocities (180–400 m/s) were investigated to achieve complete perforation of the target. The numerical parametric study of ballistic impact caused by same conditions in experimental work is undertaken to predict the ballistic limit velocity, energy absorbed by the target and comparison between simulation by using ANSYS Autodyn 3D v.12 software and experimental work and study the effects of shape of the projectile with different (4, 8 and 12 mm) thicknesses on ballistic limit velocity. The sequence of Al plate position (front, middle and back) inside laminate plates of composite specimen was also studied. The Al back stacking sequence plate for overall results obtained was the optimum structure to resist the impact loading.The results obtained hereby are in good agreement with the experimental (maximum error of 3.64%) data where it has been shown that these novel sandwich structures exhibit excellent energy absorbing characteristics under high velocity impact loading conditions. Hence it is considered suitable for applications of armor system.