沖擊頻率對低應(yīng)力多沖碰撞塑性變形的影響研究及建模
發(fā)布時(shí)間：2019-02-09 11:05
【摘要】：工程中許多關(guān)鍵零部件在應(yīng)力遠(yuǎn)小于材料屈服極限的多次沖擊碰撞工況下仍會發(fā)生宏觀累積塑性變形,進(jìn)而產(chǎn)生失效,給企業(yè)帶來安全隱患和經(jīng)濟(jì)損失。因此對低應(yīng)力多沖碰撞塑性變形的研究具有重要的工程意義。低應(yīng)力多沖碰撞塑性變形的影響因素眾多,如材料性能、沖擊應(yīng)力、沖擊次數(shù)等。加載頻率是材料動態(tài)力學(xué)響應(yīng)過程中非常重要的影響因素,加載頻率不同,零部件的力學(xué)響應(yīng)可能不同。本文重點(diǎn)研究沖擊頻率對低應(yīng)力多沖碰撞塑性變形的影響,并建立累積塑性形變量與相關(guān)影響因素的數(shù)學(xué)關(guān)系模型,為工程應(yīng)用中低應(yīng)力多沖碰撞工況下零構(gòu)件形變量和壽命的預(yù)測、加載條件的設(shè)計(jì)等提供理論指導(dǎo)。選用純鐵和45鋼作為試驗(yàn)材料,對每種材料分別進(jìn)行兩組不同沖擊頻率下的低應(yīng)力多沖碰撞試驗(yàn)。每組包含三個(gè)試驗(yàn),對應(yīng)三種不同的沖擊頻率(0.25Hz、1Hz、4Hz),三個(gè)試驗(yàn)的沖擊載荷初速度、沖擊應(yīng)力和沖擊次數(shù)均一致。各組試驗(yàn)結(jié)果均表明,沖擊頻率越大,總累積塑性形變越大;由單層形變率及硬化程度與距沖擊表層深度的關(guān)系曲線分析,總體上單層形變率、硬化程度也隨沖擊頻率的增加而增大;總形變量、單層形變率均隨沖擊頻率的增加而非線性變化,頻率越大,總形變及單層形變率的增加量越小。純鐵材料在低應(yīng)力多沖碰撞后,微觀組織中有明顯的穿晶裂紋,鐵素體晶粒存在碎化現(xiàn)象。頻率越大,晶粒碎化現(xiàn)象則越嚴(yán)重,形變率也越大。45鋼材料在低應(yīng)力多沖碰撞后,微觀組織中珠光體晶粒碎化嚴(yán)重,未破碎的珠光體晶粒中可觀察到明晰的亞晶界,網(wǎng)狀鐵素體有壓縮細(xì)化的現(xiàn)象。沖擊頻率越大,網(wǎng)狀鐵素體含量則越少,其細(xì)化程度越大,珠光體晶粒碎化現(xiàn)象也越嚴(yán)重,最終形變量也越大。分析認(rèn)為低應(yīng)力多沖碰撞塑性形變的產(chǎn)生主要是由于沖擊載荷的熱激活作用促使位錯(cuò)彎結(jié)的產(chǎn)生,降低了位錯(cuò)滑移的臨界切應(yīng)力,多次沖擊碰撞造成彎結(jié)沿位錯(cuò)線傳播,產(chǎn)生位錯(cuò)滑移應(yīng)變。沖擊載荷初速度及沖擊應(yīng)力不變時(shí),沖擊頻率越大,原子易動性越大,越易產(chǎn)生位錯(cuò)滑移,多次沖擊碰撞后,最終累積形變量越大。在沖擊碰撞試驗(yàn)的基礎(chǔ)上,結(jié)合國內(nèi)外沖擊碰撞、微形變的研究成果,建立了累積塑性形變量與沖擊次數(shù)、沖擊應(yīng)力、沖擊頻率的S-N-σ-f數(shù)學(xué)關(guān)系模型。定義沖擊次數(shù)N、沖擊頻率f無窮大時(shí),總累積塑性形變不超過主要屈服區(qū)(10mm)0.2%時(shí)的最大應(yīng)力值為應(yīng)力閾值σc,可表征金屬材料抗低應(yīng)力多沖碰撞塑性變形的能力。由純鐵和45鋼對應(yīng)數(shù)學(xué)模型的相關(guān)參數(shù)對比分析表明,45鋼材料抗低應(yīng)力多沖碰撞塑性形變的能力強(qiáng)于純鐵材料;純鐵材料累積塑性形變量隨沖擊次數(shù)的增加而增大的速率大于45鋼材料。
[Abstract]:In engineering, many key parts will still have macroscopic cumulative plastic deformation under the condition of multiple impact collisions where the stress is far less than the material yield limit, which will lead to failure and bring safety hidden trouble and economic loss to enterprises. Therefore, the study of low stress multiple impact plastic deformation has important engineering significance. There are many factors influencing the plastic deformation of low stress impact, such as material properties, impact stress, impact times and so on. Loading frequency is a very important factor in the process of dynamic mechanical response of materials. The mechanical response of parts may be different with different loading frequency. In this paper, the effect of impact frequency on plastic deformation of low stress and multiple impact is studied, and a mathematical model of cumulative plastic shape variable and related influencing factors is established. It provides theoretical guidance for the prediction of the shape variable and life of the zero member under the condition of multi-impact and low stress impact, and the design of loading conditions. Pure iron and 45 steel were selected as test materials. Two groups of low stress and multiple impact tests were carried out on each material at different impact frequencies. Each group consists of three tests, corresponding to three different impact frequencies (0.25 Hz / 1 Hz). The initial velocity of the impact load, the impact stress and the impact times of the three tests are the same. The experimental results show that the larger the impact frequency, the greater the total cumulative plastic deformation. From the analysis of the relationship curve between the single layer deformation rate and hardening degree and the depth from the impact surface, it is found that the single layer deformation rate and hardening degree also increase with the increase of impact frequency. The total deformation and monolayer deformation rate are all nonlinear with the increase of shock frequency. The larger the frequency, the smaller the increase of total deformation and monolayer deformation rate. There are obvious transgranular cracks in the microstructure of pure iron materials after low stress and multiple impact, and the ferrite grains are broken. The higher the frequency, the more serious the phenomenon of grain fragmentation and the greater the deformation rate. 45 steel materials in the low stress impact, pearlite grains in the microstructure of serious fragmentation, unbroken pearlite grains can be observed in clear sub-grain boundaries, The reticular ferrite has the phenomenon of compression and refinement. The larger the impact frequency, the less the ferrite content, the greater the degree of refinement, the more serious the grain fragmentation of pearlite and the greater the final shape variable. It is considered that the plastic deformation of low stress and multiple impact is mainly caused by the thermal activation of impact load, which results in the formation of dislocation bend, which reduces the critical shear stress of dislocation slip and propagates along the dislocation line due to multiple impact collisions. The dislocation slip strain is produced. When the initial velocity of impact load and impact stress are constant, the larger the impact frequency is, the greater the mobility of atoms is, the easier it is to produce dislocation slip, and the larger the final cumulative deformation is after multiple impact collisions. On the basis of impact test, combined with the research results of impact and micro-deformation at home and abroad, the S-N- 蟽 -f mathematical model of cumulative plastic shape variable and impact times, impact stress and impact frequency is established. The maximum stress value when the total cumulative plastic deformation does not exceed the main yield zone (10mm) 0.2 is defined as the stress threshold 蟽 _ c when the impact number N and the impact frequency f are infinite, which can be used to characterize the ability of metal materials to resist low stress and multiple impact plastic deformation. The comparison and analysis of relative parameters between pure iron and 45 steel show that 45 steel has better resistance to low stress and multiple impact plastic deformation than pure iron. The accumulative plastic shape variable of pure iron material increases with the increase of impact times and the rate of increase is greater than that of 45 steel material.
【學(xué)位授予單位】：蘇州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG115
本文編號：2418893
[Abstract]:In engineering, many key parts will still have macroscopic cumulative plastic deformation under the condition of multiple impact collisions where the stress is far less than the material yield limit, which will lead to failure and bring safety hidden trouble and economic loss to enterprises. Therefore, the study of low stress multiple impact plastic deformation has important engineering significance. There are many factors influencing the plastic deformation of low stress impact, such as material properties, impact stress, impact times and so on. Loading frequency is a very important factor in the process of dynamic mechanical response of materials. The mechanical response of parts may be different with different loading frequency. In this paper, the effect of impact frequency on plastic deformation of low stress and multiple impact is studied, and a mathematical model of cumulative plastic shape variable and related influencing factors is established. It provides theoretical guidance for the prediction of the shape variable and life of the zero member under the condition of multi-impact and low stress impact, and the design of loading conditions. Pure iron and 45 steel were selected as test materials. Two groups of low stress and multiple impact tests were carried out on each material at different impact frequencies. Each group consists of three tests, corresponding to three different impact frequencies (0.25 Hz / 1 Hz). The initial velocity of the impact load, the impact stress and the impact times of the three tests are the same. The experimental results show that the larger the impact frequency, the greater the total cumulative plastic deformation. From the analysis of the relationship curve between the single layer deformation rate and hardening degree and the depth from the impact surface, it is found that the single layer deformation rate and hardening degree also increase with the increase of impact frequency. The total deformation and monolayer deformation rate are all nonlinear with the increase of shock frequency. The larger the frequency, the smaller the increase of total deformation and monolayer deformation rate. There are obvious transgranular cracks in the microstructure of pure iron materials after low stress and multiple impact, and the ferrite grains are broken. The higher the frequency, the more serious the phenomenon of grain fragmentation and the greater the deformation rate. 45 steel materials in the low stress impact, pearlite grains in the microstructure of serious fragmentation, unbroken pearlite grains can be observed in clear sub-grain boundaries, The reticular ferrite has the phenomenon of compression and refinement. The larger the impact frequency, the less the ferrite content, the greater the degree of refinement, the more serious the grain fragmentation of pearlite and the greater the final shape variable. It is considered that the plastic deformation of low stress and multiple impact is mainly caused by the thermal activation of impact load, which results in the formation of dislocation bend, which reduces the critical shear stress of dislocation slip and propagates along the dislocation line due to multiple impact collisions. The dislocation slip strain is produced. When the initial velocity of impact load and impact stress are constant, the larger the impact frequency is, the greater the mobility of atoms is, the easier it is to produce dislocation slip, and the larger the final cumulative deformation is after multiple impact collisions. On the basis of impact test, combined with the research results of impact and micro-deformation at home and abroad, the S-N- 蟽 -f mathematical model of cumulative plastic shape variable and impact times, impact stress and impact frequency is established. The maximum stress value when the total cumulative plastic deformation does not exceed the main yield zone (10mm) 0.2 is defined as the stress threshold 蟽 _ c when the impact number N and the impact frequency f are infinite, which can be used to characterize the ability of metal materials to resist low stress and multiple impact plastic deformation. The comparison and analysis of relative parameters between pure iron and 45 steel show that 45 steel has better resistance to low stress and multiple impact plastic deformation than pure iron. The accumulative plastic shape variable of pure iron material increases with the increase of impact times and the rate of increase is greater than that of 45 steel material.
【學(xué)位授予單位】：蘇州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG115
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