【摘要】：混凝土在使用過(guò)程中,由于長(zhǎng)期荷載、環(huán)境腐蝕、材料老化、構(gòu)件破損等因素作用,混凝土內(nèi)部逐漸產(chǎn)生損傷積累,使結(jié)構(gòu)的承載能力和耐久性能下降,減少了結(jié)構(gòu)的使用壽命。如何有效地預(yù)測(cè)在役混凝土的損傷演變情況是當(dāng)前混凝土工程亟待解決的關(guān)鍵性問(wèn)題之一。鑒于此,本文在線(xiàn)性及非線(xiàn)性聲學(xué)波動(dòng)理論基礎(chǔ)上,研究混凝土隱蔽裂縫形態(tài)參數(shù)與波動(dòng)傳播特性的相關(guān)性規(guī)律,為更好的實(shí)現(xiàn)對(duì)混凝土材料探測(cè)提供理論基礎(chǔ)和應(yīng)用參考,主要研究?jī)?nèi)容及結(jié)論如下:1)對(duì)養(yǎng)護(hù)好的含不同形態(tài)參數(shù)裂縫的混凝土試件進(jìn)行超聲波測(cè)試試驗(yàn),采用快速傅立葉變換和小波分析等信號(hào)處理技術(shù)實(shí)現(xiàn)了對(duì)聲波信號(hào)參數(shù)的提取,研究零應(yīng)力狀態(tài)下裂縫的存在對(duì)混凝土超聲參數(shù)的影響。試驗(yàn)表明:零應(yīng)力狀態(tài)下,混凝土試件內(nèi)有裂縫時(shí)的波速比試件內(nèi)無(wú)裂縫時(shí)小,但裂縫尺寸不大時(shí)變化幅度小,較難區(qū)分;裂縫寬度對(duì)波速影響明顯,深度其次,裂縫走向與聲波傳播方向夾角對(duì)波速無(wú)影響。2)零應(yīng)力狀態(tài)下,采用快速傅立葉變換和頻譜分析的方法得到混凝土的聲學(xué)參數(shù),與完整試件相比,有裂縫的試件其裂縫形態(tài)參數(shù)對(duì)最大振幅影響明顯,且裂縫走向與聲波傳播方向重合時(shí)最大振幅的值最小,裂縫走向與聲波傳播方向垂直時(shí)時(shí)域最大振幅的值最大。除主頻外,各參數(shù)隨裂縫形態(tài)參數(shù)變化規(guī)律相似。裂縫對(duì)頻域最大振幅和譜面積影響規(guī)律基本相同,均隨裂縫尺寸的增加而下降。3)開(kāi)展了單軸受載混凝土的超聲波測(cè)試試驗(yàn),分析了裂縫不同形態(tài)參數(shù)混凝土超聲參數(shù)與應(yīng)力相關(guān)性的影響,試驗(yàn)結(jié)果表明:受荷條件下試件內(nèi)有裂縫時(shí),基本規(guī)律是裂縫尺寸越大,隨應(yīng)力變化波速下降越快,且在試件破壞時(shí)其波速的最小值越小。相比于裂縫寬度,裂縫深度對(duì)試件波速與應(yīng)力敏感性的影響較弱。裂縫與超聲波傳播方向的夾角不同的幾種情況中,裂縫與超聲波傳播方向重合即夾角為0°時(shí)隨著應(yīng)力的增加波速下降速率最大。4)通過(guò)小波變換得到的加權(quán)譜面積,在一定程度上濾除了高頻干擾并考慮了不同尺度間權(quán)重的差異,對(duì)應(yīng)力有較強(qiáng)的敏感性。含不同形態(tài)參數(shù)裂縫的試件,加載時(shí)加權(quán)譜面積變化規(guī)律基本相同,即隨應(yīng)力增加,裂縫尺寸越大加權(quán)譜面積變化幅度越明顯。加權(quán)主頻幅值與加權(quán)譜面積隨應(yīng)力變化趨勢(shì)大致相同,均在超過(guò)試件極限應(yīng)力的70%后急劇下降,這可能是由于裂縫貫通所致,表明出現(xiàn)了不可逆的塑性變形,試件已接近破壞。5)主頻與混凝土內(nèi)部結(jié)構(gòu)狀態(tài)和外部應(yīng)力狀態(tài)均無(wú)關(guān)。零應(yīng)力狀態(tài)下試件內(nèi)有無(wú)裂縫對(duì)主頻影響不大,受荷條件下,隨著應(yīng)力的增加,主頻也基本不改變6)通過(guò)分析零應(yīng)力狀態(tài)下缺陷尺度與超聲波波長(zhǎng)的關(guān)系,在此基礎(chǔ)上利用含裂縫混凝土的等效彈性參數(shù),建立了零應(yīng)力狀態(tài)下不同缺陷分布所引起的超聲波慢度的變化關(guān)系。通過(guò)分析單個(gè)微裂紋影響下微裂紋的擴(kuò)展作用機(jī)理和單個(gè)微裂紋擴(kuò)展的混凝土損傷本構(gòu)關(guān)系,建立了用聲參數(shù)表征的混凝土損傷本構(gòu)模型,并將理論與試驗(yàn)結(jié)果進(jìn)行了對(duì)比,結(jié)果表明用波速表示的混凝土損傷本構(gòu)模型能較好地反映應(yīng)力變化對(duì)波速的影響規(guī)律。
[Abstract]:In the process of use, due to the factors such as long-term load, environmental corrosion, material aging and component breakage, the damage and accumulation are gradually generated in the concrete, so that the bearing capacity and the durability of the structure can be reduced, and the service life of the structure is reduced. How to predict the damage and evolution of active concrete is one of the key problems to be solved urgently. In view of this, on the basis of the theory of linear and non-linear acoustic wave, this paper studies the relationship between the morphological parameters and the wave propagation characteristics of the concrete concealed crack, and provides the theoretical basis and application reference for the better realization of the concrete material detection. The main research contents and conclusions are as follows: 1) carrying out the ultrasonic testing test on the cured concrete test piece containing the different shape parameter cracks, and adopting the signal processing technology such as fast Fourier transform and wavelet analysis to realize the extraction of the acoustic wave signal parameters, The influence of the existence of the crack under the zero stress state on the ultrasonic parameters of the concrete is studied. The test shows that under the condition of zero stress, the wave velocity of the crack in the concrete test piece is less than that in the test piece, but the change of the crack size is small, it is difficult to distinguish, the crack width is obviously affected by the wave velocity, the depth is the second, In that condition of zero stress, the acoustic parameters of the concrete are obtained by the method of fast Fourier transform and frequency spectrum analysis. And the maximum amplitude value is the largest when the crack trend coincides with the acoustic wave propagation direction, and the maximum amplitude value of the time domain is the largest when the crack moves to be perpendicular to the sound wave propagation direction. In addition to the main frequency, the parameters of each parameter are similar with the change of the shape parameters of the crack. The influence of the crack on the maximum amplitude and the spectral area of the frequency domain is the same, which decreases with the increase of the size of the crack. In that case of crack in the specimen under load condition, the basic law is that the larger the crack size, the faster the wave velocity decreases with the stress change, and the smaller the minimum value of the wave velocity when the specimen is broken. The effect of crack depth on the test piece's wave velocity and stress sensitivity is weak compared with the crack width. when the included angle between the crack and the propagation direction of the ultrasonic wave is different, the crack is coincident with the propagation direction of the ultrasonic wave, that is, when the included angle is 0 degree, The high-frequency interference is filtered to a certain extent and the difference of the weights between different scales is taken into account, and the sensitivity to the stress is strong. The change of the weighted spectral area of the test piece with different shape parameters is basically the same, that is, with the increase of the stress, the larger the crack size and the change of the weight spectrum area. The weighted main frequency amplitude and the weighted spectral area are about the same as the stress change trend, and are sharply reduced after exceeding 70% of the limit stress of the test piece, which can be caused by the crack penetration, indicating that the irreversible plastic deformation occurs, The test piece has been close to the damage.5) The main frequency is not related to the internal structure state and the external stress state of the concrete. Under the condition of zero stress, the existence of cracks in the test piece has little influence on the main frequency, under the load condition, with the increase of the stress, the main frequency is basically not changed by 6), and by analyzing the relation between the defect scale and the ultrasonic wave length in the zero stress state, the equivalent elastic parameter containing the crack concrete is utilized. The change of the ultrasonic slowness caused by the distribution of different defects in the zero-stress state is established. By analyzing the extension action mechanism of the micro-crack under the influence of a single micro-crack and the concrete damage constitutive relation of a single micro-crack propagation, a concrete damage constitutive model characterized by acoustic parameters is established, and the theory is compared with the test result. The results show that the concrete damage constitutive model expressed by the wave velocity can better reflect the influence of the stress change on the wave velocity.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TU528

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