分析電子拉力試驗機測試塑料制品的性能

分析電子(zi)拉力試驗機測試塑料制品的性能：

        拉伸(shen)(shen)試(shi)(shi)(shi)驗(yan)(yan)(yan)要(yao)求(qiu)試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)做(zuo)成(cheng)(cheng)(cheng)啞鈴形(xing)或矩形(xing)。制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang)方(fang)式(shi)有兩種:一(yi)種是用原材(cai)(cai)料制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang);另(ling)一(yi)種是從制(zhi)(zhi)(zhi)品上直接(jie)取(qu)樣(yang)(yang)(yang)(yang)(yang)。用原材(cai)(cai)料制(zhi)(zhi)(zhi)成(cheng)(cheng)(cheng)試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)有兒種方(fang)法(fa):模(mo)壓(ya)成(cheng)(cheng)(cheng)型(xing)、注塑成(cheng)(cheng)(cheng)型(xing)、壓(ya)延成(cheng)(cheng)(cheng)型(xing)或吹(chui)膜成(cheng)(cheng)(cheng)型(xing)等，每種制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang)過(guo)(guo)程都要(yao)符合相關的(de)(de)標準。但不同(tong)(tong)方(fang)法(fa)制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang)的(de)(de)試(shi)(shi)(shi)驗(yan)(yan)(yan)結(jie)(jie)(jie)果(guo)不具(ju)有可比性。同(tong)(tong)一(yi)種制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang)方(fang)法(fa)，要(yao)求(qiu)工(gong)藝(yi)(yi)參數(shu)，如模(mo)具(ju)結(jie)(jie)(jie)構(gou)、成(cheng)(cheng)(cheng)型(xing)溫度(du)(du)(du)、成(cheng)(cheng)(cheng)型(xing)壓(ya)力、冷(leng)卻速率以(yi)及工(gong)藝(yi)(yi)過(guo)(guo)程也要(yao)相同(tong)(tong)，否(fou)則，塑料在(zai)成(cheng)(cheng)(cheng)型(xing)過(guo)(guo)程中的(de)(de)微(wei)觀(guan)結(jie)(jie)(jie)構(gou)，如結(jie)(jie)(jie)晶度(du)(du)(du)、分子取(qu)向等將有較大(da)(da)變化(hua)，直接(jie)影響試(shi)(shi)(shi)驗(yan)(yan)(yan)結(jie)(jie)(jie)果(guo)。塑料原材(cai)(cai)料壓(ya)片或成(cheng)(cheng)(cheng)膜后，再(zai)用制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang)機和標準切刀制(zhi)(zhi)(zhi)成(cheng)(cheng)(cheng)標準試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)。制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)(yang)(yang)切刀要(yao)規范(fan)鋒利，否(fou)則，試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)會(hui)有毛邊或劃損等缺(que)(que)陷(xian)(xian)。其次，試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)的(de)(de)尺寸規格要(yao)一(yi)致(zhi)，試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)的(de)(de)厚(hou)度(du)(du)(du)不同(tong)(tong)，試(shi)(shi)(shi)驗(yan)(yan)(yan)結(jie)(jie)(jie)果(guo)也不同(tong)(tong)。厚(hou)度(du)(du)(du)大(da)(da)的(de)(de)試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)，試(shi)(shi)(shi)驗(yan)(yan)(yan)結(jie)(jie)(jie)果(guo)偏小。圖1為聚乙烯(PE)試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)在(zai)拉伸(shen)(shen)速率為100 mm/min時，厚(hou)度(du)(du)(du)與拉伸(shen)(shen)強度(du)(du)(du)的(de)(de)關系田(tian)。由(you)圖1可見:試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)厚(hou)度(du)(du)(du)越(yue)(yue)大(da)(da)，試(shi)(shi)(shi)驗(yan)(yan)(yan)測(ce)得的(de)(de)拉伸(shen)(shen)強度(du)(du)(du)越(yue)(yue)低。由(you)于試(shi)(shi)(shi)樣(yang)(yang)(yang)(yang)(yang)越(yue)(yue)厚(hou)，使得缺(que)(que)陷(xian)(xian)的(de)(de)概率越(yue)(yue)高。這也符合聚合物的(de)(de)微(wei)觀(guan)缺(que)(que)陷(xian)(xian)理論(lun)。

常用的(de)(de)制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)方法，大多數采用機(ji)(ji)(ji)械加(jia)(jia)(jia)工(gong)(gong)的(de)(de)方法從(cong)(cong)塑(su)料制(zhi)(zhi)(zhi)品上取樣(yang)(yang)(yang)，然后在啞鈴(ling)(ling)制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)機(ji)(ji)(ji)上制(zhi)(zhi)(zhi)成I型試樣(yang)(yang)(yang)。這(zhe)種(zhong)方法的(de)(de)優點(dian)是簡便易行(xing)。但這(zhe)種(zhong)方法zui大的(de)(de)缺點(dian)是測試結(jie)果(guo)誤(wu)差太大。根據(ju)GB12001.3-89和GB 1039規定:用機(ji)(ji)(ji)加(jia)(jia)(jia)工(gong)(gong)或沖(chong)(chong)模制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)，試樣(yang)(yang)(yang)邊緣不(bu)得(de)有缺口和毛刺等缺陷，加(jia)(jia)(jia)工(gong)(gong)時不(bu)應使試樣(yang)(yang)(yang)受(shou)到過(guo)分的(de)(de)沖(chong)(chong)擊、擠(ji)壓(ya)和受(shou)熱。加(jia)(jia)(jia)工(gong)(gong)面(mian)(mian)應光(guang)潔。啞鈴(ling)(ling)制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)機(ji)(ji)(ji)從(cong)(cong)原理上屬于(yu)沖(chong)(chong)模制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)的(de)(de)方法。其制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)過(guo)程必然受(shou)到擠(ji)壓(ya)和沖(chong)(chong)擊，并且加(jia)(jia)(jia)工(gong)(gong)面(mian)(mian)(沖(chong)(chong)切(qie)面(mian)(mian))亦(yi)很難保證光(guang)潔。實踐(jian)結(jie)果(guo)表明:對于(yu)用沖(chong)(chong)模制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)與銑(xian)床機(ji)(ji)(ji)加(jia)(jia)(jia)工(gong)(gong)制(zhi)(zhi)(zhi)樣(yang)(yang)(yang)，測試結(jie)果(guo)出入很大，嚴重時只相(xiang)當于(yu)后者的(de)(de)一半。

1.3試樣裝夾

    在(zai)拉(la)伸試(shi)(shi)(shi)驗時，不容許試(shi)(shi)(shi)樣(yang)受到(dao)偏(pian)心(xin)力的(de)(de)作(zuo)用。因為(wei)它會(hui)使(shi)試(shi)(shi)(shi)樣(yang)產(chan)生附加彎(wan)曲應力，從而(er)造成試(shi)(shi)(shi)驗結果的(de)(de)偏(pian)差。對于脆(cui)性材(cai)料，由(you)于在(zai)拉(la)伸過程中(zhong)試(shi)(shi)(shi)樣(yang)的(de)(de)變形(xing)，使(shi)得(de)拉(la)伸的(de)(de)施力線(xian)(xian)與試(shi)(shi)(shi)樣(yang)的(de)(de)軸線(xian)(xian)不重合(he)，偏(pian)差更為(wei)顯(xian)著。造成試(shi)(shi)(shi)驗時產(chan)生偏(pian)心(xin)力，除(chu)了電(dian)子拉(la)力試(shi)(shi)(shi)驗機(ji)的(de)(de)構造不良，還(huan)有(you)可能試(shi)(shi)(shi)樣(yang)本身形(xing)狀不對稱、夾頭構造和安裝不正(zheng)確等因素。因此，在(zai)夾具(ju)夾持試(shi)(shi)(shi)樣(yang)時，要使(shi)試(shi)(shi)(shi)樣(yang)縱軸與上(shang)下夾具(ju)中(zhong)心(xin)線(xian)(xian)重合(he)，且松緊適宜，以防(fang)比試(shi)(shi)(shi)樣(yang)滑(hua)脫(tuo)或(huo)斷在(zai)夾具(ju)內(nei)。

1.4試驗(yan)環境

    影響(xiang)塑料拉伸試驗結果的環(huan)境因素主要是溫度(du)和濕(shi)(shi)度(du)。GB/T1040.2-2006規定:標準實驗室環(huan)境溫度(du)為(23±2 )℃，相對(dui)濕(shi)(shi)度(du)為45%～55%。

    熱塑性(xing)塑料的(de)拉(la)伸(shen)性(xing)能測試受溫(wen)(wen)度(du)的(de)影響較大。伴隨著(zhu)溫(wen)(wen)度(du)上升，塑料將(jiang)由硬脆型向黏強(qiang)(qiang)(qiang)型轉(zhuan)變，拉(la)伸(shen)強(qiang)(qiang)(qiang)度(du)和拉(la)伸(shen)彈性(xing)模(mo)量變小，而(er)斷(duan)(duan)裂伸(shen)長(chang)率將(jiang)變大。圖2反映了聚氯(lv)乙烯(PUC)的(de)拉(la)伸(shen)強(qiang)(qiang)(qiang)度(du)、斷(duan)(duan)裂伸(shen)長(chang)率與溫(wen)(wen)度(du)的(de)關系