Adhesion and strength of viscoelastic solids. Is there a relationship between adhesion and bulk properties?
Adhesion and strength of viscoelastic solids. Is there a relationship between adhesion and bulk properties?
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DOI：
10.1021/la950887q
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发表时间：
1996-09-18
期刊：
影响因子：
3.9
通讯作者：
Gent, AN
中科院分区：
文献类型：
--
作者：
Gent, AN
粘合强度取决于粘合剂的流变性及其与基材的相互作用。这一点通过使用两块橡胶板之间不同数量的相互连接制备的模型接头的研究表明。每单位界面面积的断裂能G似乎是两项的乘积：G=G（0）[1+f（R，T）]，其中G（0）是界面的固有（化学）强度，f（R，T）通常比1大得多，反映了在裂纹速度R和温度T下粘附体内粘弹性耗散的能量。G（0）值的范围从非粘合片材的几乎为零到橡胶的阈值撕裂强度50-80 J/m（2），与界面粘合的密度成比例。G值在高速和低温下大1000倍。软橡胶状固体的撕裂强度也因内能损失而增加，并显示出对撕裂速率的同样显著的依赖性。通过比较撕裂强度增加某一因子的速率R与弹性模量μ增加相同因子的角频率ω，可以估计裂纹尖端耗散区的长度δ：δ =R/ω。但是，以这种方式获得的值仅为约1埃，太小而不能代表橡胶中的实际耗散区。相反，断裂似乎是间歇性地发生的，裂纹以高速增长，然后停止。裂纹止裂的一种可能机制是裂纹尖端的劈裂。事实上，通过比较撕裂强度和切割阻力可以推断出尖端钝化，当钝化受到抑制时，切割阻力随着状态的增加和温度的降低而缓慢得多。因此，许多观察到的撕裂强度的软粘合剂和软固体是由于裂纹尖端钝化，需要进一步的研究，以建立钝化过程的确切性质，以及它是如何相关的（因为它显然是）粘弹性和耗散性能。提请注意在粘附科学的其他悬而未决的问题。
Strength of adhesion depends upon the rheology of an adhesive as well as upon its interaction with a substrate, This is shown by studies using model joints prepared with different amounts ofinterlinking between two rubber sheets. The fracture energy G per unit of interfacial area appears to be a product of two terms: G=G(0)[1+f(R,T)] where G(0) is the intrinsic (chemical) strength of the interface and f(R,T), usually much larger than unity, reflects energy dissipated viscoelastically within the adherends at a crack speed R and temperature T. Values of G(0) range from virtually zero for nonbonded sheets up to the threshold tear strength of rubber, 50-80 J/m(2), in proportion to the density of interfacial bonds, Values of G are as much as 1000 x greater at high speeds and low temperatures, Like adhesion, the tear strength of a soft rubbery solid is also increased by internal energy losses and shows the same marked dependence upon rate of tearing. By comparing the rate R at which tear strength increases by a certain factor with the angular frequency omega at which the elastic modulus mu increases by the same factor the length delta of the dissipative zone at the crack tip can be estimated: delta=R/omega. But values obtained in this way are only about 1 Angstrom, too small to represent an actual dissipation zone in rubber. It seems likely instead that fracture takes place intermittently, the crack growing at high speed and then stopping. A possible mechanism of crack stopping is by splitting at the crack tip. Indeed, tip blunting can be inferred by comparing tear strength with resistance to cutting, when blunting is suppressed, Cutting resistance increases much more slowly with increasing sate and decreasing temperature. Thus, much of the observed tear strength of soft adhesives and soft solids is attributed to crack-tip blunting, Further research is needed to establish the exact nature of the blunting process and how it is related (as it clearly is) to viscoelastic and dissipative properties. Attention is drawn to other unresolved issues in adhesion science.