舉例說明：寫出專業和優秀的SCI論文引言

02-08

上一篇介紹了「如何寫出優秀和專業的SCI論文的引言」，偏向於理論分享，筆者覺得意猶未盡。為了讓大家更加直觀地了解引言寫作的邏輯結構，筆者選取了一篇自己的SCI論文進行實例分析，為了保證論文的高水平，筆者選擇的是自己研究領域內的頂級期刊（IF=4.762）－Cement and Concrete Research。見下圖。

研究的問題/領域是什麼？（研究範圍）

引言第一段：Most concrete structures in service are inevitably subjected to some amount of drying-induced shrinkage. If shrinkage is restrained, whether externally or internally, tensile stresses will develop and potentially cause cracking of the concrete. Externally restrained shrinkage can produce large cracks visible to the unaided eye, while internally restrained shrinkage tends to produce fine microcracks near the exposed surfaces. Drying-induced microcracks have widths much smaller than 100 μm and occur when shrinkage is internally restrained by the underlying material due to non-uniform drying across a thick sample, and/or by the presence of stiff aggregate particles. The main parameters influencing the microcracks formed are the rate of drying, thickness of the sample, size and volume fraction of aggregate particles, the aggregate–paste bond, the tensile strength and creep properties of the cement paste matrix, and stiffness contrast between aggregate and paste [1–4].

引言第一段介紹混凝土結構在環境中受到乾燥而收縮，從而引起微觀裂縫，簡單介紹影響它形成的因素。因此論文圍繞著是微觀裂縫而展開研究。

為什麼重要？

引言第二段：It has long been suspected that microcracks could facilitate the transport of aggressive agents and that this would impact on the durability of concrete structures. However, the literature contains very few studies that have directly characterised the microcracks and correlated their characteristics to mass transport properties of concrete. The lack of work concerning the influence of drying-induced microcracks on transport properties is partly due to experimental difficulties in making direct measurements of cracks that are very small, scattered and nonuniformly distributed in the microstructure. It is also very difficult to isolate the influence of microcracks from other factors such as moisture content and accessible porosity that inevitably change when concrete is dried, but have major influences on transport. Sample preparation may also induce artefacts. This is in contrast to the numerous studies that have been carried out on the transport properties of cementitious materials with mechanically-induced damage, for example Refs. [5–14], where cracks are larger and often propagate through the sample, and their size and location can be relatively well-controlled in the laboratory.

引言第二段馬上指出微觀裂縫對混凝土的耐久性（混凝土材料抵抗外界因素長期破壞作用的能力）有影響，而且很少有相關的研究，以此凸顯出本論文研究的重要性。

目前的主要研究或發現的成果？

引言第三段：Studies using microscopy techniques have observed that neat cement pastes when subjected to drying form a cell-like crack pattern (map-cracking) on the surface, and that the microcracks form perpendicular to the dried surface, but with limited penetration depth [3,15,16]. In cement-based composites containing aggregate, drying shrinkage induces radial (matrix) and circumferential (bond) microcracks around aggregate particles [17–19]. To facilitate understanding of the underlying mechanisms causing microcracking, a number of experimental and numerical studies have been carried out on model systems. These are essentially two-dimensional or very thin cementitious composites containing mono-sized aggregate inclusions (glass spheres, steel rods) at relatively low volume fractions [18,20–23]. These studies collectively show that radial cracks typically occur along the shortest distance connecting neighbouring aggregates,and that increasing aggregate size at constant volume fraction increases the degree of microcracking. Some studies have also suggested that a critical aggregate size exists,below which drying shrinkage produces an insignificant amount of microcracking [18,23].

引言第三段概括目前相關的研究成果。

尚未解決的問題？或已有問題沒有被科學解釋清楚？

引言第四段：To what extent studies on model systems relate to real mortars and concretes is unclear. Cement-based composites can be free of cracks provided that the drying rate is extremely low or the sample thickness is limited to a few millimetres [2], but these conditions are rarely met, so it is reasonable to assume that most concrete structures are microcracked. The question that is of most practical significance is to what degree the microcracks influence transport properties and long-term durability. A related issue that lacks understanding is the influence of size effects (sample thickness and aggregate size) on microcracking and measured transport properties. Conventional laboratory transport tests typically involve applying a pressure, concentration or potential gradient, and measuring the flux through the sample. Obviously, the volume of tested material should be large enough to be representative. Sample thickness (t) in the direction of flow should also be several times the maximum aggregate size (MSA) to prevent flux being dominated by short circuits through cracks or the porous interface of a single large aggregate. Table 1 summarises the recommended drying regimes and sample dimensions in several standardised transport test methods. A t/MSA ratio of ≥3 is specified in several tests, but it is not well established that this is sufficient to provide representative measurements.

引言第四段指出目前研究存在的問題：微觀裂縫對耐久性影響多大不清楚，且目前測量的樣本和骨料大小不統一，導致的測量結果不一定具有代表性。

引言第五段：The published literature contains a vast number of papers on the mass transport properties of cement-based materials. However, studies where aggregate size is a variable are limited and do not provide a clear and consistent answer as to whether a significant aggregate and sample size effect on transport exists. Data from some suggest that increasing aggregate size increases measured transport [37–40], while others show insignificant influence [41,42] or even opposing trends [43]. Most studies looked at a small range of aggregate sizes, at constant sample thickness, and very few have considered the possible influence of microcracks or related their observations to the t/MSA ratio [19,40,44]. The inconsistent findings may also be due to several influencing parameters that vary (but may not be considered) in experiments, which underscore the difficulty of isolating the effect of microcracks.

緊接著第四段，引言第五段再進一步通過已有的文獻支撐說明目前研究方法存在的問題。

你的研究目標和方法？（將提供什麼新方法/數據/模型/理論去解決問題？)

引言第六段：Theaim of this paper is to study the effect of sample thickness, aggregate size and the t/MSA ratio on drying-induced microcracking and to understand its influence on transport properties. Mortars and concretes with t/MSA ratio ranging from 2.5 to 20 were prepared by varying the sample thickness or aggregate size distribution, and then dried in several ways to induce microcracks. Gas diffusion, gas permeation and capillary absorption were tested because the influence of microcracks may be dependent on the transport mechanism. All samples had the same free w/c ratio, aggregate volume fraction and curing age to ensure consistent porosity at the time of testing. Microcracks were characterised using image analysis and correlated to transport results. The study is focussed on establishing if there is an aggregate and sample size effect on transport, and whether a critical t/MSA ratio exists, beyond which the size effect or the influence of microcracks becomes negligible. The understanding gained will help in interpretation of mass transport measurements, which are increasingly used as performance indicators. It will also facilitate modelling of transport properties from microstructure (e.g. should microcracks be included?). A more practical motivation for this study is to help understand the influence of drying-induced microcracks on durability of most real concrete structures.

引言第六段明確提出論文研究的目標以及具體的執行方法，也提了該研究對實際工程帶來的意義。

從上面分解可以看出，引言的寫作是有章可循，按照筆者建議的思維結構的五個方面依次寫作即可。當然針對每個具體研究方向，會有所差別，需要自己把握。此外，筆者希望傳達一種思維：SCI論文的確是有規律可循，但是想要做到透徹分析還需要紮實的研究基本功和優秀的研究內容。

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