Engineering: Lab report
Whatever branch of engineering you are studying, many of your labs and lab based assignments will require a written report. The purpose is to report what you did and what you learned from an experiment.
Lab reports can vary in length and format. These range from a form to fill in and submit before leaving the lab, to a formal written report. However, they all usually follow a similar basic structure.
Example: Typical Lab report structure
MEASUREMENT OF THE FRACTURE TOUGHNESS OF PERSPEX
Perspex samples with sharp and blunt cracks were subjected to loads to determine fracture toughness. Results clearly show a correlation between...
To determine the fracture toughness of Perspex.
Fracture toughness is a measure of the fracture resistance of a cracked material. The two types of crack investigated here are shown in Figure 1. For a sharp crack to propagate...
Six Perspex samples with artificial blunt cracks of various sizes were supplied. The samples were secured into the micro-tester and the strain rate and maximum load parameters set to...
Results and Discussion
The six specimens were tested to three loads and the corresponding deflection calculated. The average compliance at each crack length was calculated; these are plotted in Graph 1. The calculated exponent is close to the quadratic relationship...
The experimental results show that fracture toughness decreases with increased crack length and velocity...
Structure of a lab report
A lab report in engineering generally contains the following sections:
The title precisely describes the purpose of the practical work.
The majority of your practical work will involve measurements, observations or the creation of some object of interest.
Chromatographic separation of protein molecules.
It is clear from the title of this lab report that it describes a procedure called a ‘chromatographic separation’ and the objects of interest are ‘protein molecules’.
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The abstract provides a brief overview of the practical work, including key results and conclusions.
Keep your abstract short, about one paragraph or 250 to 500 words. It must be clear enough that the reader can understand the key points of the report without needing to read the rest of it. In general the abstract should answer six questions. Addressing each question should only require one to two sentences:
- Why was the experiment conducted? (Big-picture/real-world view.)
- What specific problem/research question was being addressed?
- What methods were used to solve the problem/answer the question?
- What results were obtained?
- What do these results mean?
- How do the results answer the overall question or improve our understanding of the problem?
Note that there is no need to include background information such as motivation or theory. Shorter lab reports may not require an abstract so check you report guidelines first.
The example abstract below clearly states what the student did, how the student did it, what they found and what it means in relation to their aim. Notice how brief each of these points is.
In this experiment a wind tunnel was used to measure the lift and drag forces on a 1:70 scale model of an aeroplane in order to determine the optimal angle of attack. Angles of attack ranging from -8° to 20° were tested at a wind speed of approximately 30m/s. The typical pressure distribution around an aerofoil at small angles of attack was found to be low on the upper surface and high on the lower surface, creating an upward lift force. As the angle of attack increased, so too did the lift force exerted on the plane from the aerofoil wings. However, there is an optimal angle of attack after which the lift will begin to decrease. This is because increasing the angle of attack also increases the drag on the aerofoil. An 8° angle of attack was found to be optimal.
In any experiment, you aim to do something. For example, to verify, to investigate, to measure, to compare or to test a hypothesis.
- Each aim should have a specific goal. Think about how you will know when you have achieved your aim. This should be apparent from your aim statement.
- Write your aim using verbs (e.g. 'to investigate').
- Where there is a goal-and-means relationship, make sure this is clear. (E.g. to investigate molecular forces via atomic force microscopy.)
- Each aim in your experiment should be written in a complete sentence.
- In the aim statement below, it is clear that the aim will be achieved when a value is obtained for the resistivity of iron.
The aim of the experiment is to determine the resistivity of iron by measuring the resistance of a specimen of wire.
If an experiment has more than one aim, list them in the logical order and make sure the relationship between the aims is made clear The example below has two aims:
1. To measure the pressure distribution around a cylinder in a wind tunnel
2. To calculate the forces on the cylinder based on the data obtained
Note the use of ‘and use the results’ in the example provided.
Example: Two aims
The aim of this experiment is to conduct lift and drag measurements on a scale model aeroplane and use the results to assess the behaviour of a full-scale aeroplane under three hypothetical conditions.
Check your understanding of how to write an effective aim View
Compare the following two aims, and then answer the question below.
AIM A To conduct lift and drag measurements on a model aeroplane in a wind tunnel.
AIM B To measure the lift and drag forces on a model aeroplane in a wind tunnel.
The introduction or background section is where you introduce the topic and purpose of your practical work and narrow down to your hypothesis, aims or the research question you intend to address.To write an introduction section you need to succinctly explain relevant theory and discuss any relevant laws, equations or theorems. This is also where you should indicate the method/s you will use for analysis, such as nodal analysis, numerical modelling or microscopy. In longer reports you may need to support your choice of method with academic literature. You can include any figures, tables or equations necessary to explain the relevant theory. It should also set out any assumptions, and indicate how the data will be processed.
Below is an example of an introduction defining the formula and associated terms for the calculation of thermal efficiency.
Example: Calculations defined in an introduction
Solar lamps will be used to model the incident radiation received by solar heaters from the sun. However, it is not possible to reproduce the uniform radiation flux at the surface of a real collector. Therefore the average radiation flux at the surface of the collector will be used in calculations.
The method section is where you describe what you actually did during the practical work. You need to describe the actions you took during your practical work in a way that someone from your field has enough information to replicate the process and achieve a similar result.
You must also include any unplanned changes to the original process which occurred during the execution of the experiment. A great way to keep track of this is to use a lab notebook during the practical work to note any changes you make.
Turn lab instructions into a lab report method
A common mistake students make is copying the instructions their teachers provide directly into their method section. You will generally be provided with a set of instructions to complete your practical work. These instructions are NOT written in the style of a laboratory report. A typical set of instructions usually includes:
- How apparatus and equipment were set up (e.g. experimental set-up), usually including a diagram,
- A list of materials used,
- Steps used to collect the data,
- Any experimental difficulties encountered and how they were resolved or worked around.
Below is an example of instructions provided to a student to carry out a first year chemical engineering experiment.
Example: Lab instructions
Phrases are used here to specifically instruct the student who may be performing the technique for the first time. For example:
- “Wait until the flow rate has stabilised before proceeding.”
Also note that language used is in the present tense in bullet points. The method section should be written in the past tense as a cohesive paragraph.
Below is an example of how these lab instructions can be successfully paraphrased into a method in a laboratory report.
The flow rate of the feed pump was set to 230mL/min and cooling water was added to the condenser at maximum flow rate. Once the steam had overflowed into the reactor, the pressure was increased to….
Writing about materials and/or experimental setup
- Describe the materials used and/or the apparatus setup.
- Include an image showing the relevant features of any object or material under investigation
- Include a diagram of the experimental setup, with each component clearly labelled
In the example below, the experiment required a particular apparatus setup. Notice how there is a small amount of text describing the setup and two well labelled figures illustrating the apparatus setup.
Example: Experimental setup
The performance of a flat plate solar collector was analysed using a small scale test rig. The rig was as shown in Figure 3, with the exception of the water pipes (see Figure 4). Thermocouples were connected to the collector as shown in Figure 3, and attached at the inlet and outlet of the water pipes to measure ambient temperature.
Figure 3. Flat plate solar collector setup
Figure 4. Wired joint
In the method section you should use the past tense when you are reporting on something you did.
While most engineering units require that you report in the passive voice, some require the active voice. In the example below, the first person is used e.g. "we initiated". This is accepted in some disciplines, but not others. Check your unit information or talk to your teacher.
Evaluate student lab reports View
Read the lab instructions and student reports below, then answer the questions that follow:
The effects of surface roughness on drag force
Cylinder - 2408mm high, 80mm diameter
Wind tunnel working area: 304.8mm x 304.8mm x 812.8mm
- Choose a way to apply temporary rough surfaces to the cylinder. Your chosen method must be able to simulate at least two noticeable variations in surface roughness.
- Calibrate the strain gauge and record a zero reading. You can find the calibration coefficient by applying known masses to the model. The results can then be plotted to determine the calibration factor.
Group A Method
After a long discussion our group chose sandpaper to simulate variations in surface roughness as there is a big difference between the lightest and heaviest grades. To make sure the sandpaper wouldn't come off under high wind velocities, we came up with the idea of sticking it to the cylinder with double-sided tape. We found the calibration coefficient by applying 4 known masses to the model and plotting the results.
Group B Method
It was decided that sandpaper would be the most effective way to simulate variations in surface roughness due to the significant variation between the lightest and heaviest grades. Because the sandpaper will be subjected to very high wind velocities, in order to make sure that it will not be dislodged in the wind tunnel, it will be wrapped around the cylinder and secured with double-sided tape. Before beginning, the strain gauge must be calibrated to obtain a zero reading. The calibration coefficient is found by applying four known masses to the model and plotting the results.
Answer the three questions about the reports below. Scroll down and use the blue dots or arrows to move to the next question.
The results section is where you present a summary of the data collected during your experiments. These results are not just a copy of the raw data from your lab notebook. Rather, it may involve calculation, analysis and the drawing up of tables and figures to present your data.
When you take your raw data and perform some sort of mathematical operation to change it, it is good practice to show the equations you used in your analysis as well as one worked example using each equation. Very long calculations or calculations that you repeat multiple times are usually included in an appendix (see below).
In some disciplines, if formulae are used, it is common to number them as equations:
Error analysis is a type of calculation that indicates the accuracy of your results, usually done through determining the level of uncertainty. The sources of error that you need to consider will vary between experiments and disciplines, but you will usually need to factor in both random and systematic errors.
Any analysis and calculations of the errors or uncertainties in the experiment are included in the results section unless otherwise specified. In some disciplines the analysis and uncertainty calculations are presented under its own heading. Check the requirements given in your unit information or lab manual, or ask your tutor if you are unsure where to place calculations.
Tables and figures
Most numerical data are presented using tables or figures. These need to be clearly labelled following the standard conventions for captions, and titles must tell the reader precisely what data is being presented.
If a measurement is stated in the title, in a column of a table or on the axis of a graph and it has units associated with it, these must be included (usually in brackets).
The table below presents a series of measurements collected during an experiment. Notice the units in every column with the brackets. Some measurements such as pH or Cp do not have units.
The figure below is a graphical representation of aerodynamic measurements. Notice the axes are labelled with appropriate units and the caption at the bottom of the figure clearly describes what the figure is about.
Figures can also be a wide variety of images. The figure below is an image taken from a type of molecular microscope. Notice the caption at the bottom of the figure clearly describing the figure and the specification of the magnification of the microscope.
If you must use figures from another source, indicate in the citation whether you have modified it in any way to avoid collusion or plagiarism.
You must refer to every figure and table in your text, so that the reader understands the content and purpose of each. Explain clearly how you obtained final values, and tell the reader where to find raw data and sample calculations.
To calculate the fracture toughness of Perspex the derivative of 2λ with respect to a is required. Linearizing Graph 1 allows an expression between compliance and crack length to be modelled. The linearized relation form of the relationship allows the power law relationship to be determined as shown below.
The discussion section is where you interpret and evaluate your results. To do this you need to summarise your key results, summarise unexpected results, and explain how your results relate to your aims, hypotheses or literature as stated at the start of the report. Here are some tips on writing discussion sections:
- Summarise key results
- Identify and describe any trends or patterns you have observed. If these are numerical trends simply saying phrases such as ‘higher, lower, increase or decreased’ is vague. Instead give a numeric value in addition to describing an increase or decrease. For example, “an average increase of 510 mL/min”.
- Compare the experimental results with any predictions you made.
- Interpret what the results mean in relation to the aims, research question(s) or hypothesis.
- Summarise key unexpected results
- Describe any results which were unexpected or didn’t match any predictions.
- Suggest explanations for unexpected results based on the theory and procedures within the experiment.
- Evaluate how any sources of error might impact on the interpretation of your results in relation to the aims, research question(s) or hypothesis.
- Discuss limitations
- Clarify how the limitations of the study might affect the accuracy and precision of the answers to your aim, research question or hypothesis.
- Suggest how the experiment or analysis could have been improved.
- Explain how your results do or do not address your aim, research question or hypothesis, and indicate future directions in research.
When discussing your results, begin by directing the reader to the relevant table or graph.
Below are several examples of sentences that are appropriate for a discussion section. Examples 1 and 2 show you sentences which can be used to compare your data to the literature and then explain unusual data. Example 3 shows you how to use these sentences to draw your reader's attention to your results and provide a recommendation.
Example 1: Discussion - Comparing experimental data with data in the literature
Varying the angle of attack in the positive direction increased the lift until the wind reached an angle of attack of 10°, after which it decreased. This is consistent with the standard trend .
Example 2: Discussion - Comparing and contrasting experimental data and explain unusual results
The values found for the pressure coefficients around the cylinder (graph 5) are consistent with the accepted trend for laminar flow (graph 6). The sudden increase in the pressure coefficient at 190° is due to the cylinder becoming dislodged from its position perpendicular to the flow.
Example 3: Discussion - The main features of a discussion
The example below, from an experiment measuring the saturation pressure of water, shows the main features of a Discussion.
Check you understanding; Identify features of a discussion View
The paragraph below contains some, but not all, of the functions of a Discussion. Read the paragraph then answer the five questions that follow. For each sentence, you need to select the appropriate function or functions it is performing.
Figure 5 shows the standard efficiency curve for each of the two collector types investigated. While the data points for the formed fully soldered joint are significantly spread out from the line of best fit, the soldered joint data points lie close to the best-fit line. The latter indicates a strong similarity to standard efficiency curves given in Hessami (2006). Both best-fit lines indicate that efficiency increases with reduction in water mass flow rate, which is characteristic of standard efficiency curves.
The efficiency of the solar collectors could be improved by the use of one-way glass to reduce incident radiation losses due to reflection, as well as by better insulation of the experimental apparatus.
The conclusion section is where you summarise your report. A conclusion is usually one paragraph or 200 to 300 words. In this way a conclusion is very similar to an abstract but with more emphasis on the results and discussion.
Students often make the mistake of thinking a conclusion section is identical to a discussion section. Your conclusion should answer the question: So what? Focus on the significance and relevance of your results in relation to the aim of your experiment.
A conclusion never introduces any new ideas or results. Rather, it provides a concise summary of those which have already been presented in the report. When writing a conclusion you should:
- Briefly restate the purpose of the experiment (the question it was seeking to answer).
- Indicate to what extent the aims of the experiment were achieved.
- Summarise the main points of your findings including key values.
- Summarise important limitations and the cause of unexpected results.
- Recommend improvements to overcome experimental limitations.
Experimental results showed a clear correlation between the collector efficiency of a solar water heater and water mass flow rate. The most efficient of the two collector designs tested was the formed fully soldered joint, due to the greater contact area between collector and pipe maximising heat transfer to the fluid. The optimal efficiency point obtained for this design was at the highest water mass flow tested, 0.095kg/s, suggesting that the actual optimum may be higher. It is therefore recommended that a higher range of flow rates be tested. The data also suggests that an efficiency of over 80% is achievable, and significantly greater than the currently accepted maximum.
When in-text citations are incorporated into your lab report (typically in the introduction or discussion) you must always have the full citations included in a separate reference list. The reference list is a separate section that comes after your conclusion (and before any appendices).
Check your lab manual or unit information to determine which referencing style is preferred. Carefully follow that referencing style for your in-text references and reference list. You can find examples and information about common referencing styles in the Citing and referencing Library guide.
An appendix (plural = appendices) contains material that is too detailed to include in the main report, such as tables of raw data or detailed calculations.
Each appendix must be:
- given a number (or letter) and title
- referred to by number (or letter) at the relevant point in the text.
Example: Referring to an appendix
The calculated values are shown in Table 3 below. For detailed calculations, see Appendix 1.
Check your understanding of the sections of a lab report View
The typical structure of a lab report is shown in the left-hand column below. Can you match the sections with their description? Drag and drop the descriptions from the right-hand column to the section it matches.